text: // PouchDB 6.0.5
  // 
  // (c) 2012-2016 Dale Harvey and the PouchDB team
  // PouchDB may be freely distributed under the Apache license, version 2.0.
  // For all details and documentation:
  // http://pouchdb.com
  (function(f){if(typeof exports==="object"&&typeof module!=="undefined"){module.exports=f()}else if(typeof define==="function"&&define.amd){define([],f)}else{var g;if(typeof window!=="undefined"){g=window}else if(typeof global!=="undefined"){g=global}else if(typeof self!=="undefined"){g=self}else{g=this}g.PouchDB = f()}})(function(){var define,module,exports;return (function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw f.code="MODULE_NOT_FOUND",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(_dereq_,module,exports){
  'use strict';
  
  module.exports = argsArray;
  
  function argsArray(fun) {
    return function () {
      var len = arguments.length;
      if (len) {
        var args = [];
        var i = -1;
        while (++i < len) {
          args[i] = arguments[i];
        }
        return fun.call(this, args);
      } else {
        return fun.call(this, []);
      }
    };
  }
  },{}],2:[function(_dereq_,module,exports){
  
  /**
   * This is the web browser implementation of `debug()`.
   *
   * Expose `debug()` as the module.
   */
  
  exports = module.exports = _dereq_(3);
  exports.log = log;
  exports.formatArgs = formatArgs;
  exports.save = save;
  exports.load = load;
  exports.useColors = useColors;
  exports.storage = 'undefined' != typeof chrome
                 && 'undefined' != typeof chrome.storage
                    ? chrome.storage.local
                    : localstorage();
  
  /**
   * Colors.
   */
  
  exports.colors = [
    'lightseagreen',
    'forestgreen',
    'goldenrod',
    'dodgerblue',
    'darkorchid',
    'crimson'
  ];
  
  /**
   * Currently only WebKit-based Web Inspectors, Firefox >= v31,
   * and the Firebug extension (any Firefox version) are known
   * to support "%c" CSS customizations.
   *
   * TODO: add a `localStorage` variable to explicitly enable/disable colors
   */
  
  function useColors() {
    // is webkit? http://stackoverflow.com/a/16459606/376773
    return ('WebkitAppearance' in document.documentElement.style) ||
      // is firebug? http://stackoverflow.com/a/398120/376773
      (window.console && (console.firebug || (console.exception && console.table))) ||
      // is firefox >= v31?
      // https://developer.mozilla.org/en-US/docs/Tools/Web_Console#Styling_messages
      (navigator.userAgent.toLowerCase().match(/firefox\/(\d+)/) && parseInt(RegExp.$1, 10) >= 31);
  }
  
  /**
   * Map %j to `JSON.stringify()`, since no Web Inspectors do that by default.
   */
  
  exports.formatters.j = function(v) {
    return JSON.stringify(v);
  };
  
  
  /**
   * Colorize log arguments if enabled.
   *
   * @api public
   */
  
  function formatArgs() {
    var args = arguments;
    var useColors = this.useColors;
  
    args[0] = (useColors ? '%c' : '')
      + this.namespace
      + (useColors ? ' %c' : ' ')
      + args[0]
      + (useColors ? '%c ' : ' ')
      + '+' + exports.humanize(this.diff);
  
    if (!useColors) return args;
  
    var c = 'color: ' + this.color;
    args = [args[0], c, 'color: inherit'].concat(Array.prototype.slice.call(args, 1));
  
    // the final "%c" is somewhat tricky, because there could be other
    // arguments passed either before or after the %c, so we need to
    // figure out the correct index to insert the CSS into
    var index = 0;
    var lastC = 0;
    args[0].replace(/%[a-z%]/g, function(match) {
      if ('%%' === match) return;
      index++;
      if ('%c' === match) {
        // we only are interested in the *last* %c
        // (the user may have provided their own)
        lastC = index;
      }
    });
  
    args.splice(lastC, 0, c);
    return args;
  }
  
  /**
   * Invokes `console.log()` when available.
   * No-op when `console.log` is not a "function".
   *
   * @api public
   */
  
  function log() {
    // this hackery is required for IE8/9, where
    // the `console.log` function doesn't have 'apply'
    return 'object' === typeof console
      && console.log
      && Function.prototype.apply.call(console.log, console, arguments);
  }
  
  /**
   * Save `namespaces`.
   *
   * @param {String} namespaces
   * @api private
   */
  
  function save(namespaces) {
    try {
      if (null == namespaces) {
        exports.storage.removeItem('debug');
      } else {
        exports.storage.debug = namespaces;
      }
    } catch(e) {}
  }
  
  /**
   * Load `namespaces`.
   *
   * @return {String} returns the previously persisted debug modes
   * @api private
   */
  
  function load() {
    var r;
    try {
      r = exports.storage.debug;
    } catch(e) {}
    return r;
  }
  
  /**
   * Enable namespaces listed in `localStorage.debug` initially.
   */
  
  exports.enable(load());
  
  /**
   * Localstorage attempts to return the localstorage.
   *
   * This is necessary because safari throws
   * when a user disables cookies/localstorage
   * and you attempt to access it.
   *
   * @return {LocalStorage}
   * @api private
   */
  
  function localstorage(){
    try {
      return window.localStorage;
    } catch (e) {}
  }
  
  },{"3":3}],3:[function(_dereq_,module,exports){
  
  /**
   * This is the common logic for both the Node.js and web browser
   * implementations of `debug()`.
   *
   * Expose `debug()` as the module.
   */
  
  exports = module.exports = debug;
  exports.coerce = coerce;
  exports.disable = disable;
  exports.enable = enable;
  exports.enabled = enabled;
  exports.humanize = _dereq_(10);
  
  /**
   * The currently active debug mode names, and names to skip.
   */
  
  exports.names = [];
  exports.skips = [];
  
  /**
   * Map of special "%n" handling functions, for the debug "format" argument.
   *
   * Valid key names are a single, lowercased letter, i.e. "n".
   */
  
  exports.formatters = {};
  
  /**
   * Previously assigned color.
   */
  
  var prevColor = 0;
  
  /**
   * Previous log timestamp.
   */
  
  var prevTime;
  
  /**
   * Select a color.
   *
   * @return {Number}
   * @api private
   */
  
  function selectColor() {
    return exports.colors[prevColor++ % exports.colors.length];
  }
  
  /**
   * Create a debugger with the given `namespace`.
   *
   * @param {String} namespace
   * @return {Function}
   * @api public
   */
  
  function debug(namespace) {
  
    // define the `disabled` version
    function disabled() {
    }
    disabled.enabled = false;
  
    // define the `enabled` version
    function enabled() {
  
      var self = enabled;
  
      // set `diff` timestamp
      var curr = +new Date();
      var ms = curr - (prevTime || curr);
      self.diff = ms;
      self.prev = prevTime;
      self.curr = curr;
      prevTime = curr;
  
      // add the `color` if not set
      if (null == self.useColors) self.useColors = exports.useColors();
      if (null == self.color && self.useColors) self.color = selectColor();
  
      var args = Array.prototype.slice.call(arguments);
  
      args[0] = exports.coerce(args[0]);
  
      if ('string' !== typeof args[0]) {
        // anything else let's inspect with %o
        args = ['%o'].concat(args);
      }
  
      // apply any `formatters` transformations
      var index = 0;
      args[0] = args[0].replace(/%([a-z%])/g, function(match, format) {
        // if we encounter an escaped % then don't increase the array index
        if (match === '%%') return match;
        index++;
        var formatter = exports.formatters[format];
        if ('function' === typeof formatter) {
          var val = args[index];
          match = formatter.call(self, val);
  
          // now we need to remove `args[index]` since it's inlined in the `format`
          args.splice(index, 1);
          index--;
        }
        return match;
      });
  
      if ('function' === typeof exports.formatArgs) {
        args = exports.formatArgs.apply(self, args);
      }
      var logFn = enabled.log || exports.log || console.log.bind(console);
      logFn.apply(self, args);
    }
    enabled.enabled = true;
  
    var fn = exports.enabled(namespace) ? enabled : disabled;
  
    fn.namespace = namespace;
  
    return fn;
  }
  
  /**
   * Enables a debug mode by namespaces. This can include modes
   * separated by a colon and wildcards.
   *
   * @param {String} namespaces
   * @api public
   */
  
  function enable(namespaces) {
    exports.save(namespaces);
  
    var split = (namespaces || '').split(/[\s,]+/);
    var len = split.length;
  
    for (var i = 0; i < len; i++) {
      if (!split[i]) continue; // ignore empty strings
      namespaces = split[i].replace(/\*/g, '.*?');
      if (namespaces[0] === '-') {
        exports.skips.push(new RegExp('^' + namespaces.substr(1) + '$'));
      } else {
        exports.names.push(new RegExp('^' + namespaces + '$'));
      }
    }
  }
  
  /**
   * Disable debug output.
   *
   * @api public
   */
  
  function disable() {
    exports.enable('');
  }
  
  /**
   * Returns true if the given mode name is enabled, false otherwise.
   *
   * @param {String} name
   * @return {Boolean}
   * @api public
   */
  
  function enabled(name) {
    var i, len;
    for (i = 0, len = exports.skips.length; i < len; i++) {
      if (exports.skips[i].test(name)) {
        return false;
      }
    }
    for (i = 0, len = exports.names.length; i < len; i++) {
      if (exports.names[i].test(name)) {
        return true;
      }
    }
    return false;
  }
  
  /**
   * Coerce `val`.
   *
   * @param {Mixed} val
   * @return {Mixed}
   * @api private
   */
  
  function coerce(val) {
    if (val instanceof Error) return val.stack || val.message;
    return val;
  }
  
  },{"10":10}],4:[function(_dereq_,module,exports){
  (function (root, factory) {
    /* istanbul ignore next */
    if (typeof define === 'function' && define.amd) {
      define([], factory)
    } else if (typeof exports === 'object') {
      module.exports = factory()
    } else {
      root.PromisePool = factory()
      // Legacy API
      root.promisePool = root.PromisePool
    }
  })(this, function () {
    'use strict'
  
    var EventTarget = function () {
      this._listeners = {}
    }
  
    EventTarget.prototype.addEventListener = function (type, listener) {
      this._listeners[type] = this._listeners[type] || []
      if (this._listeners[type].indexOf(listener) < 0) {
        this._listeners[type].push(listener)
      }
    }
  
    EventTarget.prototype.removeEventListener = function (type, listener) {
      if (this._listeners[type]) {
        var p = this._listeners[type].indexOf(listener)
        if (p >= 0) {
          this._listeners[type].splice(p, 1)
        }
      }
    }
  
    EventTarget.prototype.dispatchEvent = function (evt) {
      if (this._listeners[evt.type] && this._listeners[evt.type].length) {
        var listeners = this._listeners[evt.type].slice()
        for (var i = 0, l = listeners.length; i < l; ++i) {
          listeners[i].call(this, evt)
        }
      }
    }
  
    var isGenerator = function (func) {
      return (typeof func.constructor === 'function' &&
        func.constructor.name === 'GeneratorFunction')
    }
  
    var functionToIterator = function (func) {
      return {
        next: function () {
          var promise = func()
          return promise ? {value: promise} : {done: true}
        }
      }
    }
  
    var promiseToIterator = function (promise) {
      var called = false
      return {
        next: function () {
          if (called) {
            return {done: true}
          }
          called = true
          return {value: promise}
        }
      }
    }
  
    var toIterator = function (obj, Promise) {
      var type = typeof obj
      if (type === 'object') {
        if (typeof obj.next === 'function') {
          return obj
        }
        /* istanbul ignore else */
        if (typeof obj.then === 'function') {
          return promiseToIterator(obj)
        }
      }
      if (type === 'function') {
        return isGenerator(obj) ? obj() : functionToIterator(obj)
      }
      return promiseToIterator(Promise.resolve(obj))
    }
  
    var PromisePoolEvent = function (target, type, data) {
      this.target = target
      this.type = type
      this.data = data
    }
  
    var PromisePool = function (source, concurrency, options) {
      EventTarget.call(this)
      if (typeof concurrency !== 'number' ||
          Math.floor(concurrency) !== concurrency ||
          concurrency < 1) {
        throw new Error('Invalid concurrency')
      }
      this._concurrency = concurrency
      this._options = options || {}
      this._options.promise = this._options.promise || Promise
      this._iterator = toIterator(source, this._options.promise)
      this._done = false
      this._size = 0
      this._promise = null
      this._callbacks = null
    }
    PromisePool.prototype = new EventTarget()
    PromisePool.prototype.constructor = PromisePool
  
    PromisePool.prototype.concurrency = function (value) {
      if (typeof value !== 'undefined') {
        this._concurrency = value
        if (this.active()) {
          this._proceed()
        }
      }
      return this._concurrency
    }
  
    PromisePool.prototype.size = function () {
      return this._size
    }
  
    PromisePool.prototype.active = function () {
      return !!this._promise
    }
  
    PromisePool.prototype.promise = function () {
      return this._promise
    }
  
    PromisePool.prototype.start = function () {
      var that = this
      var Promise = this._options.promise
      this._promise = new Promise(function (resolve, reject) {
        that._callbacks = {
          reject: reject,
          resolve: resolve
        }
        that._proceed()
      })
      return this._promise
    }
  
    PromisePool.prototype._fireEvent = function (type, data) {
      this.dispatchEvent(new PromisePoolEvent(this, type, data))
    }
  
    PromisePool.prototype._settle = function (error) {
      if (error) {
        this._callbacks.reject(error)
      } else {
        this._callbacks.resolve()
      }
      this._promise = null
      this._callbacks = null
    }
  
    PromisePool.prototype._onPooledPromiseFulfilled = function (promise, result) {
      this._size--
      if (this.active()) {
        this._fireEvent('fulfilled', {
          promise: promise,
          result: result
        })
        this._proceed()
      }
    }
  
    PromisePool.prototype._onPooledPromiseRejected = function (promise, error) {
      this._size--
      if (this.active()) {
        this._fireEvent('rejected', {
          promise: promise,
          error: error
        })
        this._settle(error || new Error('Unknown error'))
      }
    }
  
    PromisePool.prototype._trackPromise = function (promise) {
      var that = this
      promise
        .then(function (result) {
          that._onPooledPromiseFulfilled(promise, result)
        }, function (error) {
          that._onPooledPromiseRejected(promise, error)
        })['catch'](function (err) {
          that._settle(new Error('Promise processing failed: ' + err))
        })
    }
  
    PromisePool.prototype._proceed = function () {
      if (!this._done) {
        var result = null
        while (this._size < this._concurrency &&
            !(result = this._iterator.next()).done) {
          this._size++
          this._trackPromise(result.value)
        }
        this._done = (result === null || !!result.done)
      }
      if (this._done && this._size === 0) {
        this._settle()
      }
    }
  
    PromisePool.PromisePoolEvent = PromisePoolEvent
    // Legacy API
    PromisePool.PromisePool = PromisePool
  
    return PromisePool
  })
  
  },{}],5:[function(_dereq_,module,exports){
  // Copyright Joyent, Inc. and other Node contributors.
  //
  // Permission is hereby granted, free of charge, to any person obtaining a
  // copy of this software and associated documentation files (the
  // "Software"), to deal in the Software without restriction, including
  // without limitation the rights to use, copy, modify, merge, publish,
  // distribute, sublicense, and/or sell copies of the Software, and to permit
  // persons to whom the Software is furnished to do so, subject to the
  // following conditions:
  //
  // The above copyright notice and this permission notice shall be included
  // in all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  // OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
  // NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
  // DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
  // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
  // USE OR OTHER DEALINGS IN THE SOFTWARE.
  
  function EventEmitter() {
    this._events = this._events || {};
    this._maxListeners = this._maxListeners || undefined;
  }
  module.exports = EventEmitter;
  
  // Backwards-compat with node 0.10.x
  EventEmitter.EventEmitter = EventEmitter;
  
  EventEmitter.prototype._events = undefined;
  EventEmitter.prototype._maxListeners = undefined;
  
  // By default EventEmitters will print a warning if more than 10 listeners are
  // added to it. This is a useful default which helps finding memory leaks.
  EventEmitter.defaultMaxListeners = 10;
  
  // Obviously not all Emitters should be limited to 10. This function allows
  // that to be increased. Set to zero for unlimited.
  EventEmitter.prototype.setMaxListeners = function(n) {
    if (!isNumber(n) || n < 0 || isNaN(n))
      throw TypeError('n must be a positive number');
    this._maxListeners = n;
    return this;
  };
  
  EventEmitter.prototype.emit = function(type) {
    var er, handler, len, args, i, listeners;
  
    if (!this._events)
      this._events = {};
  
    // If there is no 'error' event listener then throw.
    if (type === 'error') {
      if (!this._events.error ||
          (isObject(this._events.error) && !this._events.error.length)) {
        er = arguments[1];
        if (er instanceof Error) {
          throw er; // Unhandled 'error' event
        } else {
          // At least give some kind of context to the user
          var err = new Error('Uncaught, unspecified "error" event. (' + er + ')');
          err.context = er;
          throw err;
        }
      }
    }
  
    handler = this._events[type];
  
    if (isUndefined(handler))
      return false;
  
    if (isFunction(handler)) {
      switch (arguments.length) {
        // fast cases
        case 1:
          handler.call(this);
          break;
        case 2:
          handler.call(this, arguments[1]);
          break;
        case 3:
          handler.call(this, arguments[1], arguments[2]);
          break;
        // slower
        default:
          args = Array.prototype.slice.call(arguments, 1);
          handler.apply(this, args);
      }
    } else if (isObject(handler)) {
      args = Array.prototype.slice.call(arguments, 1);
      listeners = handler.slice();
      len = listeners.length;
      for (i = 0; i < len; i++)
        listeners[i].apply(this, args);
    }
  
    return true;
  };
  
  EventEmitter.prototype.addListener = function(type, listener) {
    var m;
  
    if (!isFunction(listener))
      throw TypeError('listener must be a function');
  
    if (!this._events)
      this._events = {};
  
    // To avoid recursion in the case that type === "newListener"! Before
    // adding it to the listeners, first emit "newListener".
    if (this._events.newListener)
      this.emit('newListener', type,
                isFunction(listener.listener) ?
                listener.listener : listener);
  
    if (!this._events[type])
      // Optimize the case of one listener. Don't need the extra array object.
      this._events[type] = listener;
    else if (isObject(this._events[type]))
      // If we've already got an array, just append.
      this._events[type].push(listener);
    else
      // Adding the second element, need to change to array.
      this._events[type] = [this._events[type], listener];
  
    // Check for listener leak
    if (isObject(this._events[type]) && !this._events[type].warned) {
      if (!isUndefined(this._maxListeners)) {
        m = this._maxListeners;
      } else {
        m = EventEmitter.defaultMaxListeners;
      }
  
      if (m && m > 0 && this._events[type].length > m) {
        this._events[type].warned = true;
        console.error('(node) warning: possible EventEmitter memory ' +
                      'leak detected. %d listeners added. ' +
                      'Use emitter.setMaxListeners() to increase limit.',
                      this._events[type].length);
        if (typeof console.trace === 'function') {
          // not supported in IE 10
          console.trace();
        }
      }
    }
  
    return this;
  };
  
  EventEmitter.prototype.on = EventEmitter.prototype.addListener;
  
  EventEmitter.prototype.once = function(type, listener) {
    if (!isFunction(listener))
      throw TypeError('listener must be a function');
  
    var fired = false;
  
    function g() {
      this.removeListener(type, g);
  
      if (!fired) {
        fired = true;
        listener.apply(this, arguments);
      }
    }
  
    g.listener = listener;
    this.on(type, g);
  
    return this;
  };
  
  // emits a 'removeListener' event iff the listener was removed
  EventEmitter.prototype.removeListener = function(type, listener) {
    var list, position, length, i;
  
    if (!isFunction(listener))
      throw TypeError('listener must be a function');
  
    if (!this._events || !this._events[type])
      return this;
  
    list = this._events[type];
    length = list.length;
    position = -1;
  
    if (list === listener ||
        (isFunction(list.listener) && list.listener === listener)) {
      delete this._events[type];
      if (this._events.removeListener)
        this.emit('removeListener', type, listener);
  
    } else if (isObject(list)) {
      for (i = length; i-- > 0;) {
        if (list[i] === listener ||
            (list[i].listener && list[i].listener === listener)) {
          position = i;
          break;
        }
      }
  
      if (position < 0)
        return this;
  
      if (list.length === 1) {
        list.length = 0;
        delete this._events[type];
      } else {
        list.splice(position, 1);
      }
  
      if (this._events.removeListener)
        this.emit('removeListener', type, listener);
    }
  
    return this;
  };
  
  EventEmitter.prototype.removeAllListeners = function(type) {
    var key, listeners;
  
    if (!this._events)
      return this;
  
    // not listening for removeListener, no need to emit
    if (!this._events.removeListener) {
      if (arguments.length === 0)
        this._events = {};
      else if (this._events[type])
        delete this._events[type];
      return this;
    }
  
    // emit removeListener for all listeners on all events
    if (arguments.length === 0) {
      for (key in this._events) {
        if (key === 'removeListener') continue;
        this.removeAllListeners(key);
      }
      this.removeAllListeners('removeListener');
      this._events = {};
      return this;
    }
  
    listeners = this._events[type];
  
    if (isFunction(listeners)) {
      this.removeListener(type, listeners);
    } else if (listeners) {
      // LIFO order
      while (listeners.length)
        this.removeListener(type, listeners[listeners.length - 1]);
    }
    delete this._events[type];
  
    return this;
  };
  
  EventEmitter.prototype.listeners = function(type) {
    var ret;
    if (!this._events || !this._events[type])
      ret = [];
    else if (isFunction(this._events[type]))
      ret = [this._events[type]];
    else
      ret = this._events[type].slice();
    return ret;
  };
  
  EventEmitter.prototype.listenerCount = function(type) {
    if (this._events) {
      var evlistener = this._events[type];
  
      if (isFunction(evlistener))
        return 1;
      else if (evlistener)
        return evlistener.length;
    }
    return 0;
  };
  
  EventEmitter.listenerCount = function(emitter, type) {
    return emitter.listenerCount(type);
  };
  
  function isFunction(arg) {
    return typeof arg === 'function';
  }
  
  function isNumber(arg) {
    return typeof arg === 'number';
  }
  
  function isObject(arg) {
    return typeof arg === 'object' && arg !== null;
  }
  
  function isUndefined(arg) {
    return arg === void 0;
  }
  
  },{}],6:[function(_dereq_,module,exports){
  (function (global){
  'use strict';
  var Mutation = global.MutationObserver || global.WebKitMutationObserver;
  
  var scheduleDrain;
  
  {
    if (Mutation) {
      var called = 0;
      var observer = new Mutation(nextTick);
      var element = global.document.createTextNode('');
      observer.observe(element, {
        characterData: true
      });
      scheduleDrain = function () {
        element.data = (called = ++called % 2);
      };
    } else if (!global.setImmediate && typeof global.MessageChannel !== 'undefined') {
      var channel = new global.MessageChannel();
      channel.port1.onmessage = nextTick;
      scheduleDrain = function () {
        channel.port2.postMessage(0);
      };
    } else if ('document' in global && 'onreadystatechange' in global.document.createElement('script')) {
      scheduleDrain = function () {
  
        // Create a <script> element; its readystatechange event will be fired asynchronously once it is inserted
        // into the document. Do so, thus queuing up the task. Remember to clean up once it's been called.
        var scriptEl = global.document.createElement('script');
        scriptEl.onreadystatechange = function () {
          nextTick();
  
          scriptEl.onreadystatechange = null;
          scriptEl.parentNode.removeChild(scriptEl);
          scriptEl = null;
        };
        global.document.documentElement.appendChild(scriptEl);
      };
    } else {
      scheduleDrain = function () {
        setTimeout(nextTick, 0);
      };
    }
  }
  
  var draining;
  var queue = [];
  //named nextTick for less confusing stack traces
  function nextTick() {
    draining = true;
    var i, oldQueue;
    var len = queue.length;
    while (len) {
      oldQueue = queue;
      queue = [];
      i = -1;
      while (++i < len) {
        oldQueue[i]();
      }
      len = queue.length;
    }
    draining = false;
  }
  
  module.exports = immediate;
  function immediate(task) {
    if (queue.push(task) === 1 && !draining) {
      scheduleDrain();
    }
  }
  
  }).call(this,typeof global !== "undefined" ? global : typeof self !== "undefined" ? self : typeof window !== "undefined" ? window : {})
  },{}],7:[function(_dereq_,module,exports){
  if (typeof Object.create === 'function') {
    // implementation from standard node.js 'util' module
    module.exports = function inherits(ctor, superCtor) {
      ctor.super_ = superCtor
      ctor.prototype = Object.create(superCtor.prototype, {
        constructor: {
          value: ctor,
          enumerable: false,
          writable: true,
          configurable: true
        }
      });
    };
  } else {
    // old school shim for old browsers
    module.exports = function inherits(ctor, superCtor) {
      ctor.super_ = superCtor
      var TempCtor = function () {}
      TempCtor.prototype = superCtor.prototype
      ctor.prototype = new TempCtor()
      ctor.prototype.constructor = ctor
    }
  }
  
  },{}],8:[function(_dereq_,module,exports){
  (function(factory) {
    if(typeof exports === 'object') {
      factory(exports);
    } else {
      factory(this);
    }
  }).call(this, function(root) { 
  
    var slice   = Array.prototype.slice,
        each    = Array.prototype.forEach;
  
    var extend = function(obj) {
      if(typeof obj !== 'object') throw obj + ' is not an object' ;
  
      var sources = slice.call(arguments, 1); 
  
      each.call(sources, function(source) {
        if(source) {
          for(var prop in source) {
            if(typeof source[prop] === 'object' && obj[prop]) {
              extend.call(obj, obj[prop], source[prop]);
            } else {
              obj[prop] = source[prop];
            }
          } 
        }
      });
  
      return obj;
    }
  
    root.extend = extend;
  });
  
  },{}],9:[function(_dereq_,module,exports){
  'use strict';
  var immediate = _dereq_(6);
  
  /* istanbul ignore next */
  function INTERNAL() {}
  
  var handlers = {};
  
  var REJECTED = ['REJECTED'];
  var FULFILLED = ['FULFILLED'];
  var PENDING = ['PENDING'];
  
  module.exports = Promise;
  
  function Promise(resolver) {
    if (typeof resolver !== 'function') {
      throw new TypeError('resolver must be a function');
    }
    this.state = PENDING;
    this.queue = [];
    this.outcome = void 0;
    if (resolver !== INTERNAL) {
      safelyResolveThenable(this, resolver);
    }
  }
  
  Promise.prototype["catch"] = function (onRejected) {
    return this.then(null, onRejected);
  };
  Promise.prototype.then = function (onFulfilled, onRejected) {
    if (typeof onFulfilled !== 'function' && this.state === FULFILLED ||
      typeof onRejected !== 'function' && this.state === REJECTED) {
      return this;
    }
    var promise = new this.constructor(INTERNAL);
    if (this.state !== PENDING) {
      var resolver = this.state === FULFILLED ? onFulfilled : onRejected;
      unwrap(promise, resolver, this.outcome);
    } else {
      this.queue.push(new QueueItem(promise, onFulfilled, onRejected));
    }
  
    return promise;
  };
  function QueueItem(promise, onFulfilled, onRejected) {
    this.promise = promise;
    if (typeof onFulfilled === 'function') {
      this.onFulfilled = onFulfilled;
      this.callFulfilled = this.otherCallFulfilled;
    }
    if (typeof onRejected === 'function') {
      this.onRejected = onRejected;
      this.callRejected = this.otherCallRejected;
    }
  }
  QueueItem.prototype.callFulfilled = function (value) {
    handlers.resolve(this.promise, value);
  };
  QueueItem.prototype.otherCallFulfilled = function (value) {
    unwrap(this.promise, this.onFulfilled, value);
  };
  QueueItem.prototype.callRejected = function (value) {
    handlers.reject(this.promise, value);
  };
  QueueItem.prototype.otherCallRejected = function (value) {
    unwrap(this.promise, this.onRejected, value);
  };
  
  function unwrap(promise, func, value) {
    immediate(function () {
      var returnValue;
      try {
        returnValue = func(value);
      } catch (e) {
        return handlers.reject(promise, e);
      }
      if (returnValue === promise) {
        handlers.reject(promise, new TypeError('Cannot resolve promise with itself'));
      } else {
        handlers.resolve(promise, returnValue);
      }
    });
  }
  
  handlers.resolve = function (self, value) {
    var result = tryCatch(getThen, value);
    if (result.status === 'error') {
      return handlers.reject(self, result.value);
    }
    var thenable = result.value;
  
    if (thenable) {
      safelyResolveThenable(self, thenable);
    } else {
      self.state = FULFILLED;
      self.outcome = value;
      var i = -1;
      var len = self.queue.length;
      while (++i < len) {
        self.queue[i].callFulfilled(value);
      }
    }
    return self;
  };
  handlers.reject = function (self, error) {
    self.state = REJECTED;
    self.outcome = error;
    var i = -1;
    var len = self.queue.length;
    while (++i < len) {
      self.queue[i].callRejected(error);
    }
    return self;
  };
  
  function getThen(obj) {
    // Make sure we only access the accessor once as required by the spec
    var then = obj && obj.then;
    if (obj && typeof obj === 'object' && typeof then === 'function') {
      return function appyThen() {
        then.apply(obj, arguments);
      };
    }
  }
  
  function safelyResolveThenable(self, thenable) {
    // Either fulfill, reject or reject with error
    var called = false;
    function onError(value) {
      if (called) {
        return;
      }
      called = true;
      handlers.reject(self, value);
    }
  
    function onSuccess(value) {
      if (called) {
        return;
      }
      called = true;
      handlers.resolve(self, value);
    }
  
    function tryToUnwrap() {
      thenable(onSuccess, onError);
    }
  
    var result = tryCatch(tryToUnwrap);
    if (result.status === 'error') {
      onError(result.value);
    }
  }
  
  function tryCatch(func, value) {
    var out = {};
    try {
      out.value = func(value);
      out.status = 'success';
    } catch (e) {
      out.status = 'error';
      out.value = e;
    }
    return out;
  }
  
  Promise.resolve = resolve;
  function resolve(value) {
    if (value instanceof this) {
      return value;
    }
    return handlers.resolve(new this(INTERNAL), value);
  }
  
  Promise.reject = reject;
  function reject(reason) {
    var promise = new this(INTERNAL);
    return handlers.reject(promise, reason);
  }
  
  Promise.all = all;
  function all(iterable) {
    var self = this;
    if (Object.prototype.toString.call(iterable) !== '[object Array]') {
      return this.reject(new TypeError('must be an array'));
    }
  
    var len = iterable.length;
    var called = false;
    if (!len) {
      return this.resolve([]);
    }
  
    var values = new Array(len);
    var resolved = 0;
    var i = -1;
    var promise = new this(INTERNAL);
  
    while (++i < len) {
      allResolver(iterable[i], i);
    }
    return promise;
    function allResolver(value, i) {
      self.resolve(value).then(resolveFromAll, function (error) {
        if (!called) {
          called = true;
          handlers.reject(promise, error);
        }
      });
      function resolveFromAll(outValue) {
        values[i] = outValue;
        if (++resolved === len && !called) {
          called = true;
          handlers.resolve(promise, values);
        }
      }
    }
  }
  
  Promise.race = race;
  function race(iterable) {
    var self = this;
    if (Object.prototype.toString.call(iterable) !== '[object Array]') {
      return this.reject(new TypeError('must be an array'));
    }
  
    var len = iterable.length;
    var called = false;
    if (!len) {
      return this.resolve([]);
    }
  
    var i = -1;
    var promise = new this(INTERNAL);
  
    while (++i < len) {
      resolver(iterable[i]);
    }
    return promise;
    function resolver(value) {
      self.resolve(value).then(function (response) {
        if (!called) {
          called = true;
          handlers.resolve(promise, response);
        }
      }, function (error) {
        if (!called) {
          called = true;
          handlers.reject(promise, error);
        }
      });
    }
  }
  
  },{"6":6}],10:[function(_dereq_,module,exports){
  /**
   * Helpers.
   */
  
  var s = 1000;
  var m = s * 60;
  var h = m * 60;
  var d = h * 24;
  var y = d * 365.25;
  
  /**
   * Parse or format the given `val`.
   *
   * Options:
   *
   *  - `long` verbose formatting [false]
   *
   * @param {String|Number} val
   * @param {Object} options
   * @return {String|Number}
   * @api public
   */
  
  module.exports = function(val, options){
    options = options || {};
    if ('string' == typeof val) return parse(val);
    return options.long
      ? long(val)
      : short(val);
  };
  
  /**
   * Parse the given `str` and return milliseconds.
   *
   * @param {String} str
   * @return {Number}
   * @api private
   */
  
  function parse(str) {
    str = '' + str;
    if (str.length > 10000) return;
    var match = /^((?:\d+)?\.?\d+) *(milliseconds?|msecs?|ms|seconds?|secs?|s|minutes?|mins?|m|hours?|hrs?|h|days?|d|years?|yrs?|y)?$/i.exec(str);
    if (!match) return;
    var n = parseFloat(match[1]);
    var type = (match[2] || 'ms').toLowerCase();
    switch (type) {
      case 'years':
      case 'year':
      case 'yrs':
      case 'yr':
      case 'y':
        return n * y;
      case 'days':
      case 'day':
      case 'd':
        return n * d;
      case 'hours':
      case 'hour':
      case 'hrs':
      case 'hr':
      case 'h':
        return n * h;
      case 'minutes':
      case 'minute':
      case 'mins':
      case 'min':
      case 'm':
        return n * m;
      case 'seconds':
      case 'second':
      case 'secs':
      case 'sec':
      case 's':
        return n * s;
      case 'milliseconds':
      case 'millisecond':
      case 'msecs':
      case 'msec':
      case 'ms':
        return n;
    }
  }
  
  /**
   * Short format for `ms`.
   *
   * @param {Number} ms
   * @return {String}
   * @api private
   */
  
  function short(ms) {
    if (ms >= d) return Math.round(ms / d) + 'd';
    if (ms >= h) return Math.round(ms / h) + 'h';
    if (ms >= m) return Math.round(ms / m) + 'm';
    if (ms >= s) return Math.round(ms / s) + 's';
    return ms + 'ms';
  }
  
  /**
   * Long format for `ms`.
   *
   * @param {Number} ms
   * @return {String}
   * @api private
   */
  
  function long(ms) {
    return plural(ms, d, 'day')
      || plural(ms, h, 'hour')
      || plural(ms, m, 'minute')
      || plural(ms, s, 'second')
      || ms + ' ms';
  }
  
  /**
   * Pluralization helper.
   */
  
  function plural(ms, n, name) {
    if (ms < n) return;
    if (ms < n * 1.5) return Math.floor(ms / n) + ' ' + name;
    return Math.ceil(ms / n) + ' ' + name + 's';
  }
  
  },{}],11:[function(_dereq_,module,exports){
  // shim for using process in browser
  var process = module.exports = {};
  
  // cached from whatever global is present so that test runners that stub it
  // don't break things.  But we need to wrap it in a try catch in case it is
  // wrapped in strict mode code which doesn't define any globals.  It's inside a
  // function because try/catches deoptimize in certain engines.
  
  var cachedSetTimeout;
  var cachedClearTimeout;
  
  function defaultSetTimout() {
      throw new Error('setTimeout has not been defined');
  }
  function defaultClearTimeout () {
      throw new Error('clearTimeout has not been defined');
  }
  (function () {
      try {
          if (typeof setTimeout === 'function') {
              cachedSetTimeout = setTimeout;
          } else {
              cachedSetTimeout = defaultSetTimout;
          }
      } catch (e) {
          cachedSetTimeout = defaultSetTimout;
      }
      try {
          if (typeof clearTimeout === 'function') {
              cachedClearTimeout = clearTimeout;
          } else {
              cachedClearTimeout = defaultClearTimeout;
          }
      } catch (e) {
          cachedClearTimeout = defaultClearTimeout;
      }
  } ())
  function runTimeout(fun) {
      if (cachedSetTimeout === setTimeout) {
          //normal enviroments in sane situations
          return setTimeout(fun, 0);
      }
      // if setTimeout wasn't available but was latter defined
      if ((cachedSetTimeout === defaultSetTimout || !cachedSetTimeout) && setTimeout) {
          cachedSetTimeout = setTimeout;
          return setTimeout(fun, 0);
      }
      try {
          // when when somebody has screwed with setTimeout but no I.E. maddness
          return cachedSetTimeout(fun, 0);
      } catch(e){
          try {
              // When we are in I.E. but the script has been evaled so I.E. doesn't trust the global object when called normally
              return cachedSetTimeout.call(null, fun, 0);
          } catch(e){
              // same as above but when it's a version of I.E. that must have the global object for 'this', hopfully our context correct otherwise it will throw a global error
              return cachedSetTimeout.call(this, fun, 0);
          }
      }
  
  
  }
  function runClearTimeout(marker) {
      if (cachedClearTimeout === clearTimeout) {
          //normal enviroments in sane situations
          return clearTimeout(marker);
      }
      // if clearTimeout wasn't available but was latter defined
      if ((cachedClearTimeout === defaultClearTimeout || !cachedClearTimeout) && clearTimeout) {
          cachedClearTimeout = clearTimeout;
          return clearTimeout(marker);
      }
      try {
          // when when somebody has screwed with setTimeout but no I.E. maddness
          return cachedClearTimeout(marker);
      } catch (e){
          try {
              // When we are in I.E. but the script has been evaled so I.E. doesn't  trust the global object when called normally
              return cachedClearTimeout.call(null, marker);
          } catch (e){
              // same as above but when it's a version of I.E. that must have the global object for 'this', hopfully our context correct otherwise it will throw a global error.
              // Some versions of I.E. have different rules for clearTimeout vs setTimeout
              return cachedClearTimeout.call(this, marker);
          }
      }
  
  
  
  }
  var queue = [];
  var draining = false;
  var currentQueue;
  var queueIndex = -1;
  
  function cleanUpNextTick() {
      if (!draining || !currentQueue) {
          return;
      }
      draining = false;
      if (currentQueue.length) {
          queue = currentQueue.concat(queue);
      } else {
          queueIndex = -1;
      }
      if (queue.length) {
          drainQueue();
      }
  }
  
  function drainQueue() {
      if (draining) {
          return;
      }
      var timeout = runTimeout(cleanUpNextTick);
      draining = true;
  
      var len = queue.length;
      while(len) {
          currentQueue = queue;
          queue = [];
          while (++queueIndex < len) {
              if (currentQueue) {
                  currentQueue[queueIndex].run();
              }
          }
          queueIndex = -1;
          len = queue.length;
      }
      currentQueue = null;
      draining = false;
      runClearTimeout(timeout);
  }
  
  process.nextTick = function (fun) {
      var args = new Array(arguments.length - 1);
      if (arguments.length > 1) {
          for (var i = 1; i < arguments.length; i++) {
              args[i - 1] = arguments[i];
          }
      }
      queue.push(new Item(fun, args));
      if (queue.length === 1 && !draining) {
          runTimeout(drainQueue);
      }
  };
  
  // v8 likes predictible objects
  function Item(fun, array) {
      this.fun = fun;
      this.array = array;
  }
  Item.prototype.run = function () {
      this.fun.apply(null, this.array);
  };
  process.title = 'browser';
  process.browser = true;
  process.env = {};
  process.argv = [];
  process.version = ''; // empty string to avoid regexp issues
  process.versions = {};
  
  function noop() {}
  
  process.on = noop;
  process.addListener = noop;
  process.once = noop;
  process.off = noop;
  process.removeListener = noop;
  process.removeAllListeners = noop;
  process.emit = noop;
  
  process.binding = function (name) {
      throw new Error('process.binding is not supported');
  };
  
  process.cwd = function () { return '/' };
  process.chdir = function (dir) {
      throw new Error('process.chdir is not supported');
  };
  process.umask = function() { return 0; };
  
  },{}],12:[function(_dereq_,module,exports){
  // Generated by CoffeeScript 1.9.2
  (function() {
    var hasProp = {}.hasOwnProperty,
      slice = [].slice;
  
    module.exports = function(source, scope) {
      var key, keys, value, values;
      keys = [];
      values = [];
      for (key in scope) {
        if (!hasProp.call(scope, key)) continue;
        value = scope[key];
        if (key === 'this') {
          continue;
        }
        keys.push(key);
        values.push(value);
      }
      return Function.apply(null, slice.call(keys).concat([source])).apply(scope["this"], values);
    };
  
  }).call(this);
  
  },{}],13:[function(_dereq_,module,exports){
  (function (factory) {
      if (typeof exports === 'object') {
          // Node/CommonJS
          module.exports = factory();
      } else if (typeof define === 'function' && define.amd) {
          // AMD
          define(factory);
      } else {
          // Browser globals (with support for web workers)
          var glob;
  
          try {
              glob = window;
          } catch (e) {
              glob = self;
          }
  
          glob.SparkMD5 = factory();
      }
  }(function (undefined) {
  
      'use strict';
  
      /*
       * Fastest md5 implementation around (JKM md5).
       * Credits: Joseph Myers
       *
       * @see http://www.myersdaily.org/joseph/javascript/md5-text.html
       * @see http://jsperf.com/md5-shootout/7
       */
  
      /* this function is much faster,
        so if possible we use it. Some IEs
        are the only ones I know of that
        need the idiotic second function,
        generated by an if clause.  */
      var add32 = function (a, b) {
          return (a + b) & 0xFFFFFFFF;
      },
          hex_chr = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'];
  
  
      function cmn(q, a, b, x, s, t) {
          a = add32(add32(a, q), add32(x, t));
          return add32((a << s) | (a >>> (32 - s)), b);
      }
  
      function ff(a, b, c, d, x, s, t) {
          return cmn((b & c) | ((~b) & d), a, b, x, s, t);
      }
  
      function gg(a, b, c, d, x, s, t) {
          return cmn((b & d) | (c & (~d)), a, b, x, s, t);
      }
  
      function hh(a, b, c, d, x, s, t) {
          return cmn(b ^ c ^ d, a, b, x, s, t);
      }
  
      function ii(a, b, c, d, x, s, t) {
          return cmn(c ^ (b | (~d)), a, b, x, s, t);
      }
  
      function md5cycle(x, k) {
          var a = x[0],
              b = x[1],
              c = x[2],
              d = x[3];
  
          a = ff(a, b, c, d, k[0], 7, -680876936);
          d = ff(d, a, b, c, k[1], 12, -389564586);
          c = ff(c, d, a, b, k[2], 17, 606105819);
          b = ff(b, c, d, a, k[3], 22, -1044525330);
          a = ff(a, b, c, d, k[4], 7, -176418897);
          d = ff(d, a, b, c, k[5], 12, 1200080426);
          c = ff(c, d, a, b, k[6], 17, -1473231341);
          b = ff(b, c, d, a, k[7], 22, -45705983);
          a = ff(a, b, c, d, k[8], 7, 1770035416);
          d = ff(d, a, b, c, k[9], 12, -1958414417);
          c = ff(c, d, a, b, k[10], 17, -42063);
          b = ff(b, c, d, a, k[11], 22, -1990404162);
          a = ff(a, b, c, d, k[12], 7, 1804603682);
          d = ff(d, a, b, c, k[13], 12, -40341101);
          c = ff(c, d, a, b, k[14], 17, -1502002290);
          b = ff(b, c, d, a, k[15], 22, 1236535329);
  
          a = gg(a, b, c, d, k[1], 5, -165796510);
          d = gg(d, a, b, c, k[6], 9, -1069501632);
          c = gg(c, d, a, b, k[11], 14, 643717713);
          b = gg(b, c, d, a, k[0], 20, -373897302);
          a = gg(a, b, c, d, k[5], 5, -701558691);
          d = gg(d, a, b, c, k[10], 9, 38016083);
          c = gg(c, d, a, b, k[15], 14, -660478335);
          b = gg(b, c, d, a, k[4], 20, -405537848);
          a = gg(a, b, c, d, k[9], 5, 568446438);
          d = gg(d, a, b, c, k[14], 9, -1019803690);
          c = gg(c, d, a, b, k[3], 14, -187363961);
          b = gg(b, c, d, a, k[8], 20, 1163531501);
          a = gg(a, b, c, d, k[13], 5, -1444681467);
          d = gg(d, a, b, c, k[2], 9, -51403784);
          c = gg(c, d, a, b, k[7], 14, 1735328473);
          b = gg(b, c, d, a, k[12], 20, -1926607734);
  
          a = hh(a, b, c, d, k[5], 4, -378558);
          d = hh(d, a, b, c, k[8], 11, -2022574463);
          c = hh(c, d, a, b, k[11], 16, 1839030562);
          b = hh(b, c, d, a, k[14], 23, -35309556);
          a = hh(a, b, c, d, k[1], 4, -1530992060);
          d = hh(d, a, b, c, k[4], 11, 1272893353);
          c = hh(c, d, a, b, k[7], 16, -155497632);
          b = hh(b, c, d, a, k[10], 23, -1094730640);
          a = hh(a, b, c, d, k[13], 4, 681279174);
          d = hh(d, a, b, c, k[0], 11, -358537222);
          c = hh(c, d, a, b, k[3], 16, -722521979);
          b = hh(b, c, d, a, k[6], 23, 76029189);
          a = hh(a, b, c, d, k[9], 4, -640364487);
          d = hh(d, a, b, c, k[12], 11, -421815835);
          c = hh(c, d, a, b, k[15], 16, 530742520);
          b = hh(b, c, d, a, k[2], 23, -995338651);
  
          a = ii(a, b, c, d, k[0], 6, -198630844);
          d = ii(d, a, b, c, k[7], 10, 1126891415);
          c = ii(c, d, a, b, k[14], 15, -1416354905);
          b = ii(b, c, d, a, k[5], 21, -57434055);
          a = ii(a, b, c, d, k[12], 6, 1700485571);
          d = ii(d, a, b, c, k[3], 10, -1894986606);
          c = ii(c, d, a, b, k[10], 15, -1051523);
          b = ii(b, c, d, a, k[1], 21, -2054922799);
          a = ii(a, b, c, d, k[8], 6, 1873313359);
          d = ii(d, a, b, c, k[15], 10, -30611744);
          c = ii(c, d, a, b, k[6], 15, -1560198380);
          b = ii(b, c, d, a, k[13], 21, 1309151649);
          a = ii(a, b, c, d, k[4], 6, -145523070);
          d = ii(d, a, b, c, k[11], 10, -1120210379);
          c = ii(c, d, a, b, k[2], 15, 718787259);
          b = ii(b, c, d, a, k[9], 21, -343485551);
  
          x[0] = add32(a, x[0]);
          x[1] = add32(b, x[1]);
          x[2] = add32(c, x[2]);
          x[3] = add32(d, x[3]);
      }
  
      function md5blk(s) {
          var md5blks = [],
              i; /* Andy King said do it this way. */
  
          for (i = 0; i < 64; i += 4) {
              md5blks[i >> 2] = s.charCodeAt(i) + (s.charCodeAt(i + 1) << 8) + (s.charCodeAt(i + 2) << 16) + (s.charCodeAt(i + 3) << 24);
          }
          return md5blks;
      }
  
      function md5blk_array(a) {
          var md5blks = [],
              i; /* Andy King said do it this way. */
  
          for (i = 0; i < 64; i += 4) {
              md5blks[i >> 2] = a[i] + (a[i + 1] << 8) + (a[i + 2] << 16) + (a[i + 3] << 24);
          }
          return md5blks;
      }
  
      function md51(s) {
          var n = s.length,
              state = [1732584193, -271733879, -1732584194, 271733878],
              i,
              length,
              tail,
              tmp,
              lo,
              hi;
  
          for (i = 64; i <= n; i += 64) {
              md5cycle(state, md5blk(s.substring(i - 64, i)));
          }
          s = s.substring(i - 64);
          length = s.length;
          tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
          for (i = 0; i < length; i += 1) {
              tail[i >> 2] |= s.charCodeAt(i) << ((i % 4) << 3);
          }
          tail[i >> 2] |= 0x80 << ((i % 4) << 3);
          if (i > 55) {
              md5cycle(state, tail);
              for (i = 0; i < 16; i += 1) {
                  tail[i] = 0;
              }
          }
  
          // Beware that the final length might not fit in 32 bits so we take care of that
          tmp = n * 8;
          tmp = tmp.toString(16).match(/(.*?)(.{0,8})$/);
          lo = parseInt(tmp[2], 16);
          hi = parseInt(tmp[1], 16) || 0;
  
          tail[14] = lo;
          tail[15] = hi;
  
          md5cycle(state, tail);
          return state;
      }
  
      function md51_array(a) {
          var n = a.length,
              state = [1732584193, -271733879, -1732584194, 271733878],
              i,
              length,
              tail,
              tmp,
              lo,
              hi;
  
          for (i = 64; i <= n; i += 64) {
              md5cycle(state, md5blk_array(a.subarray(i - 64, i)));
          }
  
          // Not sure if it is a bug, however IE10 will always produce a sub array of length 1
          // containing the last element of the parent array if the sub array specified starts
          // beyond the length of the parent array - weird.
          // https://connect.microsoft.com/IE/feedback/details/771452/typed-array-subarray-issue
          a = (i - 64) < n ? a.subarray(i - 64) : new Uint8Array(0);
  
          length = a.length;
          tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
          for (i = 0; i < length; i += 1) {
              tail[i >> 2] |= a[i] << ((i % 4) << 3);
          }
  
          tail[i >> 2] |= 0x80 << ((i % 4) << 3);
          if (i > 55) {
              md5cycle(state, tail);
              for (i = 0; i < 16; i += 1) {
                  tail[i] = 0;
              }
          }
  
          // Beware that the final length might not fit in 32 bits so we take care of that
          tmp = n * 8;
          tmp = tmp.toString(16).match(/(.*?)(.{0,8})$/);
          lo = parseInt(tmp[2], 16);
          hi = parseInt(tmp[1], 16) || 0;
  
          tail[14] = lo;
          tail[15] = hi;
  
          md5cycle(state, tail);
  
          return state;
      }
  
      function rhex(n) {
          var s = '',
              j;
          for (j = 0; j < 4; j += 1) {
              s += hex_chr[(n >> (j * 8 + 4)) & 0x0F] + hex_chr[(n >> (j * 8)) & 0x0F];
          }
          return s;
      }
  
      function hex(x) {
          var i;
          for (i = 0; i < x.length; i += 1) {
              x[i] = rhex(x[i]);
          }
          return x.join('');
      }
  
      // In some cases the fast add32 function cannot be used..
      if (hex(md51('hello')) !== '5d41402abc4b2a76b9719d911017c592') {
          add32 = function (x, y) {
              var lsw = (x & 0xFFFF) + (y & 0xFFFF),
                  msw = (x >> 16) + (y >> 16) + (lsw >> 16);
              return (msw << 16) | (lsw & 0xFFFF);
          };
      }
  
      // ---------------------------------------------------
  
      /**
       * ArrayBuffer slice polyfill.
       *
       * @see https://github.com/ttaubert/node-arraybuffer-slice
       */
  
      if (typeof ArrayBuffer !== 'undefined' && !ArrayBuffer.prototype.slice) {
          (function () {
              function clamp(val, length) {
                  val = (val | 0) || 0;
  
                  if (val < 0) {
                      return Math.max(val + length, 0);
                  }
  
                  return Math.min(val, length);
              }
  
              ArrayBuffer.prototype.slice = function (from, to) {
                  var length = this.byteLength,
                      begin = clamp(from, length),
                      end = length,
                      num,
                      target,
                      targetArray,
                      sourceArray;
  
                  if (to !== undefined) {
                      end = clamp(to, length);
                  }
  
                  if (begin > end) {
                      return new ArrayBuffer(0);
                  }
  
                  num = end - begin;
                  target = new ArrayBuffer(num);
                  targetArray = new Uint8Array(target);
  
                  sourceArray = new Uint8Array(this, begin, num);
                  targetArray.set(sourceArray);
  
                  return target;
              };
          })();
      }
  
      // ---------------------------------------------------
  
      /**
       * Helpers.
       */
  
      function toUtf8(str) {
          if (/[\u0080-\uFFFF]/.test(str)) {
              str = unescape(encodeURIComponent(str));
          }
  
          return str;
      }
  
      function utf8Str2ArrayBuffer(str, returnUInt8Array) {
          var length = str.length,
             buff = new ArrayBuffer(length),
             arr = new Uint8Array(buff),
             i;
  
          for (i = 0; i < length; i += 1) {
              arr[i] = str.charCodeAt(i);
          }
  
          return returnUInt8Array ? arr : buff;
      }
  
      function arrayBuffer2Utf8Str(buff) {
          return String.fromCharCode.apply(null, new Uint8Array(buff));
      }
  
      function concatenateArrayBuffers(first, second, returnUInt8Array) {
          var result = new Uint8Array(first.byteLength + second.byteLength);
  
          result.set(new Uint8Array(first));
          result.set(new Uint8Array(second), first.byteLength);
  
          return returnUInt8Array ? result : result.buffer;
      }
  
      function hexToBinaryString(hex) {
          var bytes = [],
              length = hex.length,
              x;
  
          for (x = 0; x < length - 1; x += 2) {
              bytes.push(parseInt(hex.substr(x, 2), 16));
          }
  
          return String.fromCharCode.apply(String, bytes);
      }
  
      // ---------------------------------------------------
  
      /**
       * SparkMD5 OOP implementation.
       *
       * Use this class to perform an incremental md5, otherwise use the
       * static methods instead.
       */
  
      function SparkMD5() {
          // call reset to init the instance
          this.reset();
      }
  
      /**
       * Appends a string.
       * A conversion will be applied if an utf8 string is detected.
       *
       * @param {String} str The string to be appended
       *
       * @return {SparkMD5} The instance itself
       */
      SparkMD5.prototype.append = function (str) {
          // Converts the string to utf8 bytes if necessary
          // Then append as binary
          this.appendBinary(toUtf8(str));
  
          return this;
      };
  
      /**
       * Appends a binary string.
       *
       * @param {String} contents The binary string to be appended
       *
       * @return {SparkMD5} The instance itself
       */
      SparkMD5.prototype.appendBinary = function (contents) {
          this._buff += contents;
          this._length += contents.length;
  
          var length = this._buff.length,
              i;
  
          for (i = 64; i <= length; i += 64) {
              md5cycle(this._hash, md5blk(this._buff.substring(i - 64, i)));
          }
  
          this._buff = this._buff.substring(i - 64);
  
          return this;
      };
  
      /**
       * Finishes the incremental computation, reseting the internal state and
       * returning the result.
       *
       * @param {Boolean} raw True to get the raw string, false to get the hex string
       *
       * @return {String} The result
       */
      SparkMD5.prototype.end = function (raw) {
          var buff = this._buff,
              length = buff.length,
              i,
              tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
              ret;
  
          for (i = 0; i < length; i += 1) {
              tail[i >> 2] |= buff.charCodeAt(i) << ((i % 4) << 3);
          }
  
          this._finish(tail, length);
          ret = hex(this._hash);
  
          if (raw) {
              ret = hexToBinaryString(ret);
          }
  
          this.reset();
  
          return ret;
      };
  
      /**
       * Resets the internal state of the computation.
       *
       * @return {SparkMD5} The instance itself
       */
      SparkMD5.prototype.reset = function () {
          this._buff = '';
          this._length = 0;
          this._hash = [1732584193, -271733879, -1732584194, 271733878];
  
          return this;
      };
  
      /**
       * Gets the internal state of the computation.
       *
       * @return {Object} The state
       */
      SparkMD5.prototype.getState = function () {
          return {
              buff: this._buff,
              length: this._length,
              hash: this._hash
          };
      };
  
      /**
       * Gets the internal state of the computation.
       *
       * @param {Object} state The state
       *
       * @return {SparkMD5} The instance itself
       */
      SparkMD5.prototype.setState = function (state) {
          this._buff = state.buff;
          this._length = state.length;
          this._hash = state.hash;
  
          return this;
      };
  
      /**
       * Releases memory used by the incremental buffer and other additional
       * resources. If you plan to use the instance again, use reset instead.
       */
      SparkMD5.prototype.destroy = function () {
          delete this._hash;
          delete this._buff;
          delete this._length;
      };
  
      /**
       * Finish the final calculation based on the tail.
       *
       * @param {Array}  tail   The tail (will be modified)
       * @param {Number} length The length of the remaining buffer
       */
      SparkMD5.prototype._finish = function (tail, length) {
          var i = length,
              tmp,
              lo,
              hi;
  
          tail[i >> 2] |= 0x80 << ((i % 4) << 3);
          if (i > 55) {
              md5cycle(this._hash, tail);
              for (i = 0; i < 16; i += 1) {
                  tail[i] = 0;
              }
          }
  
          // Do the final computation based on the tail and length
          // Beware that the final length may not fit in 32 bits so we take care of that
          tmp = this._length * 8;
          tmp = tmp.toString(16).match(/(.*?)(.{0,8})$/);
          lo = parseInt(tmp[2], 16);
          hi = parseInt(tmp[1], 16) || 0;
  
          tail[14] = lo;
          tail[15] = hi;
          md5cycle(this._hash, tail);
      };
  
      /**
       * Performs the md5 hash on a string.
       * A conversion will be applied if utf8 string is detected.
       *
       * @param {String}  str The string
       * @param {Boolean} raw True to get the raw string, false to get the hex string
       *
       * @return {String} The result
       */
      SparkMD5.hash = function (str, raw) {
          // Converts the string to utf8 bytes if necessary
          // Then compute it using the binary function
          return SparkMD5.hashBinary(toUtf8(str), raw);
      };
  
      /**
       * Performs the md5 hash on a binary string.
       *
       * @param {String}  content The binary string
       * @param {Boolean} raw     True to get the raw string, false to get the hex string
       *
       * @return {String} The result
       */
      SparkMD5.hashBinary = function (content, raw) {
          var hash = md51(content),
              ret = hex(hash);
  
          return raw ? hexToBinaryString(ret) : ret;
      };
  
      // ---------------------------------------------------
  
      /**
       * SparkMD5 OOP implementation for array buffers.
       *
       * Use this class to perform an incremental md5 ONLY for array buffers.
       */
      SparkMD5.ArrayBuffer = function () {
          // call reset to init the instance
          this.reset();
      };
  
      /**
       * Appends an array buffer.
       *
       * @param {ArrayBuffer} arr The array to be appended
       *
       * @return {SparkMD5.ArrayBuffer} The instance itself
       */
      SparkMD5.ArrayBuffer.prototype.append = function (arr) {
          var buff = concatenateArrayBuffers(this._buff.buffer, arr, true),
              length = buff.length,
              i;
  
          this._length += arr.byteLength;
  
          for (i = 64; i <= length; i += 64) {
              md5cycle(this._hash, md5blk_array(buff.subarray(i - 64, i)));
          }
  
          this._buff = (i - 64) < length ? new Uint8Array(buff.buffer.slice(i - 64)) : new Uint8Array(0);
  
          return this;
      };
  
      /**
       * Finishes the incremental computation, reseting the internal state and
       * returning the result.
       *
       * @param {Boolean} raw True to get the raw string, false to get the hex string
       *
       * @return {String} The result
       */
      SparkMD5.ArrayBuffer.prototype.end = function (raw) {
          var buff = this._buff,
              length = buff.length,
              tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
              i,
              ret;
  
          for (i = 0; i < length; i += 1) {
              tail[i >> 2] |= buff[i] << ((i % 4) << 3);
          }
  
          this._finish(tail, length);
          ret = hex(this._hash);
  
          if (raw) {
              ret = hexToBinaryString(ret);
          }
  
          this.reset();
  
          return ret;
      };
  
      /**
       * Resets the internal state of the computation.
       *
       * @return {SparkMD5.ArrayBuffer} The instance itself
       */
      SparkMD5.ArrayBuffer.prototype.reset = function () {
          this._buff = new Uint8Array(0);
          this._length = 0;
          this._hash = [1732584193, -271733879, -1732584194, 271733878];
  
          return this;
      };
  
      /**
       * Gets the internal state of the computation.
       *
       * @return {Object} The state
       */
      SparkMD5.ArrayBuffer.prototype.getState = function () {
          var state = SparkMD5.prototype.getState.call(this);
  
          // Convert buffer to a string
          state.buff = arrayBuffer2Utf8Str(state.buff);
  
          return state;
      };
  
      /**
       * Gets the internal state of the computation.
       *
       * @param {Object} state The state
       *
       * @return {SparkMD5.ArrayBuffer} The instance itself
       */
      SparkMD5.ArrayBuffer.prototype.setState = function (state) {
          // Convert string to buffer
          state.buff = utf8Str2ArrayBuffer(state.buff, true);
  
          return SparkMD5.prototype.setState.call(this, state);
      };
  
      SparkMD5.ArrayBuffer.prototype.destroy = SparkMD5.prototype.destroy;
  
      SparkMD5.ArrayBuffer.prototype._finish = SparkMD5.prototype._finish;
  
      /**
       * Performs the md5 hash on an array buffer.
       *
       * @param {ArrayBuffer} arr The array buffer
       * @param {Boolean}     raw True to get the raw string, false to get the hex one
       *
       * @return {String} The result
       */
      SparkMD5.ArrayBuffer.hash = function (arr, raw) {
          var hash = md51_array(new Uint8Array(arr)),
              ret = hex(hash);
  
          return raw ? hexToBinaryString(ret) : ret;
      };
  
      return SparkMD5;
  }));
  
  },{}],14:[function(_dereq_,module,exports){
  'use strict';
  
  /**
   * Stringify/parse functions that don't operate
   * recursively, so they avoid call stack exceeded
   * errors.
   */
  exports.stringify = function stringify(input) {
    var queue = [];
    queue.push({obj: input});
  
    var res = '';
    var next, obj, prefix, val, i, arrayPrefix, keys, k, key, value, objPrefix;
    while ((next = queue.pop())) {
      obj = next.obj;
      prefix = next.prefix || '';
      val = next.val || '';
      res += prefix;
      if (val) {
        res += val;
      } else if (typeof obj !== 'object') {
        res += typeof obj === 'undefined' ? null : JSON.stringify(obj);
      } else if (obj === null) {
        res += 'null';
      } else if (Array.isArray(obj)) {
        queue.push({val: ']'});
        for (i = obj.length - 1; i >= 0; i--) {
          arrayPrefix = i === 0 ? '' : ',';
          queue.push({obj: obj[i], prefix: arrayPrefix});
        }
        queue.push({val: '['});
      } else { // object
        keys = [];
        for (k in obj) {
          if (obj.hasOwnProperty(k)) {
            keys.push(k);
          }
        }
        queue.push({val: '}'});
        for (i = keys.length - 1; i >= 0; i--) {
          key = keys[i];
          value = obj[key];
          objPrefix = (i > 0 ? ',' : '');
          objPrefix += JSON.stringify(key) + ':';
          queue.push({obj: value, prefix: objPrefix});
        }
        queue.push({val: '{'});
      }
    }
    return res;
  };
  
  // Convenience function for the parse function.
  // This pop function is basically copied from
  // pouchCollate.parseIndexableString
  function pop(obj, stack, metaStack) {
    var lastMetaElement = metaStack[metaStack.length - 1];
    if (obj === lastMetaElement.element) {
      // popping a meta-element, e.g. an object whose value is another object
      metaStack.pop();
      lastMetaElement = metaStack[metaStack.length - 1];
    }
    var element = lastMetaElement.element;
    var lastElementIndex = lastMetaElement.index;
    if (Array.isArray(element)) {
      element.push(obj);
    } else if (lastElementIndex === stack.length - 2) { // obj with key+value
      var key = stack.pop();
      element[key] = obj;
    } else {
      stack.push(obj); // obj with key only
    }
  }
  
  exports.parse = function (str) {
    var stack = [];
    var metaStack = []; // stack for arrays and objects
    var i = 0;
    var collationIndex,parsedNum,numChar;
    var parsedString,lastCh,numConsecutiveSlashes,ch;
    var arrayElement, objElement;
    while (true) {
      collationIndex = str[i++];
      if (collationIndex === '}' ||
          collationIndex === ']' ||
          typeof collationIndex === 'undefined') {
        if (stack.length === 1) {
          return stack.pop();
        } else {
          pop(stack.pop(), stack, metaStack);
          continue;
        }
      }
      switch (collationIndex) {
        case ' ':
        case '\t':
        case '\n':
        case ':':
        case ',':
          break;
        case 'n':
          i += 3; // 'ull'
          pop(null, stack, metaStack);
          break;
        case 't':
          i += 3; // 'rue'
          pop(true, stack, metaStack);
          break;
        case 'f':
          i += 4; // 'alse'
          pop(false, stack, metaStack);
          break;
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
        case '-':
          parsedNum = '';
          i--;
          while (true) {
            numChar = str[i++];
            if (/[\d\.\-e\+]/.test(numChar)) {
              parsedNum += numChar;
            } else {
              i--;
              break;
            }
          }
          pop(parseFloat(parsedNum), stack, metaStack);
          break;
        case '"':
          parsedString = '';
          lastCh = void 0;
          numConsecutiveSlashes = 0;
          while (true) {
            ch = str[i++];
            if (ch !== '"' || (lastCh === '\\' &&
                numConsecutiveSlashes % 2 === 1)) {
              parsedString += ch;
              lastCh = ch;
              if (lastCh === '\\') {
                numConsecutiveSlashes++;
              } else {
                numConsecutiveSlashes = 0;
              }
            } else {
              break;
            }
          }
          pop(JSON.parse('"' + parsedString + '"'), stack, metaStack);
          break;
        case '[':
          arrayElement = { element: [], index: stack.length };
          stack.push(arrayElement.element);
          metaStack.push(arrayElement);
          break;
        case '{':
          objElement = { element: {}, index: stack.length };
          stack.push(objElement.element);
          metaStack.push(objElement);
          break;
        default:
          throw new Error(
            'unexpectedly reached end of input: ' + collationIndex);
      }
    }
  };
  
  },{}],15:[function(_dereq_,module,exports){
  (function (process,global){
  'use strict';
  
  function _interopDefault (ex) { return (ex && (typeof ex === 'object') && 'default' in ex) ? ex['default'] : ex; }
  
  var jsExtend = _dereq_(8);
  var debug = _interopDefault(_dereq_(2));
  var inherits = _interopDefault(_dereq_(7));
  var lie = _interopDefault(_dereq_(9));
  var events = _dereq_(5);
  var getArguments = _interopDefault(_dereq_(1));
  var scopedEval = _interopDefault(_dereq_(12));
  var Md5 = _interopDefault(_dereq_(13));
  var vuvuzela = _interopDefault(_dereq_(14));
  var PromisePool = _interopDefault(_dereq_(4));
  
  /* istanbul ignore next */
  var PouchPromise = typeof Promise === 'function' ? Promise : lie;
  
  // based on https://github.com/montagejs/collections
  function mangle(key) {
    return '$' + key;
  }
  function unmangle(key) {
    return key.substring(1);
  }
  function _Map() {
    this.store = {};
  }
  _Map.prototype.get = function (key) {
    var mangled = mangle(key);
    return this.store[mangled];
  };
  _Map.prototype.set = function (key, value) {
    var mangled = mangle(key);
    this.store[mangled] = value;
    return true;
  };
  _Map.prototype.has = function (key) {
    var mangled = mangle(key);
    return mangled in this.store;
  };
  _Map.prototype["delete"] = function (key) {
    var mangled = mangle(key);
    var res = mangled in this.store;
    delete this.store[mangled];
    return res;
  };
  _Map.prototype.forEach = function (cb) {
    var keys = Object.keys(this.store);
    for (var i = 0, len = keys.length; i < len; i++) {
      var key = keys[i];
      var value = this.store[key];
      key = unmangle(key);
      cb(value, key);
    }
  };
  
  function _Set(array) {
    this.store = new _Map();
  
    // init with an array
    if (array && Array.isArray(array)) {
      for (var i = 0, len = array.length; i < len; i++) {
        this.add(array[i]);
      }
    }
  }
  _Set.prototype.add = function (key) {
    return this.store.set(key, true);
  };
  _Set.prototype.has = function (key) {
    return this.store.has(key);
  };
  
  function isBinaryObject(object) {
    return (typeof ArrayBuffer !== 'undefined' && object instanceof ArrayBuffer) ||
      (typeof Blob !== 'undefined' && object instanceof Blob);
  }
  
  function cloneArrayBuffer(buff) {
    if (typeof buff.slice === 'function') {
      return buff.slice(0);
    }
    // IE10-11 slice() polyfill
    var target = new ArrayBuffer(buff.byteLength);
    var targetArray = new Uint8Array(target);
    var sourceArray = new Uint8Array(buff);
    targetArray.set(sourceArray);
    return target;
  }
  
  function cloneBinaryObject(object) {
    if (object instanceof ArrayBuffer) {
      return cloneArrayBuffer(object);
    }
    var size = object.size;
    var type = object.type;
    // Blob
    if (typeof object.slice === 'function') {
      return object.slice(0, size, type);
    }
    // PhantomJS slice() replacement
    return object.webkitSlice(0, size, type);
  }
  
  // most of this is borrowed from lodash.isPlainObject:
  // https://github.com/fis-components/lodash.isplainobject/
  // blob/29c358140a74f252aeb08c9eb28bef86f2217d4a/index.js
  
  var funcToString = Function.prototype.toString;
  var objectCtorString = funcToString.call(Object);
  
  function isPlainObject(value) {
    var proto = Object.getPrototypeOf(value);
    /* istanbul ignore if */
    if (proto === null) { // not sure when this happens, but I guess it can
      return true;
    }
    var Ctor = proto.constructor;
    return (typeof Ctor == 'function' &&
      Ctor instanceof Ctor && funcToString.call(Ctor) == objectCtorString);
  }
  
  function clone(object) {
    var newObject;
    var i;
    var len;
  
    if (!object || typeof object !== 'object') {
      return object;
    }
  
    if (Array.isArray(object)) {
      newObject = [];
      for (i = 0, len = object.length; i < len; i++) {
        newObject[i] = clone(object[i]);
      }
      return newObject;
    }
  
    // special case: to avoid inconsistencies between IndexedDB
    // and other backends, we automatically stringify Dates
    if (object instanceof Date) {
      return object.toISOString();
    }
  
    if (isBinaryObject(object)) {
      return cloneBinaryObject(object);
    }
  
    if (!isPlainObject(object)) {
      return object; // don't clone objects like Workers
    }
  
    newObject = {};
    for (i in object) {
      /* istanbul ignore else */
      if (Object.prototype.hasOwnProperty.call(object, i)) {
        var value = clone(object[i]);
        if (typeof value !== 'undefined') {
          newObject[i] = value;
        }
      }
    }
    return newObject;
  }
  
  function once(fun) {
    var called = false;
    return getArguments(function (args) {
      /* istanbul ignore if */
      if (called) {
        // this is a smoke test and should never actually happen
        throw new Error('once called more than once');
      } else {
        called = true;
        fun.apply(this, args);
      }
    });
  }
  
  function toPromise(func) {
    //create the function we will be returning
    return getArguments(function (args) {
      // Clone arguments
      args = clone(args);
      var self = this;
      var tempCB =
        (typeof args[args.length - 1] === 'function') ? args.pop() : false;
      // if the last argument is a function, assume its a callback
      var usedCB;
      if (tempCB) {
        // if it was a callback, create a new callback which calls it,
        // but do so async so we don't trap any errors
        usedCB = function (err, resp) {
          process.nextTick(function () {
            tempCB(err, resp);
          });
        };
      }
      var promise = new PouchPromise(function (fulfill, reject) {
        var resp;
        try {
          var callback = once(function (err, mesg) {
            if (err) {
              reject(err);
            } else {
              fulfill(mesg);
            }
          });
          // create a callback for this invocation
          // apply the function in the orig context
          args.push(callback);
          resp = func.apply(self, args);
          if (resp && typeof resp.then === 'function') {
            fulfill(resp);
          }
        } catch (e) {
          reject(e);
        }
      });
      // if there is a callback, call it back
      if (usedCB) {
        promise.then(function (result) {
          usedCB(null, result);
        }, usedCB);
      }
      return promise;
    });
  }
  
  var log = debug('pouchdb:api');
  
  function adapterFun(name, callback) {
    function logApiCall(self, name, args) {
      /* istanbul ignore if */
      if (log.enabled) {
        var logArgs = [self.name, name];
        for (var i = 0; i < args.length - 1; i++) {
          logArgs.push(args[i]);
        }
        log.apply(null, logArgs);
  
        // override the callback itself to log the response
        var origCallback = args[args.length - 1];
        args[args.length - 1] = function (err, res) {
          var responseArgs = [self.name, name];
          responseArgs = responseArgs.concat(
            err ? ['error', err] : ['success', res]
          );
          log.apply(null, responseArgs);
          origCallback(err, res);
        };
      }
    }
  
    return toPromise(getArguments(function (args) {
      if (this._closed) {
        return PouchPromise.reject(new Error('database is closed'));
      }
      if (this._destroyed) {
        return PouchPromise.reject(new Error('database is destroyed'));
      }
      var self = this;
      logApiCall(self, name, args);
      if (!this.taskqueue.isReady) {
        return new PouchPromise(function (fulfill, reject) {
          self.taskqueue.addTask(function (failed) {
            if (failed) {
              reject(failed);
            } else {
              fulfill(self[name].apply(self, args));
            }
          });
        });
      }
      return callback.apply(this, args);
    }));
  }
  
  // like underscore/lodash _.pick()
  function pick(obj, arr) {
    var res = {};
    for (var i = 0, len = arr.length; i < len; i++) {
      var prop = arr[i];
      if (prop in obj) {
        res[prop] = obj[prop];
      }
    }
    return res;
  }
  
  // Most browsers throttle concurrent requests at 6, so it's silly
  // to shim _bulk_get by trying to launch potentially hundreds of requests
  // and then letting the majority time out. We can handle this ourselves.
  var MAX_NUM_CONCURRENT_REQUESTS = 6;
  
  function identityFunction(x) {
    return x;
  }
  
  function formatResultForOpenRevsGet(result) {
    return [{
      ok: result
    }];
  }
  
  // shim for P/CouchDB adapters that don't directly implement _bulk_get
  function bulkGet(db, opts, callback) {
    var requests = opts.docs;
  
    // consolidate into one request per doc if possible
    var requestsById = {};
    requests.forEach(function (request) {
      if (request.id in requestsById) {
        requestsById[request.id].push(request);
      } else {
        requestsById[request.id] = [request];
      }
    });
  
    var numDocs = Object.keys(requestsById).length;
    var numDone = 0;
    var perDocResults = new Array(numDocs);
  
    function collapseResultsAndFinish() {
      var results = [];
      perDocResults.forEach(function (res) {
        res.docs.forEach(function (info) {
          results.push({
            id: res.id,
            docs: [info]
          });
        });
      });
      callback(null, {results: results});
    }
  
    function checkDone() {
      if (++numDone === numDocs) {
        collapseResultsAndFinish();
      }
    }
  
    function gotResult(docIndex, id, docs) {
      perDocResults[docIndex] = {id: id, docs: docs};
      checkDone();
    }
  
    var allRequests = Object.keys(requestsById);
  
    var i = 0;
  
    function nextBatch() {
  
      if (i >= allRequests.length) {
        return;
      }
  
      var upTo = Math.min(i + MAX_NUM_CONCURRENT_REQUESTS, allRequests.length);
      var batch = allRequests.slice(i, upTo);
      processBatch(batch, i);
      i += batch.length;
    }
  
    function processBatch(batch, offset) {
      batch.forEach(function (docId, j) {
        var docIdx = offset + j;
        var docRequests = requestsById[docId];
  
        // just use the first request as the "template"
        // TODO: The _bulk_get API allows for more subtle use cases than this,
        // but for now it is unlikely that there will be a mix of different
        // "atts_since" or "attachments" in the same request, since it's just
        // replicate.js that is using this for the moment.
        // Also, atts_since is aspirational, since we don't support it yet.
        var docOpts = pick(docRequests[0], ['atts_since', 'attachments']);
        docOpts.open_revs = docRequests.map(function (request) {
          // rev is optional, open_revs disallowed
          return request.rev;
        });
  
        // remove falsey / undefined revisions
        docOpts.open_revs = docOpts.open_revs.filter(identityFunction);
  
        var formatResult = identityFunction;
  
        if (docOpts.open_revs.length === 0) {
          delete docOpts.open_revs;
  
          // when fetching only the "winning" leaf,
          // transform the result so it looks like an open_revs
          // request
          formatResult = formatResultForOpenRevsGet;
        }
  
        // globally-supplied options
        ['revs', 'attachments', 'binary', 'ajax'].forEach(function (param) {
          if (param in opts) {
            docOpts[param] = opts[param];
          }
        });
        db.get(docId, docOpts, function (err, res) {
          var result;
          /* istanbul ignore if */
          if (err) {
            result = [{error: err}];
          } else {
            result = formatResult(res);
          }
          gotResult(docIdx, docId, result);
          nextBatch();
        });
      });
    }
  
    nextBatch();
  
  }
  
  function isChromeApp() {
    return (typeof chrome !== "undefined" &&
      typeof chrome.storage !== "undefined" &&
      typeof chrome.storage.local !== "undefined");
  }
  
  var hasLocal;
  
  if (isChromeApp()) {
    hasLocal = false;
  } else {
    try {
      localStorage.setItem('_pouch_check_localstorage', 1);
      hasLocal = !!localStorage.getItem('_pouch_check_localstorage');
    } catch (e) {
      hasLocal = false;
    }
  }
  
  function hasLocalStorage() {
    return hasLocal;
  }
  
  inherits(Changes$1, events.EventEmitter);
  
  /* istanbul ignore next */
  function attachBrowserEvents(self) {
    if (isChromeApp()) {
      chrome.storage.onChanged.addListener(function (e) {
        // make sure it's event addressed to us
        if (e.db_name != null) {
          //object only has oldValue, newValue members
          self.emit(e.dbName.newValue);
        }
      });
    } else if (hasLocalStorage()) {
      if (typeof addEventListener !== 'undefined') {
        addEventListener("storage", function (e) {
          self.emit(e.key);
        });
      } else { // old IE
        window.attachEvent("storage", function (e) {
          self.emit(e.key);
        });
      }
    }
  }
  
  function Changes$1() {
    events.EventEmitter.call(this);
    this._listeners = {};
  
    attachBrowserEvents(this);
  }
  Changes$1.prototype.addListener = function (dbName, id, db, opts) {
    /* istanbul ignore if */
    if (this._listeners[id]) {
      return;
    }
    var self = this;
    var inprogress = false;
    function eventFunction() {
      /* istanbul ignore if */
      if (!self._listeners[id]) {
        return;
      }
      if (inprogress) {
        inprogress = 'waiting';
        return;
      }
      inprogress = true;
      var changesOpts = pick(opts, [
        'style', 'include_docs', 'attachments', 'conflicts', 'filter',
        'doc_ids', 'view', 'since', 'query_params', 'binary'
      ]);
  
      /* istanbul ignore next */
      function onError() {
        inprogress = false;
      }
  
      db.changes(changesOpts).on('change', function (c) {
        if (c.seq > opts.since && !opts.cancelled) {
          opts.since = c.seq;
          opts.onChange(c);
        }
      }).on('complete', function () {
        if (inprogress === 'waiting') {
          setTimeout(function (){
            eventFunction();
          },0);
        }
        inprogress = false;
      }).on('error', onError);
    }
    this._listeners[id] = eventFunction;
    this.on(dbName, eventFunction);
  };
  
  Changes$1.prototype.removeListener = function (dbName, id) {
    /* istanbul ignore if */
    if (!(id in this._listeners)) {
      return;
    }
    events.EventEmitter.prototype.removeListener.call(this, dbName,
      this._listeners[id]);
    delete this._listeners[id];
  };
  
  
  /* istanbul ignore next */
  Changes$1.prototype.notifyLocalWindows = function (dbName) {
    //do a useless change on a storage thing
    //in order to get other windows's listeners to activate
    if (isChromeApp()) {
      chrome.storage.local.set({dbName: dbName});
    } else if (hasLocalStorage()) {
      localStorage[dbName] = (localStorage[dbName] === "a") ? "b" : "a";
    }
  };
  
  Changes$1.prototype.notify = function (dbName) {
    this.emit(dbName);
    this.notifyLocalWindows(dbName);
  };
  
  function guardedConsole(method) {
    /* istanbul ignore else */
    if (console !== 'undefined' && method in console) {
      var args = Array.prototype.slice.call(arguments, 1);
      console[method].apply(console, args);
    }
  }
  
  function randomNumber(min, max) {
    var maxTimeout = 600000; // Hard-coded default of 10 minutes
    min = parseInt(min, 10) || 0;
    max = parseInt(max, 10);
    if (max !== max || max <= min) {
      max = (min || 1) << 1; //doubling
    } else {
      max = max + 1;
    }
    // In order to not exceed maxTimeout, pick a random value between half of maxTimeout and maxTimeout
    if(max > maxTimeout) {
      min = maxTimeout >> 1; // divide by two
      max = maxTimeout;
    }
    var ratio = Math.random();
    var range = max - min;
  
    return ~~(range * ratio + min); // ~~ coerces to an int, but fast.
  }
  
  function defaultBackOff(min) {
    var max = 0;
    if (!min) {
      max = 2000;
    }
    return randomNumber(min, max);
  }
  
  // designed to give info to browser users, who are disturbed
  // when they see http errors in the console
  function explainError(status, str) {
    guardedConsole('info', 'The above ' + status + ' is totally normal. ' + str);
  }
  
  inherits(PouchError, Error);
  
  function PouchError(opts) {
    Error.call(this, opts.reason);
    this.status = opts.status;
    this.name = opts.error;
    this.message = opts.reason;
    this.error = true;
  }
  
  PouchError.prototype.toString = function () {
    return JSON.stringify({
      status: this.status,
      name: this.name,
      message: this.message,
      reason: this.reason
    });
  };
  
  var UNAUTHORIZED = new PouchError({
    status: 401,
    error: 'unauthorized',
    reason: "Name or password is incorrect."
  });
  
  var MISSING_BULK_DOCS = new PouchError({
    status: 400,
    error: 'bad_request',
    reason: "Missing JSON list of 'docs'"
  });
  
  var MISSING_DOC = new PouchError({
    status: 404,
    error: 'not_found',
    reason: 'missing'
  });
  
  var REV_CONFLICT = new PouchError({
    status: 409,
    error: 'conflict',
    reason: 'Document update conflict'
  });
  
  var INVALID_ID = new PouchError({
    status: 400,
    error: 'bad_request',
    reason: '_id field must contain a string'
  });
  
  var MISSING_ID = new PouchError({
    status: 412,
    error: 'missing_id',
    reason: '_id is required for puts'
  });
  
  var RESERVED_ID = new PouchError({
    status: 400,
    error: 'bad_request',
    reason: 'Only reserved document ids may start with underscore.'
  });
  
  var NOT_OPEN = new PouchError({
    status: 412,
    error: 'precondition_failed',
    reason: 'Database not open'
  });
  
  var UNKNOWN_ERROR = new PouchError({
    status: 500,
    error: 'unknown_error',
    reason: 'Database encountered an unknown error'
  });
  
  var BAD_ARG = new PouchError({
    status: 500,
    error: 'badarg',
    reason: 'Some query argument is invalid'
  });
  
  var INVALID_REQUEST = new PouchError({
    status: 400,
    error: 'invalid_request',
    reason: 'Request was invalid'
  });
  
  var QUERY_PARSE_ERROR = new PouchError({
    status: 400,
    error: 'query_parse_error',
    reason: 'Some query parameter is invalid'
  });
  
  var DOC_VALIDATION = new PouchError({
    status: 500,
    error: 'doc_validation',
    reason: 'Bad special document member'
  });
  
  var BAD_REQUEST = new PouchError({
    status: 400,
    error: 'bad_request',
    reason: 'Something wrong with the request'
  });
  
  var NOT_AN_OBJECT = new PouchError({
    status: 400,
    error: 'bad_request',
    reason: 'Document must be a JSON object'
  });
  
  var DB_MISSING = new PouchError({
    status: 404,
    error: 'not_found',
    reason: 'Database not found'
  });
  
  var IDB_ERROR = new PouchError({
    status: 500,
    error: 'indexed_db_went_bad',
    reason: 'unknown'
  });
  
  var WSQ_ERROR = new PouchError({
    status: 500,
    error: 'web_sql_went_bad',
    reason: 'unknown'
  });
  
  var LDB_ERROR = new PouchError({
    status: 500,
    error: 'levelDB_went_went_bad',
    reason: 'unknown'
  });
  
  var FORBIDDEN = new PouchError({
    status: 403,
    error: 'forbidden',
    reason: 'Forbidden by design doc validate_doc_update function'
  });
  
  var INVALID_REV = new PouchError({
    status: 400,
    error: 'bad_request',
    reason: 'Invalid rev format'
  });
  
  var FILE_EXISTS = new PouchError({
    status: 412,
    error: 'file_exists',
    reason: 'The database could not be created, the file already exists.'
  });
  
  var MISSING_STUB = new PouchError({
    status: 412,
    error: 'missing_stub'
  });
  
  var INVALID_URL = new PouchError({
    status: 413,
    error: 'invalid_url',
    reason: 'Provided URL is invalid'
  });
  
  function createError(error, reason) {
    function CustomPouchError(reason) {
      // inherit error properties from our parent error manually
      // so as to allow proper JSON parsing.
      /* jshint ignore:start */
      for (var p in error) {
        if (typeof error[p] !== 'function') {
          this[p] = error[p];
        }
      }
      /* jshint ignore:end */
      if (reason !== undefined) {
        this.reason = reason;
      }
    }
    CustomPouchError.prototype = PouchError.prototype;
    return new CustomPouchError(reason);
  }
  
  function generateErrorFromResponse(err) {
  
    if (typeof err !== 'object') {
      var data = err;
      err = UNKNOWN_ERROR;
      err.data = data;
    }
  
    if ('error' in err && err.error === 'conflict') {
      err.name = 'conflict';
      err.status = 409;
    }
  
    if (!('name' in err)) {
      err.name = err.error || 'unknown';
    }
  
    if (!('status' in err)) {
      err.status = 500;
    }
  
    if (!('message' in err)) {
      err.message = err.message || err.reason;
    }
  
    return err;
  }
  
  function tryFilter(filter, doc, req) {
    try {
      return !filter(doc, req);
    } catch (err) {
      var msg = 'Filter function threw: ' + err.toString();
      return createError(BAD_REQUEST, msg);
    }
  }
  
  function filterChange(opts) {
    var req = {};
    var hasFilter = opts.filter && typeof opts.filter === 'function';
    req.query = opts.query_params;
  
    return function filter(change) {
      if (!change.doc) {
        // CSG sends events on the changes feed that don't have documents,
        // this hack makes a whole lot of existing code robust.
        change.doc = {};
      }
  
      var filterReturn = hasFilter && tryFilter(opts.filter, change.doc, req);
  
      if (typeof filterReturn === 'object') {
        return filterReturn;
      }
  
      if (filterReturn) {
        return false;
      }
  
      if (!opts.include_docs) {
        delete change.doc;
      } else if (!opts.attachments) {
        for (var att in change.doc._attachments) {
          /* istanbul ignore else */
          if (change.doc._attachments.hasOwnProperty(att)) {
            change.doc._attachments[att].stub = true;
          }
        }
      }
      return true;
    };
  }
  
  function flatten(arrs) {
    var res = [];
    for (var i = 0, len = arrs.length; i < len; i++) {
      res = res.concat(arrs[i]);
    }
    return res;
  }
  
  // Determine id an ID is valid
  //   - invalid IDs begin with an underescore that does not begin '_design' or
  //     '_local'
  //   - any other string value is a valid id
  // Returns the specific error object for each case
  function invalidIdError(id) {
    var err;
    if (!id) {
      err = createError(MISSING_ID);
    } else if (typeof id !== 'string') {
      err = createError(INVALID_ID);
    } else if (/^_/.test(id) && !(/^_(design|local)/).test(id)) {
      err = createError(RESERVED_ID);
    }
    if (err) {
      throw err;
    }
  }
  
  function listenerCount(ee, type) {
    return 'listenerCount' in ee ? ee.listenerCount(type) :
                                   events.EventEmitter.listenerCount(ee, type);
  }
  
  function parseDesignDocFunctionName(s) {
    if (!s) {
      return null;
    }
    var parts = s.split('/');
    if (parts.length === 2) {
      return parts;
    }
    if (parts.length === 1) {
      return [s, s];
    }
    return null;
  }
  
  function normalizeDesignDocFunctionName(s) {
    var normalized = parseDesignDocFunctionName(s);
    return normalized ? normalized.join('/') : null;
  }
  
  // originally parseUri 1.2.2, now patched by us
  // (c) Steven Levithan <stevenlevithan.com>
  // MIT License
  var keys = ["source", "protocol", "authority", "userInfo", "user", "password",
      "host", "port", "relative", "path", "directory", "file", "query", "anchor"];
  var qName ="queryKey";
  var qParser = /(?:^|&)([^&=]*)=?([^&]*)/g;
  
  // use the "loose" parser
  /* jshint maxlen: false */
  var parser = /^(?:(?![^:@]+:[^:@\/]*@)([^:\/?#.]+):)?(?:\/\/)?((?:(([^:@]*)(?::([^:@]*))?)?@)?([^:\/?#]*)(?::(\d*))?)(((\/(?:[^?#](?![^?#\/]*\.[^?#\/.]+(?:[?#]|$)))*\/?)?([^?#\/]*))(?:\?([^#]*))?(?:#(.*))?)/;
  
  function parseUri(str) {
    var m = parser.exec(str);
    var uri = {};
    var i = 14;
  
    while (i--) {
      var key = keys[i];
      var value = m[i] || "";
      var encoded = ['user', 'password'].indexOf(key) !== -1;
      uri[key] = encoded ? decodeURIComponent(value) : value;
    }
  
    uri[qName] = {};
    uri[keys[12]].replace(qParser, function ($0, $1, $2) {
      if ($1) {
        uri[qName][$1] = $2;
      }
    });
  
    return uri;
  }
  
  // this is essentially the "update sugar" function from daleharvey/pouchdb#1388
  // the diffFun tells us what delta to apply to the doc.  it either returns
  // the doc, or false if it doesn't need to do an update after all
  function upsert(db, docId, diffFun) {
    return new PouchPromise(function (fulfill, reject) {
      db.get(docId, function (err, doc) {
        if (err) {
          /* istanbul ignore next */
          if (err.status !== 404) {
            return reject(err);
          }
          doc = {};
        }
  
        // the user might change the _rev, so save it for posterity
        var docRev = doc._rev;
        var newDoc = diffFun(doc);
  
        if (!newDoc) {
          // if the diffFun returns falsy, we short-circuit as
          // an optimization
          return fulfill({updated: false, rev: docRev});
        }
  
        // users aren't allowed to modify these values,
        // so reset them here
        newDoc._id = docId;
        newDoc._rev = docRev;
        fulfill(tryAndPut(db, newDoc, diffFun));
      });
    });
  }
  
  function tryAndPut(db, doc, diffFun) {
    return db.put(doc).then(function (res) {
      return {
        updated: true,
        rev: res.rev
      };
    }, function (err) {
      /* istanbul ignore next */
      if (err.status !== 409) {
        throw err;
      }
      return upsert(db, doc._id, diffFun);
    });
  }
  
  // BEGIN Math.uuid.js
  
  /*!
  Math.uuid.js (v1.4)
  http://www.broofa.com
  mailto:robert@broofa.com
  
  Copyright (c) 2010 Robert Kieffer
  Dual licensed under the MIT and GPL licenses.
  */
  
  /*
   * Generate a random uuid.
   *
   * USAGE: Math.uuid(length, radix)
   *   length - the desired number of characters
   *   radix  - the number of allowable values for each character.
   *
   * EXAMPLES:
   *   // No arguments  - returns RFC4122, version 4 ID
   *   >>> Math.uuid()
   *   "92329D39-6F5C-4520-ABFC-AAB64544E172"
   *
   *   // One argument - returns ID of the specified length
   *   >>> Math.uuid(15)     // 15 character ID (default base=62)
   *   "VcydxgltxrVZSTV"
   *
   *   // Two arguments - returns ID of the specified length, and radix. 
   *   // (Radix must be <= 62)
   *   >>> Math.uuid(8, 2)  // 8 character ID (base=2)
   *   "01001010"
   *   >>> Math.uuid(8, 10) // 8 character ID (base=10)
   *   "47473046"
   *   >>> Math.uuid(8, 16) // 8 character ID (base=16)
   *   "098F4D35"
   */
  var chars = (
    '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ' +
    'abcdefghijklmnopqrstuvwxyz'
  ).split('');
  function getValue(radix) {
    return 0 | Math.random() * radix;
  }
  function uuid(len, radix) {
    radix = radix || chars.length;
    var out = '';
    var i = -1;
  
    if (len) {
      // Compact form
      while (++i < len) {
        out += chars[getValue(radix)];
      }
      return out;
    }
      // rfc4122, version 4 form
      // Fill in random data.  At i==19 set the high bits of clock sequence as
      // per rfc4122, sec. 4.1.5
    while (++i < 36) {
      switch (i) {
        case 8:
        case 13:
        case 18:
        case 23:
          out += '-';
          break;
        case 19:
          out += chars[(getValue(16) & 0x3) | 0x8];
          break;
        default:
          out += chars[getValue(16)];
      }
    }
  
    return out;
  }
  
  // We fetch all leafs of the revision tree, and sort them based on tree length
  // and whether they were deleted, undeleted documents with the longest revision
  // tree (most edits) win
  // The final sort algorithm is slightly documented in a sidebar here:
  // http://guide.couchdb.org/draft/conflicts.html
  function winningRev(metadata) {
    var winningId;
    var winningPos;
    var winningDeleted;
    var toVisit = metadata.rev_tree.slice();
    var node;
    while ((node = toVisit.pop())) {
      var tree = node.ids;
      var branches = tree[2];
      var pos = node.pos;
      if (branches.length) { // non-leaf
        for (var i = 0, len = branches.length; i < len; i++) {
          toVisit.push({pos: pos + 1, ids: branches[i]});
        }
        continue;
      }
      var deleted = !!tree[1].deleted;
      var id = tree[0];
      // sort by deleted, then pos, then id
      if (!winningId || (winningDeleted !== deleted ? winningDeleted :
          winningPos !== pos ? winningPos < pos : winningId < id)) {
        winningId = id;
        winningPos = pos;
        winningDeleted = deleted;
      }
    }
  
    return winningPos + '-' + winningId;
  }
  
  // Pretty much all below can be combined into a higher order function to
  // traverse revisions
  // The return value from the callback will be passed as context to all
  // children of that node
  function traverseRevTree(revs, callback) {
    var toVisit = revs.slice();
  
    var node;
    while ((node = toVisit.pop())) {
      var pos = node.pos;
      var tree = node.ids;
      var branches = tree[2];
      var newCtx =
        callback(branches.length === 0, pos, tree[0], node.ctx, tree[1]);
      for (var i = 0, len = branches.length; i < len; i++) {
        toVisit.push({pos: pos + 1, ids: branches[i], ctx: newCtx});
      }
    }
  }
  
  function sortByPos(a, b) {
    return a.pos - b.pos;
  }
  
  function collectLeaves(revs) {
    var leaves = [];
    traverseRevTree(revs, function (isLeaf, pos, id, acc, opts) {
      if (isLeaf) {
        leaves.push({rev: pos + "-" + id, pos: pos, opts: opts});
      }
    });
    leaves.sort(sortByPos).reverse();
    for (var i = 0, len = leaves.length; i < len; i++) {
      delete leaves[i].pos;
    }
    return leaves;
  }
  
  // returns revs of all conflicts that is leaves such that
  // 1. are not deleted and
  // 2. are different than winning revision
  function collectConflicts(metadata) {
    var win = winningRev(metadata);
    var leaves = collectLeaves(metadata.rev_tree);
    var conflicts = [];
    for (var i = 0, len = leaves.length; i < len; i++) {
      var leaf = leaves[i];
      if (leaf.rev !== win && !leaf.opts.deleted) {
        conflicts.push(leaf.rev);
      }
    }
    return conflicts;
  }
  
  // compact a tree by marking its non-leafs as missing,
  // and return a list of revs to delete
  function compactTree(metadata) {
    var revs = [];
    traverseRevTree(metadata.rev_tree, function (isLeaf, pos,
                                                 revHash, ctx, opts) {
      if (opts.status === 'available' && !isLeaf) {
        revs.push(pos + '-' + revHash);
        opts.status = 'missing';
      }
    });
    return revs;
  }
  
  // build up a list of all the paths to the leafs in this revision tree
  function rootToLeaf(revs) {
    var paths = [];
    var toVisit = revs.slice();
    var node;
    while ((node = toVisit.pop())) {
      var pos = node.pos;
      var tree = node.ids;
      var id = tree[0];
      var opts = tree[1];
      var branches = tree[2];
      var isLeaf = branches.length === 0;
  
      var history = node.history ? node.history.slice() : [];
      history.push({id: id, opts: opts});
      if (isLeaf) {
        paths.push({pos: (pos + 1 - history.length), ids: history});
      }
      for (var i = 0, len = branches.length; i < len; i++) {
        toVisit.push({pos: pos + 1, ids: branches[i], history: history});
      }
    }
    return paths.reverse();
  }
  
  // for a better overview of what this is doing, read:
  // https://github.com/apache/couchdb-couch/blob/master/src/couch_key_tree.erl
  //
  // But for a quick intro, CouchDB uses a revision tree to store a documents
  // history, A -> B -> C, when a document has conflicts, that is a branch in the
  // tree, A -> (B1 | B2 -> C), We store these as a nested array in the format
  //
  // KeyTree = [Path ... ]
  // Path = {pos: position_from_root, ids: Tree}
  // Tree = [Key, Opts, [Tree, ...]], in particular single node: [Key, []]
  
  function sortByPos$1(a, b) {
    return a.pos - b.pos;
  }
  
  // classic binary search
  function binarySearch(arr, item, comparator) {
    var low = 0;
    var high = arr.length;
    var mid;
    while (low < high) {
      mid = (low + high) >>> 1;
      if (comparator(arr[mid], item) < 0) {
        low = mid + 1;
      } else {
        high = mid;
      }
    }
    return low;
  }
  
  // assuming the arr is sorted, insert the item in the proper place
  function insertSorted(arr, item, comparator) {
    var idx = binarySearch(arr, item, comparator);
    arr.splice(idx, 0, item);
  }
  
  // Turn a path as a flat array into a tree with a single branch.
  // If any should be stemmed from the beginning of the array, that's passed
  // in as the second argument
  function pathToTree(path, numStemmed) {
    var root;
    var leaf;
    for (var i = numStemmed, len = path.length; i < len; i++) {
      var node = path[i];
      var currentLeaf = [node.id, node.opts, []];
      if (leaf) {
        leaf[2].push(currentLeaf);
        leaf = currentLeaf;
      } else {
        root = leaf = currentLeaf;
      }
    }
    return root;
  }
  
  // compare the IDs of two trees
  function compareTree(a, b) {
    return a[0] < b[0] ? -1 : 1;
  }
  
  // Merge two trees together
  // The roots of tree1 and tree2 must be the same revision
  function mergeTree(in_tree1, in_tree2) {
    var queue = [{tree1: in_tree1, tree2: in_tree2}];
    var conflicts = false;
    while (queue.length > 0) {
      var item = queue.pop();
      var tree1 = item.tree1;
      var tree2 = item.tree2;
  
      if (tree1[1].status || tree2[1].status) {
        tree1[1].status =
          (tree1[1].status ===  'available' ||
          tree2[1].status === 'available') ? 'available' : 'missing';
      }
  
      for (var i = 0; i < tree2[2].length; i++) {
        if (!tree1[2][0]) {
          conflicts = 'new_leaf';
          tree1[2][0] = tree2[2][i];
          continue;
        }
  
        var merged = false;
        for (var j = 0; j < tree1[2].length; j++) {
          if (tree1[2][j][0] === tree2[2][i][0]) {
            queue.push({tree1: tree1[2][j], tree2: tree2[2][i]});
            merged = true;
          }
        }
        if (!merged) {
          conflicts = 'new_branch';
          insertSorted(tree1[2], tree2[2][i], compareTree);
        }
      }
    }
    return {conflicts: conflicts, tree: in_tree1};
  }
  
  function doMerge(tree, path, dontExpand) {
    var restree = [];
    var conflicts = false;
    var merged = false;
    var res;
  
    if (!tree.length) {
      return {tree: [path], conflicts: 'new_leaf'};
    }
  
    for (var i = 0, len = tree.length; i < len; i++) {
      var branch = tree[i];
      if (branch.pos === path.pos && branch.ids[0] === path.ids[0]) {
        // Paths start at the same position and have the same root, so they need
        // merged
        res = mergeTree(branch.ids, path.ids);
        restree.push({pos: branch.pos, ids: res.tree});
        conflicts = conflicts || res.conflicts;
        merged = true;
      } else if (dontExpand !== true) {
        // The paths start at a different position, take the earliest path and
        // traverse up until it as at the same point from root as the path we
        // want to merge.  If the keys match we return the longer path with the
        // other merged After stemming we dont want to expand the trees
  
        var t1 = branch.pos < path.pos ? branch : path;
        var t2 = branch.pos < path.pos ? path : branch;
        var diff = t2.pos - t1.pos;
  
        var candidateParents = [];
  
        var trees = [];
        trees.push({ids: t1.ids, diff: diff, parent: null, parentIdx: null});
        while (trees.length > 0) {
          var item = trees.pop();
          if (item.diff === 0) {
            if (item.ids[0] === t2.ids[0]) {
              candidateParents.push(item);
            }
            continue;
          }
          var elements = item.ids[2];
          for (var j = 0, elementsLen = elements.length; j < elementsLen; j++) {
            trees.push({
              ids: elements[j],
              diff: item.diff - 1,
              parent: item.ids,
              parentIdx: j
            });
          }
        }
  
        var el = candidateParents[0];
  
        if (!el) {
          restree.push(branch);
        } else {
          res = mergeTree(el.ids, t2.ids);
          el.parent[2][el.parentIdx] = res.tree;
          restree.push({pos: t1.pos, ids: t1.ids});
          conflicts = conflicts || res.conflicts;
          merged = true;
        }
      } else {
        restree.push(branch);
      }
    }
  
    // We didnt find
    if (!merged) {
      restree.push(path);
    }
  
    restree.sort(sortByPos$1);
  
    return {
      tree: restree,
      conflicts: conflicts || 'internal_node'
    };
  }
  
  // To ensure we dont grow the revision tree infinitely, we stem old revisions
  function stem(tree, depth) {
    // First we break out the tree into a complete list of root to leaf paths
    var paths = rootToLeaf(tree);
    var maybeStem = {};
  
    var result;
    for (var i = 0, len = paths.length; i < len; i++) {
      // Then for each path, we cut off the start of the path based on the
      // `depth` to stem to, and generate a new set of flat trees
      var path = paths[i];
      var stemmed = path.ids;
      var numStemmed = Math.max(0, stemmed.length - depth);
      var stemmedNode = {
        pos: path.pos + numStemmed,
        ids: pathToTree(stemmed, numStemmed)
      };
  
      for (var s = 0; s < numStemmed; s++) {
        var rev = (path.pos + s) + '-' + stemmed[s].id;
        maybeStem[rev] = true;
      }
  
      // Then we remerge all those flat trees together, ensuring that we dont
      // connect trees that would go beyond the depth limit
      if (result) {
        result = doMerge(result, stemmedNode, true).tree;
      } else {
        result = [stemmedNode];
      }
    }
  
    traverseRevTree(result, function (isLeaf, pos, revHash) {
      // some revisions may have been removed in a branch but not in another
      delete maybeStem[pos + '-' + revHash];
    });
  
    return {
      tree: result,
      revs: Object.keys(maybeStem)
    };
  }
  
  function merge(tree, path, depth) {
    var newTree = doMerge(tree, path);
    var stemmed = stem(newTree.tree, depth);
    return {
      tree: stemmed.tree,
      stemmedRevs: stemmed.revs,
      conflicts: newTree.conflicts
    };
  }
  
  // return true if a rev exists in the rev tree, false otherwise
  function revExists(revs, rev) {
    var toVisit = revs.slice();
    var splitRev = rev.split('-');
    var targetPos = parseInt(splitRev[0], 10);
    var targetId = splitRev[1];
  
    var node;
    while ((node = toVisit.pop())) {
      if (node.pos === targetPos && node.ids[0] === targetId) {
        return true;
      }
      var branches = node.ids[2];
      for (var i = 0, len = branches.length; i < len; i++) {
        toVisit.push({pos: node.pos + 1, ids: branches[i]});
      }
    }
    return false;
  }
  
  function getTrees(node) {
    return node.ids;
  }
  
  // check if a specific revision of a doc has been deleted
  //  - metadata: the metadata object from the doc store
  //  - rev: (optional) the revision to check. defaults to winning revision
  function isDeleted(metadata, rev) {
    if (!rev) {
      rev = winningRev(metadata);
    }
    var id = rev.substring(rev.indexOf('-') + 1);
    var toVisit = metadata.rev_tree.map(getTrees);
  
    var tree;
    while ((tree = toVisit.pop())) {
      if (tree[0] === id) {
        return !!tree[1].deleted;
      }
      toVisit = toVisit.concat(tree[2]);
    }
  }
  
  function isLocalId(id) {
    return (/^_local/).test(id);
  }
  
  function evalFilter(input) {
    return scopedEval('"use strict";\nreturn ' + input + ';', {});
  }
  
  function evalView(input) {
    var code = [
      'return function(doc) {',
      '  "use strict";',
      '  var emitted = false;',
      '  var emit = function (a, b) {',
      '    emitted = true;',
      '  };',
      '  var view = ' + input + ';',
      '  view(doc);',
      '  if (emitted) {',
      '    return true;',
      '  }',
      '};'
    ].join('\n');
  
    return scopedEval(code, {});
  }
  
  inherits(Changes, events.EventEmitter);
  
  function tryCatchInChangeListener(self, change) {
    // isolate try/catches to avoid V8 deoptimizations
    try {
      self.emit('change', change);
    } catch (e) {
      guardedConsole('error', 'Error in .on("change", function):', e);
    }
  }
  
  function Changes(db, opts, callback) {
    events.EventEmitter.call(this);
    var self = this;
    this.db = db;
    opts = opts ? clone(opts) : {};
    var complete = opts.complete = once(function (err, resp) {
      if (err) {
        if (listenerCount(self, 'error') > 0) {
          self.emit('error', err);
        }
      } else {
        self.emit('complete', resp);
      }
      self.removeAllListeners();
      db.removeListener('destroyed', onDestroy);
    });
    if (callback) {
      self.on('complete', function (resp) {
        callback(null, resp);
      });
      self.on('error', callback);
    }
    function onDestroy() {
      self.cancel();
    }
    db.once('destroyed', onDestroy);
  
    opts.onChange = function (change) {
      /* istanbul ignore if */
      if (opts.isCancelled) {
        return;
      }
      tryCatchInChangeListener(self, change);
    };
  
    var promise = new PouchPromise(function (fulfill, reject) {
      opts.complete = function (err, res) {
        if (err) {
          reject(err);
        } else {
          fulfill(res);
        }
      };
    });
    self.once('cancel', function () {
      db.removeListener('destroyed', onDestroy);
      opts.complete(null, {status: 'cancelled'});
    });
    this.then = promise.then.bind(promise);
    this['catch'] = promise['catch'].bind(promise);
    this.then(function (result) {
      complete(null, result);
    }, complete);
  
  
  
    if (!db.taskqueue.isReady) {
      db.taskqueue.addTask(function (failed) {
        if (failed) {
          opts.complete(failed);
        } else if (self.isCancelled) {
          self.emit('cancel');
        } else {
          self.doChanges(opts);
        }
      });
    } else {
      self.doChanges(opts);
    }
  }
  Changes.prototype.cancel = function () {
    this.isCancelled = true;
    if (this.db.taskqueue.isReady) {
      this.emit('cancel');
    }
  };
  function processChange(doc, metadata, opts) {
    var changeList = [{rev: doc._rev}];
    if (opts.style === 'all_docs') {
      changeList = collectLeaves(metadata.rev_tree)
      .map(function (x) { return {rev: x.rev}; });
    }
    var change = {
      id: metadata.id,
      changes: changeList,
      doc: doc
    };
  
    if (isDeleted(metadata, doc._rev)) {
      change.deleted = true;
    }
    if (opts.conflicts) {
      change.doc._conflicts = collectConflicts(metadata);
      if (!change.doc._conflicts.length) {
        delete change.doc._conflicts;
      }
    }
    return change;
  }
  
  Changes.prototype.doChanges = function (opts) {
    var self = this;
    var callback = opts.complete;
  
    opts = clone(opts);
    if ('live' in opts && !('continuous' in opts)) {
      opts.continuous = opts.live;
    }
    opts.processChange = processChange;
  
    if (opts.since === 'latest') {
      opts.since = 'now';
    }
    if (!opts.since) {
      opts.since = 0;
    }
    if (opts.since === 'now') {
      this.db.info().then(function (info) {
        /* istanbul ignore if */
        if (self.isCancelled) {
          callback(null, {status: 'cancelled'});
          return;
        }
        opts.since = info.update_seq;
        self.doChanges(opts);
      }, callback);
      return;
    }
  
  
    if (opts.view && !opts.filter) {
      opts.filter = '_view';
    }
  
    if (opts.filter && typeof opts.filter === 'string') {
      if (opts.filter === '_view') {
        opts.view = normalizeDesignDocFunctionName(opts.view);
      } else {
        opts.filter = normalizeDesignDocFunctionName(opts.filter);
      }
  
      if (this.db.type() !== 'http' && !opts.doc_ids) {
        return this.filterChanges(opts);
      }
    }
  
    if (!('descending' in opts)) {
      opts.descending = false;
    }
  
    // 0 and 1 should return 1 document
    opts.limit = opts.limit === 0 ? 1 : opts.limit;
    opts.complete = callback;
    var newPromise = this.db._changes(opts);
    /* istanbul ignore else */
    if (newPromise && typeof newPromise.cancel === 'function') {
      var cancel = self.cancel;
      self.cancel = getArguments(function (args) {
        newPromise.cancel();
        cancel.apply(this, args);
      });
    }
  };
  
  Changes.prototype.filterChanges = function (opts) {
    var self = this;
    var callback = opts.complete;
    if (opts.filter === '_view') {
      if (!opts.view || typeof opts.view !== 'string') {
        var err = createError(BAD_REQUEST,
          '`view` filter parameter not found or invalid.');
        return callback(err);
      }
      // fetch a view from a design doc, make it behave like a filter
      var viewName = parseDesignDocFunctionName(opts.view);
      this.db.get('_design/' + viewName[0], function (err, ddoc) {
        /* istanbul ignore if */
        if (self.isCancelled) {
          return callback(null, {status: 'cancelled'});
        }
        /* istanbul ignore next */
        if (err) {
          return callback(generateErrorFromResponse(err));
        }
        var mapFun = ddoc && ddoc.views && ddoc.views[viewName[1]] &&
          ddoc.views[viewName[1]].map;
        if (!mapFun) {
          return callback(createError(MISSING_DOC,
            (ddoc.views ? 'missing json key: ' + viewName[1] :
              'missing json key: views')));
        }
        opts.filter = evalView(mapFun);
        self.doChanges(opts);
      });
    } else {
      // fetch a filter from a design doc
      var filterName = parseDesignDocFunctionName(opts.filter);
      if (!filterName) {
        return self.doChanges(opts);
      }
      this.db.get('_design/' + filterName[0], function (err, ddoc) {
        /* istanbul ignore if */
        if (self.isCancelled) {
          return callback(null, {status: 'cancelled'});
        }
        /* istanbul ignore next */
        if (err) {
          return callback(generateErrorFromResponse(err));
        }
        var filterFun = ddoc && ddoc.filters && ddoc.filters[filterName[1]];
        if (!filterFun) {
          return callback(createError(MISSING_DOC,
            ((ddoc && ddoc.filters) ? 'missing json key: ' + filterName[1]
              : 'missing json key: filters')));
        }
        opts.filter = evalFilter(filterFun);
        self.doChanges(opts);
      });
    }
  };
  
  /*
   * A generic pouch adapter
   */
  
  function compare(left, right) {
    return left < right ? -1 : left > right ? 1 : 0;
  }
  
  // returns first element of arr satisfying callback predicate
  function arrayFirst(arr, callback) {
    for (var i = 0; i < arr.length; i++) {
      if (callback(arr[i], i) === true) {
        return arr[i];
      }
    }
  }
  
  // Wrapper for functions that call the bulkdocs api with a single doc,
  // if the first result is an error, return an error
  function yankError(callback) {
    return function (err, results) {
      if (err || (results[0] && results[0].error)) {
        callback(err || results[0]);
      } else {
        callback(null, results.length ? results[0]  : results);
      }
    };
  }
  
  // clean docs given to us by the user
  function cleanDocs(docs) {
    for (var i = 0; i < docs.length; i++) {
      var doc = docs[i];
      if (doc._deleted) {
        delete doc._attachments; // ignore atts for deleted docs
      } else if (doc._attachments) {
        // filter out extraneous keys from _attachments
        var atts = Object.keys(doc._attachments);
        for (var j = 0; j < atts.length; j++) {
          var att = atts[j];
          doc._attachments[att] = pick(doc._attachments[att],
            ['data', 'digest', 'content_type', 'length', 'revpos', 'stub']);
        }
      }
    }
  }
  
  // compare two docs, first by _id then by _rev
  function compareByIdThenRev(a, b) {
    var idCompare = compare(a._id, b._id);
    if (idCompare !== 0) {
      return idCompare;
    }
    var aStart = a._revisions ? a._revisions.start : 0;
    var bStart = b._revisions ? b._revisions.start : 0;
    return compare(aStart, bStart);
  }
  
  // for every node in a revision tree computes its distance from the closest
  // leaf
  function computeHeight(revs) {
    var height = {};
    var edges = [];
    traverseRevTree(revs, function (isLeaf, pos, id, prnt) {
      var rev = pos + "-" + id;
      if (isLeaf) {
        height[rev] = 0;
      }
      if (prnt !== undefined) {
        edges.push({from: prnt, to: rev});
      }
      return rev;
    });
  
    edges.reverse();
    edges.forEach(function (edge) {
      if (height[edge.from] === undefined) {
        height[edge.from] = 1 + height[edge.to];
      } else {
        height[edge.from] = Math.min(height[edge.from], 1 + height[edge.to]);
      }
    });
    return height;
  }
  
  function allDocsKeysQuery(api, opts, callback) {
    var keys =  ('limit' in opts) ?
        opts.keys.slice(opts.skip, opts.limit + opts.skip) :
        (opts.skip > 0) ? opts.keys.slice(opts.skip) : opts.keys;
    if (opts.descending) {
      keys.reverse();
    }
    if (!keys.length) {
      return api._allDocs({limit: 0}, callback);
    }
    var finalResults = {
      offset: opts.skip
    };
    return PouchPromise.all(keys.map(function (key) {
      var subOpts = jsExtend.extend({key: key, deleted: 'ok'}, opts);
      ['limit', 'skip', 'keys'].forEach(function (optKey) {
        delete subOpts[optKey];
      });
      return new PouchPromise(function (resolve, reject) {
        api._allDocs(subOpts, function (err, res) {
          /* istanbul ignore if */
          if (err) {
            return reject(err);
          }
          finalResults.total_rows = res.total_rows;
          resolve(res.rows[0] || {key: key, error: 'not_found'});
        });
      });
    })).then(function (results) {
      finalResults.rows = results;
      return finalResults;
    });
  }
  
  // all compaction is done in a queue, to avoid attaching
  // too many listeners at once
  function doNextCompaction(self) {
    var task = self._compactionQueue[0];
    var opts = task.opts;
    var callback = task.callback;
    self.get('_local/compaction')["catch"](function () {
      return false;
    }).then(function (doc) {
      if (doc && doc.last_seq) {
        opts.last_seq = doc.last_seq;
      }
      self._compact(opts, function (err, res) {
        /* istanbul ignore if */
        if (err) {
          callback(err);
        } else {
          callback(null, res);
        }
        process.nextTick(function () {
          self._compactionQueue.shift();
          if (self._compactionQueue.length) {
            doNextCompaction(self);
          }
        });
      });
    });
  }
  
  function attachmentNameError(name) {
    if (name.charAt(0) === '_') {
      return name + 'is not a valid attachment name, attachment ' +
        'names cannot start with \'_\'';
    }
    return false;
  }
  
  inherits(AbstractPouchDB, events.EventEmitter);
  
  function AbstractPouchDB() {
    events.EventEmitter.call(this);
  }
  
  AbstractPouchDB.prototype.post =
    adapterFun('post', function (doc, opts, callback) {
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
    if (typeof doc !== 'object' || Array.isArray(doc)) {
      return callback(createError(NOT_AN_OBJECT));
    }
    this.bulkDocs({docs: [doc]}, opts, yankError(callback));
  });
  
  AbstractPouchDB.prototype.put = adapterFun('put', function (doc, opts, cb) {
    if (typeof opts === 'function') {
      cb = opts;
      opts = {};
    }
    if (typeof doc !== 'object' || Array.isArray(doc)) {
      return cb(createError(NOT_AN_OBJECT));
    }
    invalidIdError(doc._id);
    if (isLocalId(doc._id) && typeof this._putLocal === 'function') {
      if (doc._deleted) {
        return this._removeLocal(doc, cb);
      } else {
        return this._putLocal(doc, cb);
      }
    }
    if (typeof this._put === 'function' && opts.new_edits !== false) {
      this._put(doc, opts, cb);
    } else {
      this.bulkDocs({docs: [doc]}, opts, yankError(cb));
    }
  });
  
  AbstractPouchDB.prototype.putAttachment =
    adapterFun('putAttachment', function (docId, attachmentId, rev,
                                                blob, type) {
    var api = this;
    if (typeof type === 'function') {
      type = blob;
      blob = rev;
      rev = null;
    }
    // Lets fix in https://github.com/pouchdb/pouchdb/issues/3267
    /* istanbul ignore if */
    if (typeof type === 'undefined') {
      type = blob;
      blob = rev;
      rev = null;
    }
  
    function createAttachment(doc) {
      var prevrevpos = '_rev' in doc ? parseInt(doc._rev, 10) : 0;
      doc._attachments = doc._attachments || {};
      doc._attachments[attachmentId] = {
        content_type: type,
        data: blob,
        revpos: ++prevrevpos
      };
      return api.put(doc);
    }
  
    return api.get(docId).then(function (doc) {
      if (doc._rev !== rev) {
        throw createError(REV_CONFLICT);
      }
  
      return createAttachment(doc);
    }, function (err) {
       // create new doc
      /* istanbul ignore else */
      if (err.reason === MISSING_DOC.message) {
        return createAttachment({_id: docId});
      } else {
        throw err;
      }
    });
  });
  
  AbstractPouchDB.prototype.removeAttachment =
    adapterFun('removeAttachment', function (docId, attachmentId, rev,
                                                   callback) {
    var self = this;
    self.get(docId, function (err, obj) {
      /* istanbul ignore if */
      if (err) {
        callback(err);
        return;
      }
      if (obj._rev !== rev) {
        callback(createError(REV_CONFLICT));
        return;
      }
      /* istanbul ignore if */
      if (!obj._attachments) {
        return callback();
      }
      delete obj._attachments[attachmentId];
      if (Object.keys(obj._attachments).length === 0) {
        delete obj._attachments;
      }
      self.put(obj, callback);
    });
  });
  
  AbstractPouchDB.prototype.remove =
    adapterFun('remove', function (docOrId, optsOrRev, opts, callback) {
    var doc;
    if (typeof optsOrRev === 'string') {
      // id, rev, opts, callback style
      doc = {
        _id: docOrId,
        _rev: optsOrRev
      };
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
    } else {
      // doc, opts, callback style
      doc = docOrId;
      if (typeof optsOrRev === 'function') {
        callback = optsOrRev;
        opts = {};
      } else {
        callback = opts;
        opts = optsOrRev;
      }
    }
    opts = opts || {};
    opts.was_delete = true;
    var newDoc = {_id: doc._id, _rev: (doc._rev || opts.rev)};
    newDoc._deleted = true;
    if (isLocalId(newDoc._id) && typeof this._removeLocal === 'function') {
      return this._removeLocal(doc, callback);
    }
    this.bulkDocs({docs: [newDoc]}, opts, yankError(callback));
  });
  
  AbstractPouchDB.prototype.revsDiff =
    adapterFun('revsDiff', function (req, opts, callback) {
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
    var ids = Object.keys(req);
  
    if (!ids.length) {
      return callback(null, {});
    }
  
    var count = 0;
    var missing = new _Map();
  
    function addToMissing(id, revId) {
      if (!missing.has(id)) {
        missing.set(id, {missing: []});
      }
      missing.get(id).missing.push(revId);
    }
  
    function processDoc(id, rev_tree) {
      // Is this fast enough? Maybe we should switch to a set simulated by a map
      var missingForId = req[id].slice(0);
      traverseRevTree(rev_tree, function (isLeaf, pos, revHash, ctx,
        opts) {
          var rev = pos + '-' + revHash;
          var idx = missingForId.indexOf(rev);
          if (idx === -1) {
            return;
          }
  
          missingForId.splice(idx, 1);
          /* istanbul ignore if */
          if (opts.status !== 'available') {
            addToMissing(id, rev);
          }
        });
  
      // Traversing the tree is synchronous, so now `missingForId` contains
      // revisions that were not found in the tree
      missingForId.forEach(function (rev) {
        addToMissing(id, rev);
      });
    }
  
    ids.map(function (id) {
      this._getRevisionTree(id, function (err, rev_tree) {
        if (err && err.status === 404 && err.message === 'missing') {
          missing.set(id, {missing: req[id]});
        } else if (err) {
          /* istanbul ignore next */
          return callback(err);
        } else {
          processDoc(id, rev_tree);
        }
  
        if (++count === ids.length) {
          // convert LazyMap to object
          var missingObj = {};
          missing.forEach(function (value, key) {
            missingObj[key] = value;
          });
          return callback(null, missingObj);
        }
      });
    }, this);
  });
  
  // _bulk_get API for faster replication, as described in
  // https://github.com/apache/couchdb-chttpd/pull/33
  // At the "abstract" level, it will just run multiple get()s in
  // parallel, because this isn't much of a performance cost
  // for local databases (except the cost of multiple transactions, which is
  // small). The http adapter overrides this in order
  // to do a more efficient single HTTP request.
  AbstractPouchDB.prototype.bulkGet =
    adapterFun('bulkGet', function (opts, callback) {
    bulkGet(this, opts, callback);
  });
  
  // compact one document and fire callback
  // by compacting we mean removing all revisions which
  // are further from the leaf in revision tree than max_height
  AbstractPouchDB.prototype.compactDocument =
    adapterFun('compactDocument', function (docId, maxHeight, callback) {
    var self = this;
    this._getRevisionTree(docId, function (err, revTree) {
      /* istanbul ignore if */
      if (err) {
        return callback(err);
      }
      var height = computeHeight(revTree);
      var candidates = [];
      var revs = [];
      Object.keys(height).forEach(function (rev) {
        if (height[rev] > maxHeight) {
          candidates.push(rev);
        }
      });
  
      traverseRevTree(revTree, function (isLeaf, pos, revHash, ctx, opts) {
        var rev = pos + '-' + revHash;
        if (opts.status === 'available' && candidates.indexOf(rev) !== -1) {
          revs.push(rev);
        }
      });
      self._doCompaction(docId, revs, callback);
    });
  });
  
  // compact the whole database using single document
  // compaction
  AbstractPouchDB.prototype.compact =
    adapterFun('compact', function (opts, callback) {
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
  
    var self = this;
    opts = opts || {};
  
    self._compactionQueue = self._compactionQueue || [];
    self._compactionQueue.push({opts: opts, callback: callback});
    if (self._compactionQueue.length === 1) {
      doNextCompaction(self);
    }
  });
  AbstractPouchDB.prototype._compact = function (opts, callback) {
    var self = this;
    var changesOpts = {
      return_docs: false,
      last_seq: opts.last_seq || 0
    };
    var promises = [];
  
    function onChange(row) {
      promises.push(self.compactDocument(row.id, 0));
    }
    function onComplete(resp) {
      var lastSeq = resp.last_seq;
      PouchPromise.all(promises).then(function () {
        return upsert(self, '_local/compaction', function deltaFunc(doc) {
          if (!doc.last_seq || doc.last_seq < lastSeq) {
            doc.last_seq = lastSeq;
            return doc;
          }
          return false; // somebody else got here first, don't update
        });
      }).then(function () {
        callback(null, {ok: true});
      })["catch"](callback);
    }
    self.changes(changesOpts)
      .on('change', onChange)
      .on('complete', onComplete)
      .on('error', callback);
  };
  
  /* Begin api wrappers. Specific functionality to storage belongs in the
     _[method] */
  AbstractPouchDB.prototype.get = adapterFun('get', function (id, opts, cb) {
    if (typeof opts === 'function') {
      cb = opts;
      opts = {};
    }
    if (typeof id !== 'string') {
      return cb(createError(INVALID_ID));
    }
    if (isLocalId(id) && typeof this._getLocal === 'function') {
      return this._getLocal(id, cb);
    }
    var leaves = [], self = this;
  
    function finishOpenRevs() {
      var result = [];
      var count = leaves.length;
      /* istanbul ignore if */
      if (!count) {
        return cb(null, result);
      }
      // order with open_revs is unspecified
      leaves.forEach(function (leaf) {
        self.get(id, {
          rev: leaf,
          revs: opts.revs,
          attachments: opts.attachments
        }, function (err, doc) {
          if (!err) {
            result.push({ok: doc});
          } else {
            result.push({missing: leaf});
          }
          count--;
          if (!count) {
            cb(null, result);
          }
        });
      });
    }
  
    if (opts.open_revs) {
      if (opts.open_revs === "all") {
        this._getRevisionTree(id, function (err, rev_tree) {
          if (err) {
            return cb(err);
          }
          leaves = collectLeaves(rev_tree).map(function (leaf) {
            return leaf.rev;
          });
          finishOpenRevs();
        });
      } else {
        if (Array.isArray(opts.open_revs)) {
          leaves = opts.open_revs;
          for (var i = 0; i < leaves.length; i++) {
            var l = leaves[i];
            // looks like it's the only thing couchdb checks
            if (!(typeof (l) === "string" && /^\d+-/.test(l))) {
              return cb(createError(INVALID_REV));
            }
          }
          finishOpenRevs();
        } else {
          return cb(createError(UNKNOWN_ERROR, 'function_clause'));
        }
      }
      return; // open_revs does not like other options
    }
  
    return this._get(id, opts, function (err, result) {
      if (err) {
        return cb(err);
      }
  
      var doc = result.doc;
      var metadata = result.metadata;
      var ctx = result.ctx;
  
      if (opts.conflicts) {
        var conflicts = collectConflicts(metadata);
        if (conflicts.length) {
          doc._conflicts = conflicts;
        }
      }
  
      if (isDeleted(metadata, doc._rev)) {
        doc._deleted = true;
      }
  
      if (opts.revs || opts.revs_info) {
        var paths = rootToLeaf(metadata.rev_tree);
        var path = arrayFirst(paths, function (arr) {
          return arr.ids.map(function (x) { return x.id; })
            .indexOf(doc._rev.split('-')[1]) !== -1;
        });
  
        var indexOfRev = path.ids.map(function (x) {return x.id; })
          .indexOf(doc._rev.split('-')[1]) + 1;
        var howMany = path.ids.length - indexOfRev;
        path.ids.splice(indexOfRev, howMany);
        path.ids.reverse();
  
        if (opts.revs) {
          doc._revisions = {
            start: (path.pos + path.ids.length) - 1,
            ids: path.ids.map(function (rev) {
              return rev.id;
            })
          };
        }
        if (opts.revs_info) {
          var pos =  path.pos + path.ids.length;
          doc._revs_info = path.ids.map(function (rev) {
            pos--;
            return {
              rev: pos + '-' + rev.id,
              status: rev.opts.status
            };
          });
        }
      }
  
      if (opts.attachments && doc._attachments) {
        var attachments = doc._attachments;
        var count = Object.keys(attachments).length;
        if (count === 0) {
          return cb(null, doc);
        }
        Object.keys(attachments).forEach(function (key) {
          this._getAttachment(doc._id, key, attachments[key], {
            // Previously the revision handling was done in adapter.js
            // getAttachment, however since idb-next doesnt we need to
            // pass the rev through
            rev: doc._rev,
            binary: opts.binary,
            ctx: ctx
          }, function (err, data) {
            var att = doc._attachments[key];
            att.data = data;
            delete att.stub;
            delete att.length;
            if (!--count) {
              cb(null, doc);
            }
          });
        }, self);
      } else {
        if (doc._attachments) {
          for (var key in doc._attachments) {
            /* istanbul ignore else */
            if (doc._attachments.hasOwnProperty(key)) {
              doc._attachments[key].stub = true;
            }
          }
        }
        cb(null, doc);
      }
    });
  });
  
  // TODO: I dont like this, it forces an extra read for every
  // attachment read and enforces a confusing api between
  // adapter.js and the adapter implementation
  AbstractPouchDB.prototype.getAttachment =
    adapterFun('getAttachment', function (docId, attachmentId, opts, callback) {
    var self = this;
    if (opts instanceof Function) {
      callback = opts;
      opts = {};
    }
    this._get(docId, opts, function (err, res) {
      if (err) {
        return callback(err);
      }
      if (res.doc._attachments && res.doc._attachments[attachmentId]) {
        opts.ctx = res.ctx;
        opts.binary = true;
        self._getAttachment(docId, attachmentId,
                            res.doc._attachments[attachmentId], opts, callback);
      } else {
        return callback(createError(MISSING_DOC));
      }
    });
  });
  
  AbstractPouchDB.prototype.allDocs =
    adapterFun('allDocs', function (opts, callback) {
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
    opts.skip = typeof opts.skip !== 'undefined' ? opts.skip : 0;
    if (opts.start_key) {
      opts.startkey = opts.start_key;
    }
    if (opts.end_key) {
      opts.endkey = opts.end_key;
    }
    if ('keys' in opts) {
      if (!Array.isArray(opts.keys)) {
        return callback(new TypeError('options.keys must be an array'));
      }
      var incompatibleOpt =
        ['startkey', 'endkey', 'key'].filter(function (incompatibleOpt) {
        return incompatibleOpt in opts;
      })[0];
      if (incompatibleOpt) {
        callback(createError(QUERY_PARSE_ERROR,
          'Query parameter `' + incompatibleOpt +
          '` is not compatible with multi-get'
        ));
        return;
      }
      if (this.type() !== 'http') {
        return allDocsKeysQuery(this, opts, callback);
      }
    }
  
    return this._allDocs(opts, callback);
  });
  
  AbstractPouchDB.prototype.changes = function (opts, callback) {
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
    return new Changes(this, opts, callback);
  };
  
  AbstractPouchDB.prototype.close = adapterFun('close', function (callback) {
    this._closed = true;
    return this._close(callback);
  });
  
  AbstractPouchDB.prototype.info = adapterFun('info', function (callback) {
    var self = this;
    this._info(function (err, info) {
      if (err) {
        return callback(err);
      }
      // assume we know better than the adapter, unless it informs us
      info.db_name = info.db_name || self.name;
      info.auto_compaction = !!(self.auto_compaction && self.type() !== 'http');
      info.adapter = self.type();
      callback(null, info);
    });
  });
  
  AbstractPouchDB.prototype.id = adapterFun('id', function (callback) {
    return this._id(callback);
  });
  
  /* istanbul ignore next */
  AbstractPouchDB.prototype.type = function () {
    return (typeof this._type === 'function') ? this._type() : this.adapter;
  };
  
  AbstractPouchDB.prototype.bulkDocs =
    adapterFun('bulkDocs', function (req, opts, callback) {
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
  
    opts = opts || {};
  
    if (Array.isArray(req)) {
      req = {
        docs: req
      };
    }
  
    if (!req || !req.docs || !Array.isArray(req.docs)) {
      return callback(createError(MISSING_BULK_DOCS));
    }
  
    for (var i = 0; i < req.docs.length; ++i) {
      if (typeof req.docs[i] !== 'object' || Array.isArray(req.docs[i])) {
        return callback(createError(NOT_AN_OBJECT));
      }
    }
  
    var attachmentError;
    req.docs.forEach(function (doc) {
      if (doc._attachments) {
        Object.keys(doc._attachments).forEach(function (name) {
          attachmentError = attachmentError || attachmentNameError(name);
        });
      }
    });
  
    if (attachmentError) {
      return callback(createError(BAD_REQUEST, attachmentError));
    }
  
    if (!('new_edits' in opts)) {
      if ('new_edits' in req) {
        opts.new_edits = req.new_edits;
      } else {
        opts.new_edits = true;
      }
    }
  
    if (!opts.new_edits && this.type() !== 'http') {
      // ensure revisions of the same doc are sorted, so that
      // the local adapter processes them correctly (#2935)
      req.docs.sort(compareByIdThenRev);
    }
  
    cleanDocs(req.docs);
  
    return this._bulkDocs(req, opts, function (err, res) {
      if (err) {
        return callback(err);
      }
      if (!opts.new_edits) {
        // this is what couch does when new_edits is false
        res = res.filter(function (x) {
          return x.error;
        });
      }
      callback(null, res);
    });
  });
  
  AbstractPouchDB.prototype.registerDependentDatabase =
    adapterFun('registerDependentDatabase', function (dependentDb,
                                                            callback) {
    var depDB = new this.constructor(dependentDb, this.__opts);
  
    function diffFun(doc) {
      doc.dependentDbs = doc.dependentDbs || {};
      if (doc.dependentDbs[dependentDb]) {
        return false; // no update required
      }
      doc.dependentDbs[dependentDb] = true;
      return doc;
    }
    upsert(this, '_local/_pouch_dependentDbs', diffFun)
      .then(function () {
        callback(null, {db: depDB});
      })["catch"](callback);
  });
  
  AbstractPouchDB.prototype.destroy =
    adapterFun('destroy', function (opts, callback) {
  
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
  
    var self = this;
    var usePrefix = 'use_prefix' in self ? self.use_prefix : true;
  
    function destroyDb() {
      // call destroy method of the particular adaptor
      self._destroy(opts, function (err, resp) {
        if (err) {
          return callback(err);
        }
        self._destroyed = true;
        self.emit('destroyed');
        callback(null, resp || { 'ok': true });
      });
    }
  
    if (self.type() === 'http') {
      // no need to check for dependent DBs if it's a remote DB
      return destroyDb();
    }
  
    self.get('_local/_pouch_dependentDbs', function (err, localDoc) {
      if (err) {
        /* istanbul ignore if */
        if (err.status !== 404) {
          return callback(err);
        } else { // no dependencies
          return destroyDb();
        }
      }
      var dependentDbs = localDoc.dependentDbs;
      var PouchDB = self.constructor;
      var deletedMap = Object.keys(dependentDbs).map(function (name) {
        // use_prefix is only false in the browser
        /* istanbul ignore next */
        var trueName = usePrefix ?
          name.replace(new RegExp('^' + PouchDB.prefix), '') : name;
        return new PouchDB(trueName, self.__opts).destroy();
      });
      PouchPromise.all(deletedMap).then(destroyDb, callback);
    });
  });
  
  function TaskQueue() {
    this.isReady = false;
    this.failed = false;
    this.queue = [];
  }
  
  TaskQueue.prototype.execute = function () {
    var fun;
    if (this.failed) {
      while ((fun = this.queue.shift())) {
        fun(this.failed);
      }
    } else {
      while ((fun = this.queue.shift())) {
        fun();
      }
    }
  };
  
  TaskQueue.prototype.fail = function (err) {
    this.failed = err;
    this.execute();
  };
  
  TaskQueue.prototype.ready = function (db) {
    this.isReady = true;
    this.db = db;
    this.execute();
  };
  
  TaskQueue.prototype.addTask = function (fun) {
    this.queue.push(fun);
    if (this.failed) {
      this.execute();
    }
  };
  
  function parseAdapter(name, opts) {
    var match = name.match(/([a-z\-]*):\/\/(.*)/);
    if (match) {
      // the http adapter expects the fully qualified name
      name = /http(s?)/.test(match[1]) ? match[1] + '://' + match[2] : match[2];
      return {name: name, adapter: match[1]};
    }
  
    // check for browsers that have been upgraded from websql-only to websql+idb
    var skipIdb = 'idb' in PouchDB.adapters && 'websql' in PouchDB.adapters &&
      hasLocalStorage() &&
      localStorage['_pouch__websqldb_' + PouchDB.prefix + name];
  
    var adapterName;
  
    if (opts.adapter) {
      adapterName = opts.adapter;
    } else if (typeof opts !== 'undefined' && opts.db) {
      adapterName = 'leveldb';
    } else { // automatically determine adapter
      for (var i = 0; i < PouchDB.preferredAdapters.length; ++i) {
        adapterName = PouchDB.preferredAdapters[i];
        /* istanbul ignore if */
        if (skipIdb && adapterName === 'idb') {
          // log it, because this can be confusing during development
          guardedConsole('log', 'PouchDB is downgrading "' + name + '" to WebSQL to' +
            ' avoid data loss, because it was already opened with WebSQL.');
          continue; // keep using websql to avoid user data loss
        }
        break;
      }
    }
  
    var adapter = PouchDB.adapters[adapterName];
  
    // if adapter is invalid, then an error will be thrown later
    var usePrefix = (adapter && 'use_prefix' in adapter) ?
      adapter.use_prefix : true;
  
    return {
      name: usePrefix ? (PouchDB.prefix + name) : name,
      adapter: adapterName
    };
  }
  
  // OK, so here's the deal. Consider this code:
  //     var db1 = new PouchDB('foo');
  //     var db2 = new PouchDB('foo');
  //     db1.destroy();
  // ^ these two both need to emit 'destroyed' events,
  // as well as the PouchDB constructor itself.
  // So we have one db object (whichever one got destroy() called on it)
  // responsible for emitting the initial event, which then gets emitted
  // by the constructor, which then broadcasts it to any other dbs
  // that may have been created with the same name.
  function prepareForDestruction(self) {
  
    var destructionListeners = self.constructor._destructionListeners;
  
    function onDestroyed() {
      self.constructor.emit('destroyed', self.name);
    }
  
    function onConstructorDestroyed() {
      self.removeListener('destroyed', onDestroyed);
      self.emit('destroyed', self);
    }
  
    self.once('destroyed', onDestroyed);
  
    // in setup.js, the constructor is primed to listen for destroy events
    if (!destructionListeners.has(self.name)) {
      destructionListeners.set(self.name, []);
    }
    destructionListeners.get(self.name).push(onConstructorDestroyed);
  }
  
  inherits(PouchDB, AbstractPouchDB);
  function PouchDB(name, opts) {
    // In Node our test suite only tests this for PouchAlt unfortunately
    /* istanbul ignore if */
    if (!(this instanceof PouchDB)) {
      return new PouchDB(name, opts);
    }
  
    var self = this;
    opts = opts || {};
  
    if (name && typeof name === 'object') {
      opts = name;
      name = opts.name;
      delete opts.name;
    }
  
    this.__opts = opts = clone(opts);
  
    self.auto_compaction = opts.auto_compaction;
    self.prefix = PouchDB.prefix;
  
    if (typeof name !== 'string') {
      throw new Error('Missing/invalid DB name');
    }
  
    var prefixedName = (opts.prefix || '') + name;
    var backend = parseAdapter(prefixedName, opts);
  
    opts.name = backend.name;
    opts.adapter = opts.adapter || backend.adapter;
  
    self.name = name;
    self._adapter = opts.adapter;
    debug('pouchdb:adapter')('Picked adapter: ' + opts.adapter);
  
    if (!PouchDB.adapters[opts.adapter] ||
        !PouchDB.adapters[opts.adapter].valid()) {
      throw new Error('Invalid Adapter: ' + opts.adapter);
    }
  
    AbstractPouchDB.call(self);
    self.taskqueue = new TaskQueue();
  
    self.adapter = opts.adapter;
  
    PouchDB.adapters[opts.adapter].call(self, opts, function (err) {
      if (err) {
        return self.taskqueue.fail(err);
      }
      prepareForDestruction(self);
  
      self.emit('created', self);
      PouchDB.emit('created', self.name);
      self.taskqueue.ready(self);
    });
  
  }
  
  PouchDB.debug = debug;
  
  PouchDB.adapters = {};
  PouchDB.preferredAdapters = [];
  
  PouchDB.prefix = '_pouch_';
  
  var eventEmitter = new events.EventEmitter();
  
  function setUpEventEmitter(Pouch) {
    Object.keys(events.EventEmitter.prototype).forEach(function (key) {
      if (typeof events.EventEmitter.prototype[key] === 'function') {
        Pouch[key] = eventEmitter[key].bind(eventEmitter);
      }
    });
  
    // these are created in constructor.js, and allow us to notify each DB with
    // the same name that it was destroyed, via the constructor object
    var destructListeners = Pouch._destructionListeners = new _Map();
    Pouch.on('destroyed', function onConstructorDestroyed(name) {
      destructListeners.get(name).forEach(function (callback) {
        callback();
      });
      destructListeners["delete"](name);
    });
  }
  
  setUpEventEmitter(PouchDB);
  
  PouchDB.adapter = function (id, obj, addToPreferredAdapters) {
    /* istanbul ignore else */
    if (obj.valid()) {
      PouchDB.adapters[id] = obj;
      if (addToPreferredAdapters) {
        PouchDB.preferredAdapters.push(id);
      }
    }
  };
  
  PouchDB.plugin = function (obj) {
    if (typeof obj === 'function') { // function style for plugins
      obj(PouchDB);
    } else if (typeof obj !== 'object' || Object.keys(obj).length === 0){
      throw new Error('Invalid plugin: object passed in is empty or not an object');
    } else {
      Object.keys(obj).forEach(function (id) { // object style for plugins
        PouchDB.prototype[id] = obj[id];
      });
    }
    return PouchDB;
  };
  
  PouchDB.defaults = function (defaultOpts) {
    function PouchAlt(name, opts) {
      if (!(this instanceof PouchAlt)) {
        return new PouchAlt(name, opts);
      }
  
      opts = opts || {};
  
      if (name && typeof name === 'object') {
        opts = name;
        name = opts.name;
        delete opts.name;
      }
  
      opts = jsExtend.extend({}, defaultOpts, opts);
      PouchDB.call(this, name, opts);
    }
  
    inherits(PouchAlt, PouchDB);
  
    PouchAlt.preferredAdapters = PouchDB.preferredAdapters.slice();
    Object.keys(PouchDB).forEach(function (key) {
      if (!(key in PouchAlt)) {
        PouchAlt[key] = PouchDB[key];
      }
    });
  
    return PouchAlt;
  };
  
  // managed automatically by set-version.js
  var version = "6.0.5";
  
  PouchDB.version = version;
  
  function toObject(array) {
    return array.reduce(function (obj, item) {
      obj[item] = true;
      return obj;
    }, {});
  }
  // List of top level reserved words for doc
  var reservedWords = toObject([
    '_id',
    '_rev',
    '_attachments',
    '_deleted',
    '_revisions',
    '_revs_info',
    '_conflicts',
    '_deleted_conflicts',
    '_local_seq',
    '_rev_tree',
    //replication documents
    '_replication_id',
    '_replication_state',
    '_replication_state_time',
    '_replication_state_reason',
    '_replication_stats',
    // Specific to Couchbase Sync Gateway
    '_removed'
  ]);
  
  // List of reserved words that should end up the document
  var dataWords = toObject([
    '_attachments',
    //replication documents
    '_replication_id',
    '_replication_state',
    '_replication_state_time',
    '_replication_state_reason',
    '_replication_stats'
  ]);
  
  function parseRevisionInfo(rev) {
    if (!/^\d+\-./.test(rev)) {
      return createError(INVALID_REV);
    }
    var idx = rev.indexOf('-');
    var left = rev.substring(0, idx);
    var right = rev.substring(idx + 1);
    return {
      prefix: parseInt(left, 10),
      id: right
    };
  }
  
  function makeRevTreeFromRevisions(revisions, opts) {
    var pos = revisions.start - revisions.ids.length + 1;
  
    var revisionIds = revisions.ids;
    var ids = [revisionIds[0], opts, []];
  
    for (var i = 1, len = revisionIds.length; i < len; i++) {
      ids = [revisionIds[i], {status: 'missing'}, [ids]];
    }
  
    return [{
      pos: pos,
      ids: ids
    }];
  }
  
  // Preprocess documents, parse their revisions, assign an id and a
  // revision for new writes that are missing them, etc
  function parseDoc(doc, newEdits) {
  
    var nRevNum;
    var newRevId;
    var revInfo;
    var opts = {status: 'available'};
    if (doc._deleted) {
      opts.deleted = true;
    }
  
    if (newEdits) {
      if (!doc._id) {
        doc._id = uuid();
      }
      newRevId = uuid(32, 16).toLowerCase();
      if (doc._rev) {
        revInfo = parseRevisionInfo(doc._rev);
        if (revInfo.error) {
          return revInfo;
        }
        doc._rev_tree = [{
          pos: revInfo.prefix,
          ids: [revInfo.id, {status: 'missing'}, [[newRevId, opts, []]]]
        }];
        nRevNum = revInfo.prefix + 1;
      } else {
        doc._rev_tree = [{
          pos: 1,
          ids : [newRevId, opts, []]
        }];
        nRevNum = 1;
      }
    } else {
      if (doc._revisions) {
        doc._rev_tree = makeRevTreeFromRevisions(doc._revisions, opts);
        nRevNum = doc._revisions.start;
        newRevId = doc._revisions.ids[0];
      }
      if (!doc._rev_tree) {
        revInfo = parseRevisionInfo(doc._rev);
        if (revInfo.error) {
          return revInfo;
        }
        nRevNum = revInfo.prefix;
        newRevId = revInfo.id;
        doc._rev_tree = [{
          pos: nRevNum,
          ids: [newRevId, opts, []]
        }];
      }
    }
  
    invalidIdError(doc._id);
  
    doc._rev = nRevNum + '-' + newRevId;
  
    var result = {metadata : {}, data : {}};
    for (var key in doc) {
      /* istanbul ignore else */
      if (Object.prototype.hasOwnProperty.call(doc, key)) {
        var specialKey = key[0] === '_';
        if (specialKey && !reservedWords[key]) {
          var error = createError(DOC_VALIDATION, key);
          error.message = DOC_VALIDATION.message + ': ' + key;
          throw error;
        } else if (specialKey && !dataWords[key]) {
          result.metadata[key.slice(1)] = doc[key];
        } else {
          result.data[key] = doc[key];
        }
      }
    }
    return result;
  }
  
  var atob$1 = function (str) {
    return atob(str);
  };
  
  var btoa$1 = function (str) {
    return btoa(str);
  };
  
  // Abstracts constructing a Blob object, so it also works in older
  // browsers that don't support the native Blob constructor (e.g.
  // old QtWebKit versions, Android < 4.4).
  function createBlob(parts, properties) {
    /* global BlobBuilder,MSBlobBuilder,MozBlobBuilder,WebKitBlobBuilder */
    parts = parts || [];
    properties = properties || {};
    try {
      return new Blob(parts, properties);
    } catch (e) {
      if (e.name !== "TypeError") {
        throw e;
      }
      var Builder = typeof BlobBuilder !== 'undefined' ? BlobBuilder :
                    typeof MSBlobBuilder !== 'undefined' ? MSBlobBuilder :
                    typeof MozBlobBuilder !== 'undefined' ? MozBlobBuilder :
                    WebKitBlobBuilder;
      var builder = new Builder();
      for (var i = 0; i < parts.length; i += 1) {
        builder.append(parts[i]);
      }
      return builder.getBlob(properties.type);
    }
  }
  
  // From http://stackoverflow.com/questions/14967647/ (continues on next line)
  // encode-decode-image-with-base64-breaks-image (2013-04-21)
  function binaryStringToArrayBuffer(bin) {
    var length = bin.length;
    var buf = new ArrayBuffer(length);
    var arr = new Uint8Array(buf);
    for (var i = 0; i < length; i++) {
      arr[i] = bin.charCodeAt(i);
    }
    return buf;
  }
  
  function binStringToBluffer(binString, type) {
    return createBlob([binaryStringToArrayBuffer(binString)], {type: type});
  }
  
  function b64ToBluffer(b64, type) {
    return binStringToBluffer(atob$1(b64), type);
  }
  
  //Can't find original post, but this is close
  //http://stackoverflow.com/questions/6965107/ (continues on next line)
  //converting-between-strings-and-arraybuffers
  function arrayBufferToBinaryString(buffer) {
    var binary = '';
    var bytes = new Uint8Array(buffer);
    var length = bytes.byteLength;
    for (var i = 0; i < length; i++) {
      binary += String.fromCharCode(bytes[i]);
    }
    return binary;
  }
  
  // shim for browsers that don't support it
  function readAsBinaryString(blob, callback) {
    if (typeof FileReader === 'undefined') {
      // fix for Firefox in a web worker
      // https://bugzilla.mozilla.org/show_bug.cgi?id=901097
      return callback(arrayBufferToBinaryString(
        new FileReaderSync().readAsArrayBuffer(blob)));
    }
  
    var reader = new FileReader();
    var hasBinaryString = typeof reader.readAsBinaryString === 'function';
    reader.onloadend = function (e) {
      var result = e.target.result || '';
      if (hasBinaryString) {
        return callback(result);
      }
      callback(arrayBufferToBinaryString(result));
    };
    if (hasBinaryString) {
      reader.readAsBinaryString(blob);
    } else {
      reader.readAsArrayBuffer(blob);
    }
  }
  
  function blobToBinaryString(blobOrBuffer, callback) {
    readAsBinaryString(blobOrBuffer, function (bin) {
      callback(bin);
    });
  }
  
  function blobToBase64(blobOrBuffer, callback) {
    blobToBinaryString(blobOrBuffer, function (base64) {
      callback(btoa$1(base64));
    });
  }
  
  // simplified API. universal browser support is assumed
  function readAsArrayBuffer(blob, callback) {
    if (typeof FileReader === 'undefined') {
      // fix for Firefox in a web worker:
      // https://bugzilla.mozilla.org/show_bug.cgi?id=901097
      return callback(new FileReaderSync().readAsArrayBuffer(blob));
    }
  
    var reader = new FileReader();
    reader.onloadend = function (e) {
      var result = e.target.result || new ArrayBuffer(0);
      callback(result);
    };
    reader.readAsArrayBuffer(blob);
  }
  
  var setImmediateShim = global.setImmediate || global.setTimeout;
  var MD5_CHUNK_SIZE = 32768;
  
  function rawToBase64(raw) {
    return btoa$1(raw);
  }
  
  function sliceBlob(blob, start, end) {
    if (blob.webkitSlice) {
      return blob.webkitSlice(start, end);
    }
    return blob.slice(start, end);
  }
  
  function appendBlob(buffer, blob, start, end, callback) {
    if (start > 0 || end < blob.size) {
      // only slice blob if we really need to
      blob = sliceBlob(blob, start, end);
    }
    readAsArrayBuffer(blob, function (arrayBuffer) {
      buffer.append(arrayBuffer);
      callback();
    });
  }
  
  function appendString(buffer, string, start, end, callback) {
    if (start > 0 || end < string.length) {
      // only create a substring if we really need to
      string = string.substring(start, end);
    }
    buffer.appendBinary(string);
    callback();
  }
  
  function binaryMd5(data, callback) {
    var inputIsString = typeof data === 'string';
    var len = inputIsString ? data.length : data.size;
    var chunkSize = Math.min(MD5_CHUNK_SIZE, len);
    var chunks = Math.ceil(len / chunkSize);
    var currentChunk = 0;
    var buffer = inputIsString ? new Md5() : new Md5.ArrayBuffer();
  
    var append = inputIsString ? appendString : appendBlob;
  
    function next() {
      setImmediateShim(loadNextChunk);
    }
  
    function done() {
      var raw = buffer.end(true);
      var base64 = rawToBase64(raw);
      callback(base64);
      buffer.destroy();
    }
  
    function loadNextChunk() {
      var start = currentChunk * chunkSize;
      var end = start + chunkSize;
      currentChunk++;
      if (currentChunk < chunks) {
        append(buffer, data, start, end, next);
      } else {
        append(buffer, data, start, end, done);
      }
    }
    loadNextChunk();
  }
  
  function stringMd5(string) {
    return Md5.hash(string);
  }
  
  function parseBase64(data) {
    try {
      return atob$1(data);
    } catch (e) {
      var err = createError(BAD_ARG,
        'Attachment is not a valid base64 string');
      return {error: err};
    }
  }
  
  function preprocessString(att, blobType, callback) {
    var asBinary = parseBase64(att.data);
    if (asBinary.error) {
      return callback(asBinary.error);
    }
  
    att.length = asBinary.length;
    if (blobType === 'blob') {
      att.data = binStringToBluffer(asBinary, att.content_type);
    } else if (blobType === 'base64') {
      att.data = btoa$1(asBinary);
    } else { // binary
      att.data = asBinary;
    }
    binaryMd5(asBinary, function (result) {
      att.digest = 'md5-' + result;
      callback();
    });
  }
  
  function preprocessBlob(att, blobType, callback) {
    binaryMd5(att.data, function (md5) {
      att.digest = 'md5-' + md5;
      // size is for blobs (browser), length is for buffers (node)
      att.length = att.data.size || att.data.length || 0;
      if (blobType === 'binary') {
        blobToBinaryString(att.data, function (binString) {
          att.data = binString;
          callback();
        });
      } else if (blobType === 'base64') {
        blobToBase64(att.data, function (b64) {
          att.data = b64;
          callback();
        });
      } else {
        callback();
      }
    });
  }
  
  function preprocessAttachment(att, blobType, callback) {
    if (att.stub) {
      return callback();
    }
    if (typeof att.data === 'string') { // input is a base64 string
      preprocessString(att, blobType, callback);
    } else { // input is a blob
      preprocessBlob(att, blobType, callback);
    }
  }
  
  function preprocessAttachments(docInfos, blobType, callback) {
  
    if (!docInfos.length) {
      return callback();
    }
  
    var docv = 0;
    var overallErr;
  
    docInfos.forEach(function (docInfo) {
      var attachments = docInfo.data && docInfo.data._attachments ?
        Object.keys(docInfo.data._attachments) : [];
      var recv = 0;
  
      if (!attachments.length) {
        return done();
      }
  
      function processedAttachment(err) {
        overallErr = err;
        recv++;
        if (recv === attachments.length) {
          done();
        }
      }
  
      for (var key in docInfo.data._attachments) {
        if (docInfo.data._attachments.hasOwnProperty(key)) {
          preprocessAttachment(docInfo.data._attachments[key],
            blobType, processedAttachment);
        }
      }
    });
  
    function done() {
      docv++;
      if (docInfos.length === docv) {
        if (overallErr) {
          callback(overallErr);
        } else {
          callback();
        }
      }
    }
  }
  
  function updateDoc(revLimit, prev, docInfo, results,
                     i, cb, writeDoc, newEdits) {
  
    if (revExists(prev.rev_tree, docInfo.metadata.rev)) {
      results[i] = docInfo;
      return cb();
    }
  
    // sometimes this is pre-calculated. historically not always
    var previousWinningRev = prev.winningRev || winningRev(prev);
    var previouslyDeleted = 'deleted' in prev ? prev.deleted :
      isDeleted(prev, previousWinningRev);
    var deleted = 'deleted' in docInfo.metadata ? docInfo.metadata.deleted :
      isDeleted(docInfo.metadata);
    var isRoot = /^1-/.test(docInfo.metadata.rev);
  
    if (previouslyDeleted && !deleted && newEdits && isRoot) {
      var newDoc = docInfo.data;
      newDoc._rev = previousWinningRev;
      newDoc._id = docInfo.metadata.id;
      docInfo = parseDoc(newDoc, newEdits);
    }
  
    var merged = merge(prev.rev_tree, docInfo.metadata.rev_tree[0], revLimit);
  
    var inConflict = newEdits && (((previouslyDeleted && deleted) ||
      (!previouslyDeleted && merged.conflicts !== 'new_leaf') ||
      (previouslyDeleted && !deleted && merged.conflicts === 'new_branch')));
  
    if (inConflict) {
      var err = createError(REV_CONFLICT);
      results[i] = err;
      return cb();
    }
  
    var newRev = docInfo.metadata.rev;
    docInfo.metadata.rev_tree = merged.tree;
    docInfo.stemmedRevs = merged.stemmedRevs || [];
    /* istanbul ignore else */
    if (prev.rev_map) {
      docInfo.metadata.rev_map = prev.rev_map; // used only by leveldb
    }
  
    // recalculate
    var winningRev$$ = winningRev(docInfo.metadata);
    var winningRevIsDeleted = isDeleted(docInfo.metadata, winningRev$$);
  
    // calculate the total number of documents that were added/removed,
    // from the perspective of total_rows/doc_count
    var delta = (previouslyDeleted === winningRevIsDeleted) ? 0 :
      previouslyDeleted < winningRevIsDeleted ? -1 : 1;
  
    var newRevIsDeleted;
    if (newRev === winningRev$$) {
      // if the new rev is the same as the winning rev, we can reuse that value
      newRevIsDeleted = winningRevIsDeleted;
    } else {
      // if they're not the same, then we need to recalculate
      newRevIsDeleted = isDeleted(docInfo.metadata, newRev);
    }
  
    writeDoc(docInfo, winningRev$$, winningRevIsDeleted, newRevIsDeleted,
      true, delta, i, cb);
  }
  
  function rootIsMissing(docInfo) {
    return docInfo.metadata.rev_tree[0].ids[1].status === 'missing';
  }
  
  function processDocs(revLimit, docInfos, api, fetchedDocs, tx, results,
                       writeDoc, opts, overallCallback) {
  
    // Default to 1000 locally
    revLimit = revLimit || 1000;
  
    function insertDoc(docInfo, resultsIdx, callback) {
      // Cant insert new deleted documents
      var winningRev$$ = winningRev(docInfo.metadata);
      var deleted = isDeleted(docInfo.metadata, winningRev$$);
      if ('was_delete' in opts && deleted) {
        results[resultsIdx] = createError(MISSING_DOC, 'deleted');
        return callback();
      }
  
      // 4712 - detect whether a new document was inserted with a _rev
      var inConflict = newEdits && rootIsMissing(docInfo);
  
      if (inConflict) {
        var err = createError(REV_CONFLICT);
        results[resultsIdx] = err;
        return callback();
      }
  
      var delta = deleted ? 0 : 1;
  
      writeDoc(docInfo, winningRev$$, deleted, deleted, false,
        delta, resultsIdx, callback);
    }
  
    var newEdits = opts.new_edits;
    var idsToDocs = new _Map();
  
    var docsDone = 0;
    var docsToDo = docInfos.length;
  
    function checkAllDocsDone() {
      if (++docsDone === docsToDo && overallCallback) {
        overallCallback();
      }
    }
  
    docInfos.forEach(function (currentDoc, resultsIdx) {
  
      if (currentDoc._id && isLocalId(currentDoc._id)) {
        var fun = currentDoc._deleted ? '_removeLocal' : '_putLocal';
        api[fun](currentDoc, {ctx: tx}, function (err, res) {
          results[resultsIdx] = err || res;
          checkAllDocsDone();
        });
        return;
      }
  
      var id = currentDoc.metadata.id;
      if (idsToDocs.has(id)) {
        docsToDo--; // duplicate
        idsToDocs.get(id).push([currentDoc, resultsIdx]);
      } else {
        idsToDocs.set(id, [[currentDoc, resultsIdx]]);
      }
    });
  
    // in the case of new_edits, the user can provide multiple docs
    // with the same id. these need to be processed sequentially
    idsToDocs.forEach(function (docs, id) {
      var numDone = 0;
  
      function docWritten() {
        if (++numDone < docs.length) {
          nextDoc();
        } else {
          checkAllDocsDone();
        }
      }
      function nextDoc() {
        var value = docs[numDone];
        var currentDoc = value[0];
        var resultsIdx = value[1];
  
        if (fetchedDocs.has(id)) {
          updateDoc(revLimit, fetchedDocs.get(id), currentDoc, results,
            resultsIdx, docWritten, writeDoc, newEdits);
        } else {
          // Ensure stemming applies to new writes as well
          var merged = merge([], currentDoc.metadata.rev_tree[0], revLimit);
          currentDoc.metadata.rev_tree = merged.tree;
          currentDoc.stemmedRevs = merged.stemmedRevs || [];
          insertDoc(currentDoc, resultsIdx, docWritten);
        }
      }
      nextDoc();
    });
  }
  
  // IndexedDB requires a versioned database structure, so we use the
  // version here to manage migrations.
  var ADAPTER_VERSION = 5;
  
  // The object stores created for each database
  // DOC_STORE stores the document meta data, its revision history and state
  // Keyed by document id
  var DOC_STORE = 'document-store';
  // BY_SEQ_STORE stores a particular version of a document, keyed by its
  // sequence id
  var BY_SEQ_STORE = 'by-sequence';
  // Where we store attachments
  var ATTACH_STORE = 'attach-store';
  // Where we store many-to-many relations
  // between attachment digests and seqs
  var ATTACH_AND_SEQ_STORE = 'attach-seq-store';
  
  // Where we store database-wide meta data in a single record
  // keyed by id: META_STORE
  var META_STORE = 'meta-store';
  // Where we store local documents
  var LOCAL_STORE = 'local-store';
  // Where we detect blob support
  var DETECT_BLOB_SUPPORT_STORE = 'detect-blob-support';
  
  function slowJsonParse(str) {
    try {
      return JSON.parse(str);
    } catch (e) {
      /* istanbul ignore next */
      return vuvuzela.parse(str);
    }
  }
  
  function safeJsonParse(str) {
    // try/catch is deoptimized in V8, leading to slower
    // times than we'd like to have. Most documents are _not_
    // huge, and do not require a slower code path just to parse them.
    // We can be pretty sure that a document under 50000 characters
    // will not be so deeply nested as to throw a stack overflow error
    // (depends on the engine and available memory, though, so this is
    // just a hunch). 50000 was chosen based on the average length
    // of this string in our test suite, to try to find a number that covers
    // most of our test cases (26 over this size, 26378 under it).
    if (str.length < 50000) {
      return JSON.parse(str);
    }
    return slowJsonParse(str);
  }
  
  function safeJsonStringify(json) {
    try {
      return JSON.stringify(json);
    } catch (e) {
      /* istanbul ignore next */
      return vuvuzela.stringify(json);
    }
  }
  
  function tryCode(fun, that, args, PouchDB) {
    try {
      fun.apply(that, args);
    } catch (err) {
      // Shouldn't happen, but in some odd cases
      // IndexedDB implementations might throw a sync
      // error, in which case this will at least log it.
      PouchDB.emit('error', err);
    }
  }
  
  var taskQueue = {
    running: false,
    queue: []
  };
  
  function applyNext(PouchDB) {
    if (taskQueue.running || !taskQueue.queue.length) {
      return;
    }
    taskQueue.running = true;
    var item = taskQueue.queue.shift();
    item.action(function (err, res) {
      tryCode(item.callback, this, [err, res], PouchDB);
      taskQueue.running = false;
      process.nextTick(function () {
        applyNext(PouchDB);
      });
    });
  }
  
  function idbError(callback) {
    return function (evt) {
      var message = 'unknown_error';
      if (evt.target && evt.target.error) {
        message = evt.target.error.name || evt.target.error.message;
      }
      callback(createError(IDB_ERROR, message, evt.type));
    };
  }
  
  // Unfortunately, the metadata has to be stringified
  // when it is put into the database, because otherwise
  // IndexedDB can throw errors for deeply-nested objects.
  // Originally we just used JSON.parse/JSON.stringify; now
  // we use this custom vuvuzela library that avoids recursion.
  // If we could do it all over again, we'd probably use a
  // format for the revision trees other than JSON.
  function encodeMetadata(metadata, winningRev, deleted) {
    return {
      data: safeJsonStringify(metadata),
      winningRev: winningRev,
      deletedOrLocal: deleted ? '1' : '0',
      seq: metadata.seq, // highest seq for this doc
      id: metadata.id
    };
  }
  
  function decodeMetadata(storedObject) {
    if (!storedObject) {
      return null;
    }
    var metadata = safeJsonParse(storedObject.data);
    metadata.winningRev = storedObject.winningRev;
    metadata.deleted = storedObject.deletedOrLocal === '1';
    metadata.seq = storedObject.seq;
    return metadata;
  }
  
  // read the doc back out from the database. we don't store the
  // _id or _rev because we already have _doc_id_rev.
  function decodeDoc(doc) {
    if (!doc) {
      return doc;
    }
    var idx = doc._doc_id_rev.lastIndexOf(':');
    doc._id = doc._doc_id_rev.substring(0, idx - 1);
    doc._rev = doc._doc_id_rev.substring(idx + 1);
    delete doc._doc_id_rev;
    return doc;
  }
  
  // Read a blob from the database, encoding as necessary
  // and translating from base64 if the IDB doesn't support
  // native Blobs
  function readBlobData(body, type, asBlob, callback) {
    if (asBlob) {
      if (!body) {
        callback(createBlob([''], {type: type}));
      } else if (typeof body !== 'string') { // we have blob support
        callback(body);
      } else { // no blob support
        callback(b64ToBluffer(body, type));
      }
    } else { // as base64 string
      if (!body) {
        callback('');
      } else if (typeof body !== 'string') { // we have blob support
        readAsBinaryString(body, function (binary) {
          callback(btoa$1(binary));
        });
      } else { // no blob support
        callback(body);
      }
    }
  }
  
  function fetchAttachmentsIfNecessary(doc, opts, txn, cb) {
    var attachments = Object.keys(doc._attachments || {});
    if (!attachments.length) {
      return cb && cb();
    }
    var numDone = 0;
  
    function checkDone() {
      if (++numDone === attachments.length && cb) {
        cb();
      }
    }
  
    function fetchAttachment(doc, att) {
      var attObj = doc._attachments[att];
      var digest = attObj.digest;
      var req = txn.objectStore(ATTACH_STORE).get(digest);
      req.onsuccess = function (e) {
        attObj.body = e.target.result.body;
        checkDone();
      };
    }
  
    attachments.forEach(function (att) {
      if (opts.attachments && opts.include_docs) {
        fetchAttachment(doc, att);
      } else {
        doc._attachments[att].stub = true;
        checkDone();
      }
    });
  }
  
  // IDB-specific postprocessing necessary because
  // we don't know whether we stored a true Blob or
  // a base64-encoded string, and if it's a Blob it
  // needs to be read outside of the transaction context
  function postProcessAttachments(results, asBlob) {
    return PouchPromise.all(results.map(function (row) {
      if (row.doc && row.doc._attachments) {
        var attNames = Object.keys(row.doc._attachments);
        return PouchPromise.all(attNames.map(function (att) {
          var attObj = row.doc._attachments[att];
          if (!('body' in attObj)) { // already processed
            return;
          }
          var body = attObj.body;
          var type = attObj.content_type;
          return new PouchPromise(function (resolve) {
            readBlobData(body, type, asBlob, function (data) {
              row.doc._attachments[att] = jsExtend.extend(
                pick(attObj, ['digest', 'content_type']),
                {data: data}
              );
              resolve();
            });
          });
        }));
      }
    }));
  }
  
  function compactRevs(revs, docId, txn) {
  
    var possiblyOrphanedDigests = [];
    var seqStore = txn.objectStore(BY_SEQ_STORE);
    var attStore = txn.objectStore(ATTACH_STORE);
    var attAndSeqStore = txn.objectStore(ATTACH_AND_SEQ_STORE);
    var count = revs.length;
  
    function checkDone() {
      count--;
      if (!count) { // done processing all revs
        deleteOrphanedAttachments();
      }
    }
  
    function deleteOrphanedAttachments() {
      if (!possiblyOrphanedDigests.length) {
        return;
      }
      possiblyOrphanedDigests.forEach(function (digest) {
        var countReq = attAndSeqStore.index('digestSeq').count(
          IDBKeyRange.bound(
            digest + '::', digest + '::\uffff', false, false));
        countReq.onsuccess = function (e) {
          var count = e.target.result;
          if (!count) {
            // orphaned
            attStore["delete"](digest);
          }
        };
      });
    }
  
    revs.forEach(function (rev) {
      var index = seqStore.index('_doc_id_rev');
      var key = docId + "::" + rev;
      index.getKey(key).onsuccess = function (e) {
        var seq = e.target.result;
        if (typeof seq !== 'number') {
          return checkDone();
        }
        seqStore["delete"](seq);
  
        var cursor = attAndSeqStore.index('seq')
          .openCursor(IDBKeyRange.only(seq));
  
        cursor.onsuccess = function (event) {
          var cursor = event.target.result;
          if (cursor) {
            var digest = cursor.value.digestSeq.split('::')[0];
            possiblyOrphanedDigests.push(digest);
            attAndSeqStore["delete"](cursor.primaryKey);
            cursor["continue"]();
          } else { // done
            checkDone();
          }
        };
      };
    });
  }
  
  function openTransactionSafely(idb, stores, mode) {
    try {
      return {
        txn: idb.transaction(stores, mode)
      };
    } catch (err) {
      return {
        error: err
      };
    }
  }
  
  function idbBulkDocs(dbOpts, req, opts, api, idb, idbChanges, callback) {
    var docInfos = req.docs;
    var txn;
    var docStore;
    var bySeqStore;
    var attachStore;
    var attachAndSeqStore;
    var docInfoError;
    var docCountDelta = 0;
  
    for (var i = 0, len = docInfos.length; i < len; i++) {
      var doc = docInfos[i];
      if (doc._id && isLocalId(doc._id)) {
        continue;
      }
      doc = docInfos[i] = parseDoc(doc, opts.new_edits);
      if (doc.error && !docInfoError) {
        docInfoError = doc;
      }
    }
  
    if (docInfoError) {
      return callback(docInfoError);
    }
  
    var results = new Array(docInfos.length);
    var fetchedDocs = new _Map();
    var preconditionErrored = false;
    var blobType = api._meta.blobSupport ? 'blob' : 'base64';
  
    preprocessAttachments(docInfos, blobType, function (err) {
      if (err) {
        return callback(err);
      }
      startTransaction();
    });
  
    function startTransaction() {
  
      var stores = [
        DOC_STORE, BY_SEQ_STORE,
        ATTACH_STORE,
        LOCAL_STORE, ATTACH_AND_SEQ_STORE
      ];
      var txnResult = openTransactionSafely(idb, stores, 'readwrite');
      if (txnResult.error) {
        return callback(txnResult.error);
      }
      txn = txnResult.txn;
      txn.onabort = idbError(callback);
      txn.ontimeout = idbError(callback);
      txn.oncomplete = complete;
      docStore = txn.objectStore(DOC_STORE);
      bySeqStore = txn.objectStore(BY_SEQ_STORE);
      attachStore = txn.objectStore(ATTACH_STORE);
      attachAndSeqStore = txn.objectStore(ATTACH_AND_SEQ_STORE);
  
      verifyAttachments(function (err) {
        if (err) {
          preconditionErrored = true;
          return callback(err);
        }
        fetchExistingDocs();
      });
    }
  
    function idbProcessDocs() {
      processDocs(dbOpts.revs_limit, docInfos, api, fetchedDocs,
                  txn, results, writeDoc, opts);
    }
  
    function fetchExistingDocs() {
  
      if (!docInfos.length) {
        return;
      }
  
      var numFetched = 0;
  
      function checkDone() {
        if (++numFetched === docInfos.length) {
          idbProcessDocs();
        }
      }
  
      function readMetadata(event) {
        var metadata = decodeMetadata(event.target.result);
  
        if (metadata) {
          fetchedDocs.set(metadata.id, metadata);
        }
        checkDone();
      }
  
      for (var i = 0, len = docInfos.length; i < len; i++) {
        var docInfo = docInfos[i];
        if (docInfo._id && isLocalId(docInfo._id)) {
          checkDone(); // skip local docs
          continue;
        }
        var req = docStore.get(docInfo.metadata.id);
        req.onsuccess = readMetadata;
      }
    }
  
    function complete() {
      if (preconditionErrored) {
        return;
      }
  
      idbChanges.notify(api._meta.name);
      api._meta.docCount += docCountDelta;
      callback(null, results);
    }
  
    function verifyAttachment(digest, callback) {
  
      var req = attachStore.get(digest);
      req.onsuccess = function (e) {
        if (!e.target.result) {
          var err = createError(MISSING_STUB,
            'unknown stub attachment with digest ' +
            digest);
          err.status = 412;
          callback(err);
        } else {
          callback();
        }
      };
    }
  
    function verifyAttachments(finish) {
  
  
      var digests = [];
      docInfos.forEach(function (docInfo) {
        if (docInfo.data && docInfo.data._attachments) {
          Object.keys(docInfo.data._attachments).forEach(function (filename) {
            var att = docInfo.data._attachments[filename];
            if (att.stub) {
              digests.push(att.digest);
            }
          });
        }
      });
      if (!digests.length) {
        return finish();
      }
      var numDone = 0;
      var err;
  
      function checkDone() {
        if (++numDone === digests.length) {
          finish(err);
        }
      }
      digests.forEach(function (digest) {
        verifyAttachment(digest, function (attErr) {
          if (attErr && !err) {
            err = attErr;
          }
          checkDone();
        });
      });
    }
  
    function writeDoc(docInfo, winningRev, winningRevIsDeleted, newRevIsDeleted,
                      isUpdate, delta, resultsIdx, callback) {
  
      docCountDelta += delta;
  
      docInfo.metadata.winningRev = winningRev;
      docInfo.metadata.deleted = winningRevIsDeleted;
  
      var doc = docInfo.data;
      doc._id = docInfo.metadata.id;
      doc._rev = docInfo.metadata.rev;
  
      if (newRevIsDeleted) {
        doc._deleted = true;
      }
  
      var hasAttachments = doc._attachments &&
        Object.keys(doc._attachments).length;
      if (hasAttachments) {
        return writeAttachments(docInfo, winningRev, winningRevIsDeleted,
          isUpdate, resultsIdx, callback);
      }
  
      finishDoc(docInfo, winningRev, winningRevIsDeleted,
        isUpdate, resultsIdx, callback);
    }
  
    function finishDoc(docInfo, winningRev, winningRevIsDeleted,
                       isUpdate, resultsIdx, callback) {
  
      var doc = docInfo.data;
      var metadata = docInfo.metadata;
  
      doc._doc_id_rev = metadata.id + '::' + metadata.rev;
      delete doc._id;
      delete doc._rev;
  
      function afterPutDoc(e) {
        var revsToDelete = docInfo.stemmedRevs || [];
  
        if (isUpdate && api.auto_compaction) {
          revsToDelete = revsToDelete.concat(compactTree(docInfo.metadata));
        }
  
        if (revsToDelete && revsToDelete.length) {
          compactRevs(revsToDelete, docInfo.metadata.id, txn);
        }
  
        metadata.seq = e.target.result;
        // Current _rev is calculated from _rev_tree on read
        delete metadata.rev;
        var metadataToStore = encodeMetadata(metadata, winningRev,
          winningRevIsDeleted);
        var metaDataReq = docStore.put(metadataToStore);
        metaDataReq.onsuccess = afterPutMetadata;
      }
  
      function afterPutDocError(e) {
        // ConstraintError, need to update, not put (see #1638 for details)
        e.preventDefault(); // avoid transaction abort
        e.stopPropagation(); // avoid transaction onerror
        var index = bySeqStore.index('_doc_id_rev');
        var getKeyReq = index.getKey(doc._doc_id_rev);
        getKeyReq.onsuccess = function (e) {
          var putReq = bySeqStore.put(doc, e.target.result);
          putReq.onsuccess = afterPutDoc;
        };
      }
  
      function afterPutMetadata() {
        results[resultsIdx] = {
          ok: true,
          id: metadata.id,
          rev: winningRev
        };
        fetchedDocs.set(docInfo.metadata.id, docInfo.metadata);
        insertAttachmentMappings(docInfo, metadata.seq, callback);
      }
  
      var putReq = bySeqStore.put(doc);
  
      putReq.onsuccess = afterPutDoc;
      putReq.onerror = afterPutDocError;
    }
  
    function writeAttachments(docInfo, winningRev, winningRevIsDeleted,
                              isUpdate, resultsIdx, callback) {
  
  
      var doc = docInfo.data;
  
      var numDone = 0;
      var attachments = Object.keys(doc._attachments);
  
      function collectResults() {
        if (numDone === attachments.length) {
          finishDoc(docInfo, winningRev, winningRevIsDeleted,
            isUpdate, resultsIdx, callback);
        }
      }
  
      function attachmentSaved() {
        numDone++;
        collectResults();
      }
  
      attachments.forEach(function (key) {
        var att = docInfo.data._attachments[key];
        if (!att.stub) {
          var data = att.data;
          delete att.data;
          att.revpos = parseInt(winningRev, 10);
          var digest = att.digest;
          saveAttachment(digest, data, attachmentSaved);
        } else {
          numDone++;
          collectResults();
        }
      });
    }
  
    // map seqs to attachment digests, which
    // we will need later during compaction
    function insertAttachmentMappings(docInfo, seq, callback) {
  
      var attsAdded = 0;
      var attsToAdd = Object.keys(docInfo.data._attachments || {});
  
      if (!attsToAdd.length) {
        return callback();
      }
  
      function checkDone() {
        if (++attsAdded === attsToAdd.length) {
          callback();
        }
      }
  
      function add(att) {
        var digest = docInfo.data._attachments[att].digest;
        var req = attachAndSeqStore.put({
          seq: seq,
          digestSeq: digest + '::' + seq
        });
  
        req.onsuccess = checkDone;
        req.onerror = function (e) {
          // this callback is for a constaint error, which we ignore
          // because this docid/rev has already been associated with
          // the digest (e.g. when new_edits == false)
          e.preventDefault(); // avoid transaction abort
          e.stopPropagation(); // avoid transaction onerror
          checkDone();
        };
      }
      for (var i = 0; i < attsToAdd.length; i++) {
        add(attsToAdd[i]); // do in parallel
      }
    }
  
    function saveAttachment(digest, data, callback) {
  
  
      var getKeyReq = attachStore.count(digest);
      getKeyReq.onsuccess = function (e) {
        var count = e.target.result;
        if (count) {
          return callback(); // already exists
        }
        var newAtt = {
          digest: digest,
          body: data
        };
        var putReq = attachStore.put(newAtt);
        putReq.onsuccess = callback;
      };
    }
  }
  
  function createKeyRange(start, end, inclusiveEnd, key, descending) {
    try {
      if (start && end) {
        if (descending) {
          return IDBKeyRange.bound(end, start, !inclusiveEnd, false);
        } else {
          return IDBKeyRange.bound(start, end, false, !inclusiveEnd);
        }
      } else if (start) {
        if (descending) {
          return IDBKeyRange.upperBound(start);
        } else {
          return IDBKeyRange.lowerBound(start);
        }
      } else if (end) {
        if (descending) {
          return IDBKeyRange.lowerBound(end, !inclusiveEnd);
        } else {
          return IDBKeyRange.upperBound(end, !inclusiveEnd);
        }
      } else if (key) {
        return IDBKeyRange.only(key);
      }
    } catch (e) {
      return {error: e};
    }
    return null;
  }
  
  function handleKeyRangeError(api, opts, err, callback) {
    if (err.name === "DataError" && err.code === 0) {
      // data error, start is less than end
      return callback(null, {
        total_rows: api._meta.docCount,
        offset: opts.skip,
        rows: []
      });
    }
    callback(createError(IDB_ERROR, err.name, err.message));
  }
  
  function idbAllDocs(opts, api, idb, callback) {
  
    function allDocsQuery(opts, callback) {
      var start = 'startkey' in opts ? opts.startkey : false;
      var end = 'endkey' in opts ? opts.endkey : false;
      var key = 'key' in opts ? opts.key : false;
      var skip = opts.skip || 0;
      var limit = typeof opts.limit === 'number' ? opts.limit : -1;
      var inclusiveEnd = opts.inclusive_end !== false;
      var descending = 'descending' in opts && opts.descending ? 'prev' : null;
  
      var keyRange = createKeyRange(start, end, inclusiveEnd, key, descending);
      if (keyRange && keyRange.error) {
        return handleKeyRangeError(api, opts, keyRange.error, callback);
      }
  
      var stores = [DOC_STORE, BY_SEQ_STORE];
  
      if (opts.attachments) {
        stores.push(ATTACH_STORE);
      }
      var txnResult = openTransactionSafely(idb, stores, 'readonly');
      if (txnResult.error) {
        return callback(txnResult.error);
      }
      var txn = txnResult.txn;
      var docStore = txn.objectStore(DOC_STORE);
      var seqStore = txn.objectStore(BY_SEQ_STORE);
      var cursor = descending ?
        docStore.openCursor(keyRange, descending) :
        docStore.openCursor(keyRange);
      var docIdRevIndex = seqStore.index('_doc_id_rev');
      var results = [];
      var docCount = 0;
  
      // if the user specifies include_docs=true, then we don't
      // want to block the main cursor while we're fetching the doc
      function fetchDocAsynchronously(metadata, row, winningRev) {
        var key = metadata.id + "::" + winningRev;
        docIdRevIndex.get(key).onsuccess =  function onGetDoc(e) {
          row.doc = decodeDoc(e.target.result);
          if (opts.conflicts) {
            row.doc._conflicts = collectConflicts(metadata);
          }
          fetchAttachmentsIfNecessary(row.doc, opts, txn);
        };
      }
  
      function allDocsInner(cursor, winningRev, metadata) {
        var row = {
          id: metadata.id,
          key: metadata.id,
          value: {
            rev: winningRev
          }
        };
        var deleted = metadata.deleted;
        if (opts.deleted === 'ok') {
          results.push(row);
          // deleted docs are okay with "keys" requests
          if (deleted) {
            row.value.deleted = true;
            row.doc = null;
          } else if (opts.include_docs) {
            fetchDocAsynchronously(metadata, row, winningRev);
          }
        } else if (!deleted && skip-- <= 0) {
          results.push(row);
          if (opts.include_docs) {
            fetchDocAsynchronously(metadata, row, winningRev);
          }
          if (--limit === 0) {
            return;
          }
        }
        cursor["continue"]();
      }
  
      function onGetCursor(e) {
        docCount = api._meta.docCount; // do this within the txn for consistency
        var cursor = e.target.result;
        if (!cursor) {
          return;
        }
        var metadata = decodeMetadata(cursor.value);
        var winningRev = metadata.winningRev;
  
        allDocsInner(cursor, winningRev, metadata);
      }
  
      function onResultsReady() {
        callback(null, {
          total_rows: docCount,
          offset: opts.skip,
          rows: results
        });
      }
  
      function onTxnComplete() {
        if (opts.attachments) {
          postProcessAttachments(results, opts.binary).then(onResultsReady);
        } else {
          onResultsReady();
        }
      }
  
      txn.oncomplete = onTxnComplete;
      cursor.onsuccess = onGetCursor;
    }
  
    function allDocs(opts, callback) {
  
      if (opts.limit === 0) {
        return callback(null, {
          total_rows: api._meta.docCount,
          offset: opts.skip,
          rows: []
        });
      }
      allDocsQuery(opts, callback);
    }
  
    allDocs(opts, callback);
  }
  
  //
  // Blobs are not supported in all versions of IndexedDB, notably
  // Chrome <37 and Android <5. In those versions, storing a blob will throw.
  //
  // Various other blob bugs exist in Chrome v37-42 (inclusive).
  // Detecting them is expensive and confusing to users, and Chrome 37-42
  // is at very low usage worldwide, so we do a hacky userAgent check instead.
  //
  // content-type bug: https://code.google.com/p/chromium/issues/detail?id=408120
  // 404 bug: https://code.google.com/p/chromium/issues/detail?id=447916
  // FileReader bug: https://code.google.com/p/chromium/issues/detail?id=447836
  //
  function checkBlobSupport(txn) {
    return new PouchPromise(function (resolve) {
      var blob = createBlob(['']);
      txn.objectStore(DETECT_BLOB_SUPPORT_STORE).put(blob, 'key');
  
      txn.onabort = function (e) {
        // If the transaction aborts now its due to not being able to
        // write to the database, likely due to the disk being full
        e.preventDefault();
        e.stopPropagation();
        resolve(false);
      };
  
      txn.oncomplete = function () {
        var matchedChrome = navigator.userAgent.match(/Chrome\/(\d+)/);
        var matchedEdge = navigator.userAgent.match(/Edge\//);
        // MS Edge pretends to be Chrome 42:
        // https://msdn.microsoft.com/en-us/library/hh869301%28v=vs.85%29.aspx
        resolve(matchedEdge || !matchedChrome ||
          parseInt(matchedChrome[1], 10) >= 43);
      };
    })["catch"](function () {
      return false; // error, so assume unsupported
    });
  }
  
  var cachedDBs = new _Map();
  var blobSupportPromise;
  var idbChanges = new Changes$1();
  var openReqList = new _Map();
  
  function IdbPouch(opts, callback) {
    var api = this;
  
    taskQueue.queue.push({
      action: function (thisCallback) {
        init(api, opts, thisCallback);
      },
      callback: callback
    });
    applyNext(api.constructor);
  }
  
  function init(api, opts, callback) {
  
    var dbName = opts.name;
  
    var idb = null;
    api._meta = null;
  
    // called when creating a fresh new database
    function createSchema(db) {
      var docStore = db.createObjectStore(DOC_STORE, {keyPath : 'id'});
      db.createObjectStore(BY_SEQ_STORE, {autoIncrement: true})
        .createIndex('_doc_id_rev', '_doc_id_rev', {unique: true});
      db.createObjectStore(ATTACH_STORE, {keyPath: 'digest'});
      db.createObjectStore(META_STORE, {keyPath: 'id', autoIncrement: false});
      db.createObjectStore(DETECT_BLOB_SUPPORT_STORE);
  
      // added in v2
      docStore.createIndex('deletedOrLocal', 'deletedOrLocal', {unique : false});
  
      // added in v3
      db.createObjectStore(LOCAL_STORE, {keyPath: '_id'});
  
      // added in v4
      var attAndSeqStore = db.createObjectStore(ATTACH_AND_SEQ_STORE,
        {autoIncrement: true});
      attAndSeqStore.createIndex('seq', 'seq');
      attAndSeqStore.createIndex('digestSeq', 'digestSeq', {unique: true});
    }
  
    // migration to version 2
    // unfortunately "deletedOrLocal" is a misnomer now that we no longer
    // store local docs in the main doc-store, but whaddyagonnado
    function addDeletedOrLocalIndex(txn, callback) {
      var docStore = txn.objectStore(DOC_STORE);
      docStore.createIndex('deletedOrLocal', 'deletedOrLocal', {unique : false});
  
      docStore.openCursor().onsuccess = function (event) {
        var cursor = event.target.result;
        if (cursor) {
          var metadata = cursor.value;
          var deleted = isDeleted(metadata);
          metadata.deletedOrLocal = deleted ? "1" : "0";
          docStore.put(metadata);
          cursor["continue"]();
        } else {
          callback();
        }
      };
    }
  
    // migration to version 3 (part 1)
    function createLocalStoreSchema(db) {
      db.createObjectStore(LOCAL_STORE, {keyPath: '_id'})
        .createIndex('_doc_id_rev', '_doc_id_rev', {unique: true});
    }
  
    // migration to version 3 (part 2)
    function migrateLocalStore(txn, cb) {
      var localStore = txn.objectStore(LOCAL_STORE);
      var docStore = txn.objectStore(DOC_STORE);
      var seqStore = txn.objectStore(BY_SEQ_STORE);
  
      var cursor = docStore.openCursor();
      cursor.onsuccess = function (event) {
        var cursor = event.target.result;
        if (cursor) {
          var metadata = cursor.value;
          var docId = metadata.id;
          var local = isLocalId(docId);
          var rev = winningRev(metadata);
          if (local) {
            var docIdRev = docId + "::" + rev;
            // remove all seq entries
            // associated with this docId
            var start = docId + "::";
            var end = docId + "::~";
            var index = seqStore.index('_doc_id_rev');
            var range = IDBKeyRange.bound(start, end, false, false);
            var seqCursor = index.openCursor(range);
            seqCursor.onsuccess = function (e) {
              seqCursor = e.target.result;
              if (!seqCursor) {
                // done
                docStore["delete"](cursor.primaryKey);
                cursor["continue"]();
              } else {
                var data = seqCursor.value;
                if (data._doc_id_rev === docIdRev) {
                  localStore.put(data);
                }
                seqStore["delete"](seqCursor.primaryKey);
                seqCursor["continue"]();
              }
            };
          } else {
            cursor["continue"]();
          }
        } else if (cb) {
          cb();
        }
      };
    }
  
    // migration to version 4 (part 1)
    function addAttachAndSeqStore(db) {
      var attAndSeqStore = db.createObjectStore(ATTACH_AND_SEQ_STORE,
        {autoIncrement: true});
      attAndSeqStore.createIndex('seq', 'seq');
      attAndSeqStore.createIndex('digestSeq', 'digestSeq', {unique: true});
    }
  
    // migration to version 4 (part 2)
    function migrateAttsAndSeqs(txn, callback) {
      var seqStore = txn.objectStore(BY_SEQ_STORE);
      var attStore = txn.objectStore(ATTACH_STORE);
      var attAndSeqStore = txn.objectStore(ATTACH_AND_SEQ_STORE);
  
      // need to actually populate the table. this is the expensive part,
      // so as an optimization, check first that this database even
      // contains attachments
      var req = attStore.count();
      req.onsuccess = function (e) {
        var count = e.target.result;
        if (!count) {
          return callback(); // done
        }
  
        seqStore.openCursor().onsuccess = function (e) {
          var cursor = e.target.result;
          if (!cursor) {
            return callback(); // done
          }
          var doc = cursor.value;
          var seq = cursor.primaryKey;
          var atts = Object.keys(doc._attachments || {});
          var digestMap = {};
          for (var j = 0; j < atts.length; j++) {
            var att = doc._attachments[atts[j]];
            digestMap[att.digest] = true; // uniq digests, just in case
          }
          var digests = Object.keys(digestMap);
          for (j = 0; j < digests.length; j++) {
            var digest = digests[j];
            attAndSeqStore.put({
              seq: seq,
              digestSeq: digest + '::' + seq
            });
          }
          cursor["continue"]();
        };
      };
    }
  
    // migration to version 5
    // Instead of relying on on-the-fly migration of metadata,
    // this brings the doc-store to its modern form:
    // - metadata.winningrev
    // - metadata.seq
    // - stringify the metadata when storing it
    function migrateMetadata(txn) {
  
      function decodeMetadataCompat(storedObject) {
        if (!storedObject.data) {
          // old format, when we didn't store it stringified
          storedObject.deleted = storedObject.deletedOrLocal === '1';
          return storedObject;
        }
        return decodeMetadata(storedObject);
      }
  
      // ensure that every metadata has a winningRev and seq,
      // which was previously created on-the-fly but better to migrate
      var bySeqStore = txn.objectStore(BY_SEQ_STORE);
      var docStore = txn.objectStore(DOC_STORE);
      var cursor = docStore.openCursor();
      cursor.onsuccess = function (e) {
        var cursor = e.target.result;
        if (!cursor) {
          return; // done
        }
        var metadata = decodeMetadataCompat(cursor.value);
  
        metadata.winningRev = metadata.winningRev ||
          winningRev(metadata);
  
        function fetchMetadataSeq() {
          // metadata.seq was added post-3.2.0, so if it's missing,
          // we need to fetch it manually
          var start = metadata.id + '::';
          var end = metadata.id + '::\uffff';
          var req = bySeqStore.index('_doc_id_rev').openCursor(
            IDBKeyRange.bound(start, end));
  
          var metadataSeq = 0;
          req.onsuccess = function (e) {
            var cursor = e.target.result;
            if (!cursor) {
              metadata.seq = metadataSeq;
              return onGetMetadataSeq();
            }
            var seq = cursor.primaryKey;
            if (seq > metadataSeq) {
              metadataSeq = seq;
            }
            cursor["continue"]();
          };
        }
  
        function onGetMetadataSeq() {
          var metadataToStore = encodeMetadata(metadata,
            metadata.winningRev, metadata.deleted);
  
          var req = docStore.put(metadataToStore);
          req.onsuccess = function () {
            cursor["continue"]();
          };
        }
  
        if (metadata.seq) {
          return onGetMetadataSeq();
        }
  
        fetchMetadataSeq();
      };
  
    }
  
    api.type = function () {
      return 'idb';
    };
  
    api._id = toPromise(function (callback) {
      callback(null, api._meta.instanceId);
    });
  
    api._bulkDocs = function idb_bulkDocs(req, reqOpts, callback) {
      idbBulkDocs(opts, req, reqOpts, api, idb, idbChanges, callback);
    };
  
    // First we look up the metadata in the ids database, then we fetch the
    // current revision(s) from the by sequence store
    api._get = function idb_get(id, opts, callback) {
      var doc;
      var metadata;
      var err;
      var txn = opts.ctx;
      if (!txn) {
        var txnResult = openTransactionSafely(idb,
          [DOC_STORE, BY_SEQ_STORE, ATTACH_STORE], 'readonly');
        if (txnResult.error) {
          return callback(txnResult.error);
        }
        txn = txnResult.txn;
      }
  
      function finish() {
        callback(err, {doc: doc, metadata: metadata, ctx: txn});
      }
  
      txn.objectStore(DOC_STORE).get(id).onsuccess = function (e) {
        metadata = decodeMetadata(e.target.result);
        // we can determine the result here if:
        // 1. there is no such document
        // 2. the document is deleted and we don't ask about specific rev
        // When we ask with opts.rev we expect the answer to be either
        // doc (possibly with _deleted=true) or missing error
        if (!metadata) {
          err = createError(MISSING_DOC, 'missing');
          return finish();
        }
        if (isDeleted(metadata) && !opts.rev) {
          err = createError(MISSING_DOC, "deleted");
          return finish();
        }
        var objectStore = txn.objectStore(BY_SEQ_STORE);
  
        var rev = opts.rev || metadata.winningRev;
        var key = metadata.id + '::' + rev;
  
        objectStore.index('_doc_id_rev').get(key).onsuccess = function (e) {
          doc = e.target.result;
          if (doc) {
            doc = decodeDoc(doc);
          }
          if (!doc) {
            err = createError(MISSING_DOC, 'missing');
            return finish();
          }
          finish();
        };
      };
    };
  
    api._getAttachment = function (docId, attachId, attachment, opts, callback) {
      var txn;
      if (opts.ctx) {
        txn = opts.ctx;
      } else {
        var txnResult = openTransactionSafely(idb,
          [DOC_STORE, BY_SEQ_STORE, ATTACH_STORE], 'readonly');
        if (txnResult.error) {
          return callback(txnResult.error);
        }
        txn = txnResult.txn;
      }
      var digest = attachment.digest;
      var type = attachment.content_type;
  
      txn.objectStore(ATTACH_STORE).get(digest).onsuccess = function (e) {
        var body = e.target.result.body;
        readBlobData(body, type, opts.binary, function (blobData) {
          callback(null, blobData);
        });
      };
    };
  
    api._info = function idb_info(callback) {
  
      if (idb === null || !cachedDBs.has(dbName)) {
        var error = new Error('db isn\'t open');
        error.id = 'idbNull';
        return callback(error);
      }
      var updateSeq;
      var docCount;
  
      var txnResult = openTransactionSafely(idb, [BY_SEQ_STORE], 'readonly');
      if (txnResult.error) {
        return callback(txnResult.error);
      }
      var txn = txnResult.txn;
      var cursor = txn.objectStore(BY_SEQ_STORE).openCursor(null, 'prev');
      cursor.onsuccess = function (event) {
        var cursor = event.target.result;
        updateSeq = cursor ? cursor.key : 0;
        // count within the same txn for consistency
        docCount = api._meta.docCount;
      };
  
      txn.oncomplete = function () {
        callback(null, {
          doc_count: docCount,
          update_seq: updateSeq,
          // for debugging
          idb_attachment_format: (api._meta.blobSupport ? 'binary' : 'base64')
        });
      };
    };
  
    api._allDocs = function idb_allDocs(opts, callback) {
      idbAllDocs(opts, api, idb, callback);
    };
  
    api._changes = function (opts) {
      opts = clone(opts);
  
      if (opts.continuous) {
        var id = dbName + ':' + uuid();
        idbChanges.addListener(dbName, id, api, opts);
        idbChanges.notify(dbName);
        return {
          cancel: function () {
            idbChanges.removeListener(dbName, id);
          }
        };
      }
  
      var docIds = opts.doc_ids && new _Set(opts.doc_ids);
  
      opts.since = opts.since || 0;
      var lastSeq = opts.since;
  
      var limit = 'limit' in opts ? opts.limit : -1;
      if (limit === 0) {
        limit = 1; // per CouchDB _changes spec
      }
      var returnDocs;
      if ('return_docs' in opts) {
        returnDocs = opts.return_docs;
      } else if ('returnDocs' in opts) {
        // TODO: Remove 'returnDocs' in favor of 'return_docs' in a future release
        returnDocs = opts.returnDocs;
      } else {
        returnDocs = true;
      }
  
      var results = [];
      var numResults = 0;
      var filter = filterChange(opts);
      var docIdsToMetadata = new _Map();
  
      var txn;
      var bySeqStore;
      var docStore;
      var docIdRevIndex;
  
      function onGetCursor(cursor) {
  
        var doc = decodeDoc(cursor.value);
        var seq = cursor.key;
  
        if (docIds && !docIds.has(doc._id)) {
          return cursor["continue"]();
        }
  
        var metadata;
  
        function onGetMetadata() {
          if (metadata.seq !== seq) {
            // some other seq is later
            return cursor["continue"]();
          }
  
          lastSeq = seq;
  
          if (metadata.winningRev === doc._rev) {
            return onGetWinningDoc(doc);
          }
  
          fetchWinningDoc();
        }
  
        function fetchWinningDoc() {
          var docIdRev = doc._id + '::' + metadata.winningRev;
          var req = docIdRevIndex.get(docIdRev);
          req.onsuccess = function (e) {
            onGetWinningDoc(decodeDoc(e.target.result));
          };
        }
  
        function onGetWinningDoc(winningDoc) {
  
          var change = opts.processChange(winningDoc, metadata, opts);
          change.seq = metadata.seq;
  
          var filtered = filter(change);
          if (typeof filtered === 'object') {
            return opts.complete(filtered);
          }
  
          if (filtered) {
            numResults++;
            if (returnDocs) {
              results.push(change);
            }
            // process the attachment immediately
            // for the benefit of live listeners
            if (opts.attachments && opts.include_docs) {
              fetchAttachmentsIfNecessary(winningDoc, opts, txn, function () {
                postProcessAttachments([change], opts.binary).then(function () {
                  opts.onChange(change);
                });
              });
            } else {
              opts.onChange(change);
            }
          }
          if (numResults !== limit) {
            cursor["continue"]();
          }
        }
  
        metadata = docIdsToMetadata.get(doc._id);
        if (metadata) { // cached
          return onGetMetadata();
        }
        // metadata not cached, have to go fetch it
        docStore.get(doc._id).onsuccess = function (event) {
          metadata = decodeMetadata(event.target.result);
          docIdsToMetadata.set(doc._id, metadata);
          onGetMetadata();
        };
      }
  
      function onsuccess(event) {
        var cursor = event.target.result;
  
        if (!cursor) {
          return;
        }
        onGetCursor(cursor);
      }
  
      function fetchChanges() {
        var objectStores = [DOC_STORE, BY_SEQ_STORE];
        if (opts.attachments) {
          objectStores.push(ATTACH_STORE);
        }
        var txnResult = openTransactionSafely(idb, objectStores, 'readonly');
        if (txnResult.error) {
          return opts.complete(txnResult.error);
        }
        txn = txnResult.txn;
        txn.onabort = idbError(opts.complete);
        txn.oncomplete = onTxnComplete;
  
        bySeqStore = txn.objectStore(BY_SEQ_STORE);
        docStore = txn.objectStore(DOC_STORE);
        docIdRevIndex = bySeqStore.index('_doc_id_rev');
  
        var req;
  
        if (opts.descending) {
          req = bySeqStore.openCursor(null, 'prev');
        } else {
          req = bySeqStore.openCursor(IDBKeyRange.lowerBound(opts.since, true));
        }
  
        req.onsuccess = onsuccess;
      }
  
      fetchChanges();
  
      function onTxnComplete() {
  
        function finish() {
          opts.complete(null, {
            results: results,
            last_seq: lastSeq
          });
        }
  
        if (!opts.continuous && opts.attachments) {
          // cannot guarantee that postProcessing was already done,
          // so do it again
          postProcessAttachments(results).then(finish);
        } else {
          finish();
        }
      }
    };
  
    api._close = function (callback) {
      if (idb === null) {
        return callback(createError(NOT_OPEN));
      }
  
      // https://developer.mozilla.org/en-US/docs/IndexedDB/IDBDatabase#close
      // "Returns immediately and closes the connection in a separate thread..."
      idb.close();
      cachedDBs["delete"](dbName);
      idb = null;
      callback();
    };
  
    api._getRevisionTree = function (docId, callback) {
      var txnResult = openTransactionSafely(idb, [DOC_STORE], 'readonly');
      if (txnResult.error) {
        return callback(txnResult.error);
      }
      var txn = txnResult.txn;
      var req = txn.objectStore(DOC_STORE).get(docId);
      req.onsuccess = function (event) {
        var doc = decodeMetadata(event.target.result);
        if (!doc) {
          callback(createError(MISSING_DOC));
        } else {
          callback(null, doc.rev_tree);
        }
      };
    };
  
    // This function removes revisions of document docId
    // which are listed in revs and sets this document
    // revision to to rev_tree
    api._doCompaction = function (docId, revs, callback) {
      var stores = [
        DOC_STORE,
        BY_SEQ_STORE,
        ATTACH_STORE,
        ATTACH_AND_SEQ_STORE
      ];
      var txnResult = openTransactionSafely(idb, stores, 'readwrite');
      if (txnResult.error) {
        return callback(txnResult.error);
      }
      var txn = txnResult.txn;
  
      var docStore = txn.objectStore(DOC_STORE);
  
      docStore.get(docId).onsuccess = function (event) {
        var metadata = decodeMetadata(event.target.result);
        traverseRevTree(metadata.rev_tree, function (isLeaf, pos,
                                                           revHash, ctx, opts) {
          var rev = pos + '-' + revHash;
          if (revs.indexOf(rev) !== -1) {
            opts.status = 'missing';
          }
        });
        compactRevs(revs, docId, txn);
        var winningRev = metadata.winningRev;
        var deleted = metadata.deleted;
        txn.objectStore(DOC_STORE).put(
          encodeMetadata(metadata, winningRev, deleted));
      };
      txn.onabort = idbError(callback);
      txn.oncomplete = function () {
        callback();
      };
    };
  
  
    api._getLocal = function (id, callback) {
      var txnResult = openTransactionSafely(idb, [LOCAL_STORE], 'readonly');
      if (txnResult.error) {
        return callback(txnResult.error);
      }
      var tx = txnResult.txn;
      var req = tx.objectStore(LOCAL_STORE).get(id);
  
      req.onerror = idbError(callback);
      req.onsuccess = function (e) {
        var doc = e.target.result;
        if (!doc) {
          callback(createError(MISSING_DOC));
        } else {
          delete doc['_doc_id_rev']; // for backwards compat
          callback(null, doc);
        }
      };
    };
  
    api._putLocal = function (doc, opts, callback) {
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
      delete doc._revisions; // ignore this, trust the rev
      var oldRev = doc._rev;
      var id = doc._id;
      if (!oldRev) {
        doc._rev = '0-1';
      } else {
        doc._rev = '0-' + (parseInt(oldRev.split('-')[1], 10) + 1);
      }
  
      var tx = opts.ctx;
      var ret;
      if (!tx) {
        var txnResult = openTransactionSafely(idb, [LOCAL_STORE], 'readwrite');
        if (txnResult.error) {
          return callback(txnResult.error);
        }
        tx = txnResult.txn;
        tx.onerror = idbError(callback);
        tx.oncomplete = function () {
          if (ret) {
            callback(null, ret);
          }
        };
      }
  
      var oStore = tx.objectStore(LOCAL_STORE);
      var req;
      if (oldRev) {
        req = oStore.get(id);
        req.onsuccess = function (e) {
          var oldDoc = e.target.result;
          if (!oldDoc || oldDoc._rev !== oldRev) {
            callback(createError(REV_CONFLICT));
          } else { // update
            var req = oStore.put(doc);
            req.onsuccess = function () {
              ret = {ok: true, id: doc._id, rev: doc._rev};
              if (opts.ctx) { // return immediately
                callback(null, ret);
              }
            };
          }
        };
      } else { // new doc
        req = oStore.add(doc);
        req.onerror = function (e) {
          // constraint error, already exists
          callback(createError(REV_CONFLICT));
          e.preventDefault(); // avoid transaction abort
          e.stopPropagation(); // avoid transaction onerror
        };
        req.onsuccess = function () {
          ret = {ok: true, id: doc._id, rev: doc._rev};
          if (opts.ctx) { // return immediately
            callback(null, ret);
          }
        };
      }
    };
  
    api._removeLocal = function (doc, opts, callback) {
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
      var tx = opts.ctx;
      if (!tx) {
        var txnResult = openTransactionSafely(idb, [LOCAL_STORE], 'readwrite');
        if (txnResult.error) {
          return callback(txnResult.error);
        }
        tx = txnResult.txn;
        tx.oncomplete = function () {
          if (ret) {
            callback(null, ret);
          }
        };
      }
      var ret;
      var id = doc._id;
      var oStore = tx.objectStore(LOCAL_STORE);
      var req = oStore.get(id);
  
      req.onerror = idbError(callback);
      req.onsuccess = function (e) {
        var oldDoc = e.target.result;
        if (!oldDoc || oldDoc._rev !== doc._rev) {
          callback(createError(MISSING_DOC));
        } else {
          oStore["delete"](id);
          ret = {ok: true, id: id, rev: '0-0'};
          if (opts.ctx) { // return immediately
            callback(null, ret);
          }
        }
      };
    };
  
    api._destroy = function (opts, callback) {
      idbChanges.removeAllListeners(dbName);
  
      //Close open request for "dbName" database to fix ie delay.
      var openReq = openReqList.get(dbName);
      if (openReq && openReq.result) {
        openReq.result.close();
        cachedDBs["delete"](dbName);
      }
      var req = indexedDB.deleteDatabase(dbName);
  
      req.onsuccess = function () {
        //Remove open request from the list.
        openReqList["delete"](dbName);
        if (hasLocalStorage() && (dbName in localStorage)) {
          delete localStorage[dbName];
        }
        callback(null, { 'ok': true });
      };
  
      req.onerror = idbError(callback);
    };
  
    var cached = cachedDBs.get(dbName);
  
    if (cached) {
      idb = cached.idb;
      api._meta = cached.global;
      process.nextTick(function () {
        callback(null, api);
      });
      return;
    }
  
    var req;
    if (opts.storage) {
      req = tryStorageOption(dbName, opts.storage);
    } else {
      req = indexedDB.open(dbName, ADAPTER_VERSION);
    }
  
    openReqList.set(dbName, req);
  
    req.onupgradeneeded = function (e) {
      var db = e.target.result;
      if (e.oldVersion < 1) {
        return createSchema(db); // new db, initial schema
      }
      // do migrations
  
      var txn = e.currentTarget.transaction;
      // these migrations have to be done in this function, before
      // control is returned to the event loop, because IndexedDB
  
      if (e.oldVersion < 3) {
        createLocalStoreSchema(db); // v2 -> v3
      }
      if (e.oldVersion < 4) {
        addAttachAndSeqStore(db); // v3 -> v4
      }
  
      var migrations = [
        addDeletedOrLocalIndex, // v1 -> v2
        migrateLocalStore,      // v2 -> v3
        migrateAttsAndSeqs,     // v3 -> v4
        migrateMetadata         // v4 -> v5
      ];
  
      var i = e.oldVersion;
  
      function next() {
        var migration = migrations[i - 1];
        i++;
        if (migration) {
          migration(txn, next);
        }
      }
  
      next();
    };
  
    req.onsuccess = function (e) {
  
      idb = e.target.result;
  
      idb.onversionchange = function () {
        idb.close();
        cachedDBs["delete"](dbName);
      };
  
      idb.onabort = function (e) {
        guardedConsole('error', 'Database has a global failure', e.target.error);
        idb.close();
        cachedDBs["delete"](dbName);
      };
  
      var txn = idb.transaction([
        META_STORE,
        DETECT_BLOB_SUPPORT_STORE,
        DOC_STORE
      ], 'readwrite');
  
      var req = txn.objectStore(META_STORE).get(META_STORE);
  
      var blobSupport = null;
      var docCount = null;
      var instanceId = null;
  
      req.onsuccess = function (e) {
  
        var checkSetupComplete = function () {
          if (blobSupport === null || docCount === null ||
              instanceId === null) {
            return;
          } else {
            api._meta = {
              name: dbName,
              instanceId: instanceId,
              blobSupport: blobSupport,
              docCount: docCount
            };
  
            cachedDBs.set(dbName, {
              idb: idb,
              global: api._meta
            });
            callback(null, api);
          }
        };
  
        //
        // fetch/store the id
        //
  
        var meta = e.target.result || {id: META_STORE};
        if (dbName  + '_id' in meta) {
          instanceId = meta[dbName + '_id'];
          checkSetupComplete();
        } else {
          instanceId = uuid();
          meta[dbName + '_id'] = instanceId;
          txn.objectStore(META_STORE).put(meta).onsuccess = function () {
            checkSetupComplete();
          };
        }
  
        //
        // check blob support
        //
  
        if (!blobSupportPromise) {
          // make sure blob support is only checked once
          blobSupportPromise = checkBlobSupport(txn);
        }
  
        blobSupportPromise.then(function (val) {
          blobSupport = val;
          checkSetupComplete();
        });
  
        //
        // count docs
        //
  
        var index = txn.objectStore(DOC_STORE).index('deletedOrLocal');
        index.count(IDBKeyRange.only('0')).onsuccess = function (e) {
          docCount = e.target.result;
          checkSetupComplete();
        };
  
      };
    };
  
    req.onerror = function () {
      var msg = 'Failed to open indexedDB, are you in private browsing mode?';
      guardedConsole('error', msg);
      callback(createError(IDB_ERROR, msg));
    };
  }
  
  IdbPouch.valid = function () {
    // Issue #2533, we finally gave up on doing bug
    // detection instead of browser sniffing. Safari brought us
    // to our knees.
    var isSafari = typeof openDatabase !== 'undefined' &&
      /(Safari|iPhone|iPad|iPod)/.test(navigator.userAgent) &&
      !/Chrome/.test(navigator.userAgent) &&
      !/BlackBerry/.test(navigator.platform);
  
    // some outdated implementations of IDB that appear on Samsung
    // and HTC Android devices <4.4 are missing IDBKeyRange
    return !isSafari && typeof indexedDB !== 'undefined' &&
      typeof IDBKeyRange !== 'undefined';
  };
  
  function tryStorageOption(dbName, storage) {
    try { // option only available in Firefox 26+
      return indexedDB.open(dbName, {
        version: ADAPTER_VERSION,
        storage: storage
      });
    } catch(err) {
        return indexedDB.open(dbName, ADAPTER_VERSION);
    }
  }
  
  function IDBPouch (PouchDB) {
    PouchDB.adapter('idb', IdbPouch, true);
  }
  
  //
  // Parsing hex strings. Yeah.
  //
  // So basically we need this because of a bug in WebSQL:
  // https://code.google.com/p/chromium/issues/detail?id=422690
  // https://bugs.webkit.org/show_bug.cgi?id=137637
  //
  // UTF-8 and UTF-16 are provided as separate functions
  // for meager performance improvements
  //
  
  function decodeUtf8(str) {
    return decodeURIComponent(escape(str));
  }
  
  function hexToInt(charCode) {
    // '0'-'9' is 48-57
    // 'A'-'F' is 65-70
    // SQLite will only give us uppercase hex
    return charCode < 65 ? (charCode - 48) : (charCode - 55);
  }
  
  
  // Example:
  // pragma encoding=utf8;
  // select hex('A');
  // returns '41'
  function parseHexUtf8(str, start, end) {
    var result = '';
    while (start < end) {
      result += String.fromCharCode(
        (hexToInt(str.charCodeAt(start++)) << 4) |
          hexToInt(str.charCodeAt(start++)));
    }
    return result;
  }
  
  // Example:
  // pragma encoding=utf16;
  // select hex('A');
  // returns '4100'
  // notice that the 00 comes after the 41 (i.e. it's swizzled)
  function parseHexUtf16(str, start, end) {
    var result = '';
    while (start < end) {
      // UTF-16, so swizzle the bytes
      result += String.fromCharCode(
        (hexToInt(str.charCodeAt(start + 2)) << 12) |
          (hexToInt(str.charCodeAt(start + 3)) << 8) |
          (hexToInt(str.charCodeAt(start)) << 4) |
          hexToInt(str.charCodeAt(start + 1)));
      start += 4;
    }
    return result;
  }
  
  function parseHexString(str, encoding) {
    if (encoding === 'UTF-8') {
      return decodeUtf8(parseHexUtf8(str, 0, str.length));
    } else {
      return parseHexUtf16(str, 0, str.length);
    }
  }
  
  function quote(str) {
    return "'" + str + "'";
  }
  
  var ADAPTER_VERSION$1 = 7; // used to manage migrations
  
  // The object stores created for each database
  // DOC_STORE stores the document meta data, its revision history and state
  var DOC_STORE$1 = quote('document-store');
  // BY_SEQ_STORE stores a particular version of a document, keyed by its
  // sequence id
  var BY_SEQ_STORE$1 = quote('by-sequence');
  // Where we store attachments
  var ATTACH_STORE$1 = quote('attach-store');
  var LOCAL_STORE$1 = quote('local-store');
  var META_STORE$1 = quote('metadata-store');
  // where we store many-to-many relations between attachment
  // digests and seqs
  var ATTACH_AND_SEQ_STORE$1 = quote('attach-seq-store');
  
  // escapeBlob and unescapeBlob are workarounds for a websql bug:
  // https://code.google.com/p/chromium/issues/detail?id=422690
  // https://bugs.webkit.org/show_bug.cgi?id=137637
  // The goal is to never actually insert the \u0000 character
  // in the database.
  function escapeBlob(str) {
    return str
      .replace(/\u0002/g, '\u0002\u0002')
      .replace(/\u0001/g, '\u0001\u0002')
      .replace(/\u0000/g, '\u0001\u0001');
  }
  
  function unescapeBlob(str) {
    return str
      .replace(/\u0001\u0001/g, '\u0000')
      .replace(/\u0001\u0002/g, '\u0001')
      .replace(/\u0002\u0002/g, '\u0002');
  }
  
  function stringifyDoc(doc) {
    // don't bother storing the id/rev. it uses lots of space,
    // in persistent map/reduce especially
    delete doc._id;
    delete doc._rev;
    return JSON.stringify(doc);
  }
  
  function unstringifyDoc(doc, id, rev) {
    doc = JSON.parse(doc);
    doc._id = id;
    doc._rev = rev;
    return doc;
  }
  
  // question mark groups IN queries, e.g. 3 -> '(?,?,?)'
  function qMarks(num) {
    var s = '(';
    while (num--) {
      s += '?';
      if (num) {
        s += ',';
      }
    }
    return s + ')';
  }
  
  function select(selector, table, joiner, where, orderBy) {
    return 'SELECT ' + selector + ' FROM ' +
      (typeof table === 'string' ? table : table.join(' JOIN ')) +
      (joiner ? (' ON ' + joiner) : '') +
      (where ? (' WHERE ' +
      (typeof where === 'string' ? where : where.join(' AND '))) : '') +
      (orderBy ? (' ORDER BY ' + orderBy) : '');
  }
  
  function compactRevs$1(revs, docId, tx) {
  
    if (!revs.length) {
      return;
    }
  
    var numDone = 0;
    var seqs = [];
  
    function checkDone() {
      if (++numDone === revs.length) { // done
        deleteOrphans();
      }
    }
  
    function deleteOrphans() {
      // find orphaned attachment digests
  
      if (!seqs.length) {
        return;
      }
  
      var sql = 'SELECT DISTINCT digest AS digest FROM ' +
        ATTACH_AND_SEQ_STORE$1 + ' WHERE seq IN ' + qMarks(seqs.length);
  
      tx.executeSql(sql, seqs, function (tx, res) {
  
        var digestsToCheck = [];
        for (var i = 0; i < res.rows.length; i++) {
          digestsToCheck.push(res.rows.item(i).digest);
        }
        if (!digestsToCheck.length) {
          return;
        }
  
        var sql = 'DELETE FROM ' + ATTACH_AND_SEQ_STORE$1 +
          ' WHERE seq IN (' +
          seqs.map(function () { return '?'; }).join(',') +
          ')';
        tx.executeSql(sql, seqs, function (tx) {
  
          var sql = 'SELECT digest FROM ' + ATTACH_AND_SEQ_STORE$1 +
            ' WHERE digest IN (' +
            digestsToCheck.map(function () { return '?'; }).join(',') +
            ')';
          tx.executeSql(sql, digestsToCheck, function (tx, res) {
            var nonOrphanedDigests = new _Set();
            for (var i = 0; i < res.rows.length; i++) {
              nonOrphanedDigests.add(res.rows.item(i).digest);
            }
            digestsToCheck.forEach(function (digest) {
              if (nonOrphanedDigests.has(digest)) {
                return;
              }
              tx.executeSql(
                'DELETE FROM ' + ATTACH_AND_SEQ_STORE$1 + ' WHERE digest=?',
                [digest]);
              tx.executeSql(
                'DELETE FROM ' + ATTACH_STORE$1 + ' WHERE digest=?', [digest]);
            });
          });
        });
      });
    }
  
    // update by-seq and attach stores in parallel
    revs.forEach(function (rev) {
      var sql = 'SELECT seq FROM ' + BY_SEQ_STORE$1 +
        ' WHERE doc_id=? AND rev=?';
  
      tx.executeSql(sql, [docId, rev], function (tx, res) {
        if (!res.rows.length) { // already deleted
          return checkDone();
        }
        var seq = res.rows.item(0).seq;
        seqs.push(seq);
  
        tx.executeSql(
          'DELETE FROM ' + BY_SEQ_STORE$1 + ' WHERE seq=?', [seq], checkDone);
      });
    });
  }
  
  function websqlError(callback) {
    return function (event) {
      guardedConsole('error', 'WebSQL threw an error', event);
      // event may actually be a SQLError object, so report is as such
      var errorNameMatch = event && event.constructor.toString()
          .match(/function ([^\(]+)/);
      var errorName = (errorNameMatch && errorNameMatch[1]) || event.type;
      var errorReason = event.target || event.message;
      callback(createError(WSQ_ERROR, errorReason, errorName));
    };
  }
  
  function getSize(opts) {
    if ('size' in opts) {
      // triggers immediate popup in iOS, fixes #2347
      // e.g. 5000001 asks for 5 MB, 10000001 asks for 10 MB,
      return opts.size * 1000000;
    }
    // In iOS, doesn't matter as long as it's <= 5000000.
    // Except that if you request too much, our tests fail
    // because of the native "do you accept?" popup.
    // In Android <=4.3, this value is actually used as an
    // honest-to-god ceiling for data, so we need to
    // set it to a decently high number.
    var isAndroid = typeof navigator !== 'undefined' &&
      /Android/.test(navigator.userAgent);
    return isAndroid ? 5000000 : 1; // in PhantomJS, if you use 0 it will crash
  }
  
  function websqlBulkDocs(dbOpts, req, opts, api, db, websqlChanges, callback) {
    var newEdits = opts.new_edits;
    var userDocs = req.docs;
  
    // Parse the docs, give them a sequence number for the result
    var docInfos = userDocs.map(function (doc) {
      if (doc._id && isLocalId(doc._id)) {
        return doc;
      }
      var newDoc = parseDoc(doc, newEdits);
      return newDoc;
    });
  
    var docInfoErrors = docInfos.filter(function (docInfo) {
      return docInfo.error;
    });
    if (docInfoErrors.length) {
      return callback(docInfoErrors[0]);
    }
  
    var tx;
    var results = new Array(docInfos.length);
    var fetchedDocs = new _Map();
  
    var preconditionErrored;
    function complete() {
      if (preconditionErrored) {
        return callback(preconditionErrored);
      }
      websqlChanges.notify(api._name);
      api._docCount = -1; // invalidate
      callback(null, results);
    }
  
    function verifyAttachment(digest, callback) {
      var sql = 'SELECT count(*) as cnt FROM ' + ATTACH_STORE$1 +
        ' WHERE digest=?';
      tx.executeSql(sql, [digest], function (tx, result) {
        if (result.rows.item(0).cnt === 0) {
          var err = createError(MISSING_STUB,
            'unknown stub attachment with digest ' +
            digest);
          callback(err);
        } else {
          callback();
        }
      });
    }
  
    function verifyAttachments(finish) {
      var digests = [];
      docInfos.forEach(function (docInfo) {
        if (docInfo.data && docInfo.data._attachments) {
          Object.keys(docInfo.data._attachments).forEach(function (filename) {
            var att = docInfo.data._attachments[filename];
            if (att.stub) {
              digests.push(att.digest);
            }
          });
        }
      });
      if (!digests.length) {
        return finish();
      }
      var numDone = 0;
      var err;
  
      function checkDone() {
        if (++numDone === digests.length) {
          finish(err);
        }
      }
      digests.forEach(function (digest) {
        verifyAttachment(digest, function (attErr) {
          if (attErr && !err) {
            err = attErr;
          }
          checkDone();
        });
      });
    }
  
    function writeDoc(docInfo, winningRev, winningRevIsDeleted, newRevIsDeleted,
                      isUpdate, delta, resultsIdx, callback) {
  
      function finish() {
        var data = docInfo.data;
        var deletedInt = newRevIsDeleted ? 1 : 0;
  
        var id = data._id;
        var rev = data._rev;
        var json = stringifyDoc(data);
        var sql = 'INSERT INTO ' + BY_SEQ_STORE$1 +
          ' (doc_id, rev, json, deleted) VALUES (?, ?, ?, ?);';
        var sqlArgs = [id, rev, json, deletedInt];
  
        // map seqs to attachment digests, which
        // we will need later during compaction
        function insertAttachmentMappings(seq, callback) {
          var attsAdded = 0;
          var attsToAdd = Object.keys(data._attachments || {});
  
          if (!attsToAdd.length) {
            return callback();
          }
          function checkDone() {
            if (++attsAdded === attsToAdd.length) {
              callback();
            }
            return false; // ack handling a constraint error
          }
          function add(att) {
            var sql = 'INSERT INTO ' + ATTACH_AND_SEQ_STORE$1 +
              ' (digest, seq) VALUES (?,?)';
            var sqlArgs = [data._attachments[att].digest, seq];
            tx.executeSql(sql, sqlArgs, checkDone, checkDone);
            // second callback is for a constaint error, which we ignore
            // because this docid/rev has already been associated with
            // the digest (e.g. when new_edits == false)
          }
          for (var i = 0; i < attsToAdd.length; i++) {
            add(attsToAdd[i]); // do in parallel
          }
        }
  
        tx.executeSql(sql, sqlArgs, function (tx, result) {
          var seq = result.insertId;
          insertAttachmentMappings(seq, function () {
            dataWritten(tx, seq);
          });
        }, function () {
          // constraint error, recover by updating instead (see #1638)
          var fetchSql = select('seq', BY_SEQ_STORE$1, null,
            'doc_id=? AND rev=?');
          tx.executeSql(fetchSql, [id, rev], function (tx, res) {
            var seq = res.rows.item(0).seq;
            var sql = 'UPDATE ' + BY_SEQ_STORE$1 +
              ' SET json=?, deleted=? WHERE doc_id=? AND rev=?;';
            var sqlArgs = [json, deletedInt, id, rev];
            tx.executeSql(sql, sqlArgs, function (tx) {
              insertAttachmentMappings(seq, function () {
                dataWritten(tx, seq);
              });
            });
          });
          return false; // ack that we've handled the error
        });
      }
  
      function collectResults(attachmentErr) {
        if (!err) {
          if (attachmentErr) {
            err = attachmentErr;
            callback(err);
          } else if (recv === attachments.length) {
            finish();
          }
        }
      }
  
      var err = null;
      var recv = 0;
  
      docInfo.data._id = docInfo.metadata.id;
      docInfo.data._rev = docInfo.metadata.rev;
      var attachments = Object.keys(docInfo.data._attachments || {});
  
  
      if (newRevIsDeleted) {
        docInfo.data._deleted = true;
      }
  
      function attachmentSaved(err) {
        recv++;
        collectResults(err);
      }
  
      attachments.forEach(function (key) {
        var att = docInfo.data._attachments[key];
        if (!att.stub) {
          var data = att.data;
          delete att.data;
          att.revpos = parseInt(winningRev, 10);
          var digest = att.digest;
          saveAttachment(digest, data, attachmentSaved);
        } else {
          recv++;
          collectResults();
        }
      });
  
      if (!attachments.length) {
        finish();
      }
  
      function dataWritten(tx, seq) {
        var id = docInfo.metadata.id;
  
        var revsToCompact = docInfo.stemmedRevs || [];
        if (isUpdate && api.auto_compaction) {
          revsToCompact = compactTree(docInfo.metadata).concat(revsToCompact);
        }
        if (revsToCompact.length) {
          compactRevs$1(revsToCompact, id, tx);
        }
  
        docInfo.metadata.seq = seq;
        delete docInfo.metadata.rev;
  
        var sql = isUpdate ?
        'UPDATE ' + DOC_STORE$1 +
        ' SET json=?, max_seq=?, winningseq=' +
        '(SELECT seq FROM ' + BY_SEQ_STORE$1 +
        ' WHERE doc_id=' + DOC_STORE$1 + '.id AND rev=?) WHERE id=?'
          : 'INSERT INTO ' + DOC_STORE$1 +
        ' (id, winningseq, max_seq, json) VALUES (?,?,?,?);';
        var metadataStr = safeJsonStringify(docInfo.metadata);
        var params = isUpdate ?
          [metadataStr, seq, winningRev, id] :
          [id, seq, seq, metadataStr];
        tx.executeSql(sql, params, function () {
          results[resultsIdx] = {
            ok: true,
            id: docInfo.metadata.id,
            rev: winningRev
          };
          fetchedDocs.set(id, docInfo.metadata);
          callback();
        });
      }
    }
  
    function websqlProcessDocs() {
      processDocs(dbOpts.revs_limit, docInfos, api, fetchedDocs, tx,
                  results, writeDoc, opts);
    }
  
    function fetchExistingDocs(callback) {
      if (!docInfos.length) {
        return callback();
      }
  
      var numFetched = 0;
  
      function checkDone() {
        if (++numFetched === docInfos.length) {
          callback();
        }
      }
  
      docInfos.forEach(function (docInfo) {
        if (docInfo._id && isLocalId(docInfo._id)) {
          return checkDone(); // skip local docs
        }
        var id = docInfo.metadata.id;
        tx.executeSql('SELECT json FROM ' + DOC_STORE$1 +
        ' WHERE id = ?', [id], function (tx, result) {
          if (result.rows.length) {
            var metadata = safeJsonParse(result.rows.item(0).json);
            fetchedDocs.set(id, metadata);
          }
          checkDone();
        });
      });
    }
  
    function saveAttachment(digest, data, callback) {
      var sql = 'SELECT digest FROM ' + ATTACH_STORE$1 + ' WHERE digest=?';
      tx.executeSql(sql, [digest], function (tx, result) {
        if (result.rows.length) { // attachment already exists
          return callback();
        }
        // we could just insert before selecting and catch the error,
        // but my hunch is that it's cheaper not to serialize the blob
        // from JS to C if we don't have to (TODO: confirm this)
        sql = 'INSERT INTO ' + ATTACH_STORE$1 +
        ' (digest, body, escaped) VALUES (?,?,1)';
        tx.executeSql(sql, [digest, escapeBlob(data)], function () {
          callback();
        }, function () {
          // ignore constaint errors, means it already exists
          callback();
          return false; // ack we handled the error
        });
      });
    }
  
    preprocessAttachments(docInfos, 'binary', function (err) {
      if (err) {
        return callback(err);
      }
      db.transaction(function (txn) {
        tx = txn;
        verifyAttachments(function (err) {
          if (err) {
            preconditionErrored = err;
          } else {
            fetchExistingDocs(websqlProcessDocs);
          }
        });
      }, websqlError(callback), complete);
    });
  }
  
  var cachedDatabases = new _Map();
  
  // openDatabase passed in through opts (e.g. for node-websql)
  function openDatabaseWithOpts(opts) {
    return opts.websql(opts.name, opts.version, opts.description, opts.size);
  }
  
  function openDBSafely(opts) {
    try {
      return {
        db: openDatabaseWithOpts(opts)
      };
    } catch (err) {
      return {
        error: err
      };
    }
  }
  
  function openDB$1(opts) {
    var cachedResult = cachedDatabases.get(opts.name);
    if (!cachedResult) {
      cachedResult = openDBSafely(opts);
      cachedDatabases.set(opts.name, cachedResult);
    }
    return cachedResult;
  }
  
  var websqlChanges = new Changes$1();
  
  function fetchAttachmentsIfNecessary$1(doc, opts, api, txn, cb) {
    var attachments = Object.keys(doc._attachments || {});
    if (!attachments.length) {
      return cb && cb();
    }
    var numDone = 0;
  
    function checkDone() {
      if (++numDone === attachments.length && cb) {
        cb();
      }
    }
  
    function fetchAttachment(doc, att) {
      var attObj = doc._attachments[att];
      var attOpts = {binary: opts.binary, ctx: txn};
      api._getAttachment(doc._id, att, attObj, attOpts, function (_, data) {
        doc._attachments[att] = jsExtend.extend(
          pick(attObj, ['digest', 'content_type']),
          { data: data }
        );
        checkDone();
      });
    }
  
    attachments.forEach(function (att) {
      if (opts.attachments && opts.include_docs) {
        fetchAttachment(doc, att);
      } else {
        doc._attachments[att].stub = true;
        checkDone();
      }
    });
  }
  
  var POUCH_VERSION = 1;
  
  // these indexes cover the ground for most allDocs queries
  var BY_SEQ_STORE_DELETED_INDEX_SQL =
    'CREATE INDEX IF NOT EXISTS \'by-seq-deleted-idx\' ON ' +
    BY_SEQ_STORE$1 + ' (seq, deleted)';
  var BY_SEQ_STORE_DOC_ID_REV_INDEX_SQL =
    'CREATE UNIQUE INDEX IF NOT EXISTS \'by-seq-doc-id-rev\' ON ' +
      BY_SEQ_STORE$1 + ' (doc_id, rev)';
  var DOC_STORE_WINNINGSEQ_INDEX_SQL =
    'CREATE INDEX IF NOT EXISTS \'doc-winningseq-idx\' ON ' +
    DOC_STORE$1 + ' (winningseq)';
  var ATTACH_AND_SEQ_STORE_SEQ_INDEX_SQL =
    'CREATE INDEX IF NOT EXISTS \'attach-seq-seq-idx\' ON ' +
      ATTACH_AND_SEQ_STORE$1 + ' (seq)';
  var ATTACH_AND_SEQ_STORE_ATTACH_INDEX_SQL =
    'CREATE UNIQUE INDEX IF NOT EXISTS \'attach-seq-digest-idx\' ON ' +
      ATTACH_AND_SEQ_STORE$1 + ' (digest, seq)';
  
  var DOC_STORE_AND_BY_SEQ_JOINER = BY_SEQ_STORE$1 +
    '.seq = ' + DOC_STORE$1 + '.winningseq';
  
  var SELECT_DOCS = BY_SEQ_STORE$1 + '.seq AS seq, ' +
    BY_SEQ_STORE$1 + '.deleted AS deleted, ' +
    BY_SEQ_STORE$1 + '.json AS data, ' +
    BY_SEQ_STORE$1 + '.rev AS rev, ' +
    DOC_STORE$1 + '.json AS metadata';
  
  function WebSqlPouch$1(opts, callback) {
    var api = this;
    var instanceId = null;
    var size = getSize(opts);
    var idRequests = [];
    var encoding;
  
    api._docCount = -1; // cache sqlite count(*) for performance
    api._name = opts.name;
  
    // extend the options here, because sqlite plugin has a ton of options
    // and they are constantly changing, so it's more prudent to allow anything
    var websqlOpts = jsExtend.extend({}, opts, {
      version: POUCH_VERSION,
      description: opts.name,
      size: size
    });
    var openDBResult = openDB$1(websqlOpts);
    if (openDBResult.error) {
      return websqlError(callback)(openDBResult.error);
    }
    var db = openDBResult.db;
    if (typeof db.readTransaction !== 'function') {
      // doesn't exist in sqlite plugin
      db.readTransaction = db.transaction;
    }
  
    function dbCreated() {
      // note the db name in case the browser upgrades to idb
      if (hasLocalStorage()) {
        window.localStorage['_pouch__websqldb_' + api._name] = true;
      }
      callback(null, api);
    }
  
    // In this migration, we added the 'deleted' and 'local' columns to the
    // by-seq and doc store tables.
    // To preserve existing user data, we re-process all the existing JSON
    // and add these values.
    // Called migration2 because it corresponds to adapter version (db_version) #2
    function runMigration2(tx, callback) {
      // index used for the join in the allDocs query
      tx.executeSql(DOC_STORE_WINNINGSEQ_INDEX_SQL);
  
      tx.executeSql('ALTER TABLE ' + BY_SEQ_STORE$1 +
        ' ADD COLUMN deleted TINYINT(1) DEFAULT 0', [], function () {
        tx.executeSql(BY_SEQ_STORE_DELETED_INDEX_SQL);
        tx.executeSql('ALTER TABLE ' + DOC_STORE$1 +
          ' ADD COLUMN local TINYINT(1) DEFAULT 0', [], function () {
          tx.executeSql('CREATE INDEX IF NOT EXISTS \'doc-store-local-idx\' ON ' +
            DOC_STORE$1 + ' (local, id)');
  
          var sql = 'SELECT ' + DOC_STORE$1 + '.winningseq AS seq, ' + DOC_STORE$1 +
            '.json AS metadata FROM ' + BY_SEQ_STORE$1 + ' JOIN ' + DOC_STORE$1 +
            ' ON ' + BY_SEQ_STORE$1 + '.seq = ' + DOC_STORE$1 + '.winningseq';
  
          tx.executeSql(sql, [], function (tx, result) {
  
            var deleted = [];
            var local = [];
  
            for (var i = 0; i < result.rows.length; i++) {
              var item = result.rows.item(i);
              var seq = item.seq;
              var metadata = JSON.parse(item.metadata);
              if (isDeleted(metadata)) {
                deleted.push(seq);
              }
              if (isLocalId(metadata.id)) {
                local.push(metadata.id);
              }
            }
            tx.executeSql('UPDATE ' + DOC_STORE$1 + 'SET local = 1 WHERE id IN ' +
              qMarks(local.length), local, function () {
              tx.executeSql('UPDATE ' + BY_SEQ_STORE$1 +
                ' SET deleted = 1 WHERE seq IN ' +
                qMarks(deleted.length), deleted, callback);
            });
          });
        });
      });
    }
  
    // in this migration, we make all the local docs unversioned
    function runMigration3(tx, callback) {
      var local = 'CREATE TABLE IF NOT EXISTS ' + LOCAL_STORE$1 +
        ' (id UNIQUE, rev, json)';
      tx.executeSql(local, [], function () {
        var sql = 'SELECT ' + DOC_STORE$1 + '.id AS id, ' +
          BY_SEQ_STORE$1 + '.json AS data ' +
          'FROM ' + BY_SEQ_STORE$1 + ' JOIN ' +
          DOC_STORE$1 + ' ON ' + BY_SEQ_STORE$1 + '.seq = ' +
          DOC_STORE$1 + '.winningseq WHERE local = 1';
        tx.executeSql(sql, [], function (tx, res) {
          var rows = [];
          for (var i = 0; i < res.rows.length; i++) {
            rows.push(res.rows.item(i));
          }
          function doNext() {
            if (!rows.length) {
              return callback(tx);
            }
            var row = rows.shift();
            var rev = JSON.parse(row.data)._rev;
            tx.executeSql('INSERT INTO ' + LOCAL_STORE$1 +
                ' (id, rev, json) VALUES (?,?,?)',
                [row.id, rev, row.data], function (tx) {
              tx.executeSql('DELETE FROM ' + DOC_STORE$1 + ' WHERE id=?',
                  [row.id], function (tx) {
                tx.executeSql('DELETE FROM ' + BY_SEQ_STORE$1 + ' WHERE seq=?',
                    [row.seq], function () {
                  doNext();
                });
              });
            });
          }
          doNext();
        });
      });
    }
  
    // in this migration, we remove doc_id_rev and just use rev
    function runMigration4(tx, callback) {
  
      function updateRows(rows) {
        function doNext() {
          if (!rows.length) {
            return callback(tx);
          }
          var row = rows.shift();
          var doc_id_rev = parseHexString(row.hex, encoding);
          var idx = doc_id_rev.lastIndexOf('::');
          var doc_id = doc_id_rev.substring(0, idx);
          var rev = doc_id_rev.substring(idx + 2);
          var sql = 'UPDATE ' + BY_SEQ_STORE$1 +
            ' SET doc_id=?, rev=? WHERE doc_id_rev=?';
          tx.executeSql(sql, [doc_id, rev, doc_id_rev], function () {
            doNext();
          });
        }
        doNext();
      }
  
      var sql = 'ALTER TABLE ' + BY_SEQ_STORE$1 + ' ADD COLUMN doc_id';
      tx.executeSql(sql, [], function (tx) {
        var sql = 'ALTER TABLE ' + BY_SEQ_STORE$1 + ' ADD COLUMN rev';
        tx.executeSql(sql, [], function (tx) {
          tx.executeSql(BY_SEQ_STORE_DOC_ID_REV_INDEX_SQL, [], function (tx) {
            var sql = 'SELECT hex(doc_id_rev) as hex FROM ' + BY_SEQ_STORE$1;
            tx.executeSql(sql, [], function (tx, res) {
              var rows = [];
              for (var i = 0; i < res.rows.length; i++) {
                rows.push(res.rows.item(i));
              }
              updateRows(rows);
            });
          });
        });
      });
    }
  
    // in this migration, we add the attach_and_seq table
    // for issue #2818
    function runMigration5(tx, callback) {
  
      function migrateAttsAndSeqs(tx) {
        // need to actually populate the table. this is the expensive part,
        // so as an optimization, check first that this database even
        // contains attachments
        var sql = 'SELECT COUNT(*) AS cnt FROM ' + ATTACH_STORE$1;
        tx.executeSql(sql, [], function (tx, res) {
          var count = res.rows.item(0).cnt;
          if (!count) {
            return callback(tx);
          }
  
          var offset = 0;
          var pageSize = 10;
          function nextPage() {
            var sql = select(
              SELECT_DOCS + ', ' + DOC_STORE$1 + '.id AS id',
              [DOC_STORE$1, BY_SEQ_STORE$1],
              DOC_STORE_AND_BY_SEQ_JOINER,
              null,
              DOC_STORE$1 + '.id '
            );
            sql += ' LIMIT ' + pageSize + ' OFFSET ' + offset;
            offset += pageSize;
            tx.executeSql(sql, [], function (tx, res) {
              if (!res.rows.length) {
                return callback(tx);
              }
              var digestSeqs = {};
              function addDigestSeq(digest, seq) {
                // uniq digest/seq pairs, just in case there are dups
                var seqs = digestSeqs[digest] = (digestSeqs[digest] || []);
                if (seqs.indexOf(seq) === -1) {
                  seqs.push(seq);
                }
              }
              for (var i = 0; i < res.rows.length; i++) {
                var row = res.rows.item(i);
                var doc = unstringifyDoc(row.data, row.id, row.rev);
                var atts = Object.keys(doc._attachments || {});
                for (var j = 0; j < atts.length; j++) {
                  var att = doc._attachments[atts[j]];
                  addDigestSeq(att.digest, row.seq);
                }
              }
              var digestSeqPairs = [];
              Object.keys(digestSeqs).forEach(function (digest) {
                var seqs = digestSeqs[digest];
                seqs.forEach(function (seq) {
                  digestSeqPairs.push([digest, seq]);
                });
              });
              if (!digestSeqPairs.length) {
                return nextPage();
              }
              var numDone = 0;
              digestSeqPairs.forEach(function (pair) {
                var sql = 'INSERT INTO ' + ATTACH_AND_SEQ_STORE$1 +
                  ' (digest, seq) VALUES (?,?)';
                tx.executeSql(sql, pair, function () {
                  if (++numDone === digestSeqPairs.length) {
                    nextPage();
                  }
                });
              });
            });
          }
          nextPage();
        });
      }
  
      var attachAndRev = 'CREATE TABLE IF NOT EXISTS ' +
        ATTACH_AND_SEQ_STORE$1 + ' (digest, seq INTEGER)';
      tx.executeSql(attachAndRev, [], function (tx) {
        tx.executeSql(
          ATTACH_AND_SEQ_STORE_ATTACH_INDEX_SQL, [], function (tx) {
            tx.executeSql(
              ATTACH_AND_SEQ_STORE_SEQ_INDEX_SQL, [],
              migrateAttsAndSeqs);
          });
      });
    }
  
    // in this migration, we use escapeBlob() and unescapeBlob()
    // instead of reading out the binary as HEX, which is slow
    function runMigration6(tx, callback) {
      var sql = 'ALTER TABLE ' + ATTACH_STORE$1 +
        ' ADD COLUMN escaped TINYINT(1) DEFAULT 0';
      tx.executeSql(sql, [], callback);
    }
  
    // issue #3136, in this migration we need a "latest seq" as well
    // as the "winning seq" in the doc store
    function runMigration7(tx, callback) {
      var sql = 'ALTER TABLE ' + DOC_STORE$1 +
        ' ADD COLUMN max_seq INTEGER';
      tx.executeSql(sql, [], function (tx) {
        var sql = 'UPDATE ' + DOC_STORE$1 + ' SET max_seq=(SELECT MAX(seq) FROM ' +
          BY_SEQ_STORE$1 + ' WHERE doc_id=id)';
        tx.executeSql(sql, [], function (tx) {
          // add unique index after filling, else we'll get a constraint
          // error when we do the ALTER TABLE
          var sql =
            'CREATE UNIQUE INDEX IF NOT EXISTS \'doc-max-seq-idx\' ON ' +
            DOC_STORE$1 + ' (max_seq)';
          tx.executeSql(sql, [], callback);
        });
      });
    }
  
    function checkEncoding(tx, cb) {
      // UTF-8 on chrome/android, UTF-16 on safari < 7.1
      tx.executeSql('SELECT HEX("a") AS hex', [], function (tx, res) {
          var hex = res.rows.item(0).hex;
          encoding = hex.length === 2 ? 'UTF-8' : 'UTF-16';
          cb();
        }
      );
    }
  
    function onGetInstanceId() {
      while (idRequests.length > 0) {
        var idCallback = idRequests.pop();
        idCallback(null, instanceId);
      }
    }
  
    function onGetVersion(tx, dbVersion) {
      if (dbVersion === 0) {
        // initial schema
  
        var meta = 'CREATE TABLE IF NOT EXISTS ' + META_STORE$1 +
          ' (dbid, db_version INTEGER)';
        var attach = 'CREATE TABLE IF NOT EXISTS ' + ATTACH_STORE$1 +
          ' (digest UNIQUE, escaped TINYINT(1), body BLOB)';
        var attachAndRev = 'CREATE TABLE IF NOT EXISTS ' +
          ATTACH_AND_SEQ_STORE$1 + ' (digest, seq INTEGER)';
        // TODO: migrate winningseq to INTEGER
        var doc = 'CREATE TABLE IF NOT EXISTS ' + DOC_STORE$1 +
          ' (id unique, json, winningseq, max_seq INTEGER UNIQUE)';
        var seq = 'CREATE TABLE IF NOT EXISTS ' + BY_SEQ_STORE$1 +
          ' (seq INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, ' +
          'json, deleted TINYINT(1), doc_id, rev)';
        var local = 'CREATE TABLE IF NOT EXISTS ' + LOCAL_STORE$1 +
          ' (id UNIQUE, rev, json)';
  
        // creates
        tx.executeSql(attach);
        tx.executeSql(local);
        tx.executeSql(attachAndRev, [], function () {
          tx.executeSql(ATTACH_AND_SEQ_STORE_SEQ_INDEX_SQL);
          tx.executeSql(ATTACH_AND_SEQ_STORE_ATTACH_INDEX_SQL);
        });
        tx.executeSql(doc, [], function () {
          tx.executeSql(DOC_STORE_WINNINGSEQ_INDEX_SQL);
          tx.executeSql(seq, [], function () {
            tx.executeSql(BY_SEQ_STORE_DELETED_INDEX_SQL);
            tx.executeSql(BY_SEQ_STORE_DOC_ID_REV_INDEX_SQL);
            tx.executeSql(meta, [], function () {
              // mark the db version, and new dbid
              var initSeq = 'INSERT INTO ' + META_STORE$1 +
                ' (db_version, dbid) VALUES (?,?)';
              instanceId = uuid();
              var initSeqArgs = [ADAPTER_VERSION$1, instanceId];
              tx.executeSql(initSeq, initSeqArgs, function () {
                onGetInstanceId();
              });
            });
          });
        });
      } else { // version > 0
  
        var setupDone = function () {
          var migrated = dbVersion < ADAPTER_VERSION$1;
          if (migrated) {
            // update the db version within this transaction
            tx.executeSql('UPDATE ' + META_STORE$1 + ' SET db_version = ' +
              ADAPTER_VERSION$1);
          }
          // notify db.id() callers
          var sql = 'SELECT dbid FROM ' + META_STORE$1;
          tx.executeSql(sql, [], function (tx, result) {
            instanceId = result.rows.item(0).dbid;
            onGetInstanceId();
          });
        };
  
        // would love to use promises here, but then websql
        // ends the transaction early
        var tasks = [
          runMigration2,
          runMigration3,
          runMigration4,
          runMigration5,
          runMigration6,
          runMigration7,
          setupDone
        ];
  
        // run each migration sequentially
        var i = dbVersion;
        var nextMigration = function (tx) {
          tasks[i - 1](tx, nextMigration);
          i++;
        };
        nextMigration(tx);
      }
    }
  
    function setup() {
      db.transaction(function (tx) {
        // first check the encoding
        checkEncoding(tx, function () {
          // then get the version
          fetchVersion(tx);
        });
      }, websqlError(callback), dbCreated);
    }
  
    function fetchVersion(tx) {
      var sql = 'SELECT sql FROM sqlite_master WHERE tbl_name = ' + META_STORE$1;
      tx.executeSql(sql, [], function (tx, result) {
        if (!result.rows.length) {
          // database hasn't even been created yet (version 0)
          onGetVersion(tx, 0);
        } else if (!/db_version/.test(result.rows.item(0).sql)) {
          // table was created, but without the new db_version column,
          // so add it.
          tx.executeSql('ALTER TABLE ' + META_STORE$1 +
            ' ADD COLUMN db_version INTEGER', [], function () {
            // before version 2, this column didn't even exist
            onGetVersion(tx, 1);
          });
        } else { // column exists, we can safely get it
          tx.executeSql('SELECT db_version FROM ' + META_STORE$1,
            [], function (tx, result) {
            var dbVersion = result.rows.item(0).db_version;
            onGetVersion(tx, dbVersion);
          });
        }
      });
    }
  
    setup();
  
    api.type = function () {
      return 'websql';
    };
  
    api._id = toPromise(function (callback) {
      callback(null, instanceId);
    });
  
    api._info = function (callback) {
      db.readTransaction(function (tx) {
        countDocs(tx, function (docCount) {
          var sql = 'SELECT MAX(seq) AS seq FROM ' + BY_SEQ_STORE$1;
          tx.executeSql(sql, [], function (tx, res) {
            var updateSeq = res.rows.item(0).seq || 0;
            callback(null, {
              doc_count: docCount,
              update_seq: updateSeq,
              websql_encoding: encoding
            });
          });
        });
      }, websqlError(callback));
    };
  
    api._bulkDocs = function (req, reqOpts, callback) {
      websqlBulkDocs(opts, req, reqOpts, api, db, websqlChanges, callback);
    };
  
    api._get = function (id, opts, callback) {
      var doc;
      var metadata;
      var err;
      var tx = opts.ctx;
      if (!tx) {
        return db.readTransaction(function (txn) {
          api._get(id, jsExtend.extend({ctx: txn}, opts), callback);
        });
      }
  
      function finish() {
        callback(err, {doc: doc, metadata: metadata, ctx: tx});
      }
  
      var sql;
      var sqlArgs;
      if (opts.rev) {
        sql = select(
          SELECT_DOCS,
          [DOC_STORE$1, BY_SEQ_STORE$1],
          DOC_STORE$1 + '.id=' + BY_SEQ_STORE$1 + '.doc_id',
          [BY_SEQ_STORE$1 + '.doc_id=?', BY_SEQ_STORE$1 + '.rev=?']);
        sqlArgs = [id, opts.rev];
      } else {
        sql = select(
          SELECT_DOCS,
          [DOC_STORE$1, BY_SEQ_STORE$1],
          DOC_STORE_AND_BY_SEQ_JOINER,
          DOC_STORE$1 + '.id=?');
        sqlArgs = [id];
      }
      tx.executeSql(sql, sqlArgs, function (a, results) {
        if (!results.rows.length) {
          err = createError(MISSING_DOC, 'missing');
          return finish();
        }
        var item = results.rows.item(0);
        metadata = safeJsonParse(item.metadata);
        if (item.deleted && !opts.rev) {
          err = createError(MISSING_DOC, 'deleted');
          return finish();
        }
        doc = unstringifyDoc(item.data, metadata.id, item.rev);
        finish();
      });
    };
  
    function countDocs(tx, callback) {
  
      if (api._docCount !== -1) {
        return callback(api._docCount);
      }
  
      // count the total rows
      var sql = select(
        'COUNT(' + DOC_STORE$1 + '.id) AS \'num\'',
        [DOC_STORE$1, BY_SEQ_STORE$1],
        DOC_STORE_AND_BY_SEQ_JOINER,
        BY_SEQ_STORE$1 + '.deleted=0');
  
      tx.executeSql(sql, [], function (tx, result) {
        api._docCount = result.rows.item(0).num;
        callback(api._docCount);
      });
    }
  
    api._allDocs = function (opts, callback) {
      var results = [];
      var totalRows;
  
      var start = 'startkey' in opts ? opts.startkey : false;
      var end = 'endkey' in opts ? opts.endkey : false;
      var key = 'key' in opts ? opts.key : false;
      var descending = 'descending' in opts ? opts.descending : false;
      var limit = 'limit' in opts ? opts.limit : -1;
      var offset = 'skip' in opts ? opts.skip : 0;
      var inclusiveEnd = opts.inclusive_end !== false;
  
      var sqlArgs = [];
      var criteria = [];
  
      if (key !== false) {
        criteria.push(DOC_STORE$1 + '.id = ?');
        sqlArgs.push(key);
      } else if (start !== false || end !== false) {
        if (start !== false) {
          criteria.push(DOC_STORE$1 + '.id ' + (descending ? '<=' : '>=') + ' ?');
          sqlArgs.push(start);
        }
        if (end !== false) {
          var comparator = descending ? '>' : '<';
          if (inclusiveEnd) {
            comparator += '=';
          }
          criteria.push(DOC_STORE$1 + '.id ' + comparator + ' ?');
          sqlArgs.push(end);
        }
        if (key !== false) {
          criteria.push(DOC_STORE$1 + '.id = ?');
          sqlArgs.push(key);
        }
      }
  
      if (opts.deleted !== 'ok') {
        // report deleted if keys are specified
        criteria.push(BY_SEQ_STORE$1 + '.deleted = 0');
      }
  
      db.readTransaction(function (tx) {
  
        // first count up the total rows
        countDocs(tx, function (count) {
          totalRows = count;
  
          if (limit === 0) {
            return;
          }
  
          // then actually fetch the documents
          var sql = select(
            SELECT_DOCS,
            [DOC_STORE$1, BY_SEQ_STORE$1],
            DOC_STORE_AND_BY_SEQ_JOINER,
            criteria,
            DOC_STORE$1 + '.id ' + (descending ? 'DESC' : 'ASC')
            );
          sql += ' LIMIT ' + limit + ' OFFSET ' + offset;
  
          tx.executeSql(sql, sqlArgs, function (tx, result) {
            for (var i = 0, l = result.rows.length; i < l; i++) {
              var item = result.rows.item(i);
              var metadata = safeJsonParse(item.metadata);
              var id = metadata.id;
              var data = unstringifyDoc(item.data, id, item.rev);
              var winningRev = data._rev;
              var doc = {
                id: id,
                key: id,
                value: {rev: winningRev}
              };
              if (opts.include_docs) {
                doc.doc = data;
                doc.doc._rev = winningRev;
                if (opts.conflicts) {
                  doc.doc._conflicts = collectConflicts(metadata);
                }
                fetchAttachmentsIfNecessary$1(doc.doc, opts, api, tx);
              }
              if (item.deleted) {
                if (opts.deleted === 'ok') {
                  doc.value.deleted = true;
                  doc.doc = null;
                } else {
                  continue;
                }
              }
              results.push(doc);
            }
          });
        });
      }, websqlError(callback), function () {
        callback(null, {
          total_rows: totalRows,
          offset: opts.skip,
          rows: results
        });
      });
    };
  
    api._changes = function (opts) {
      opts = clone(opts);
  
      if (opts.continuous) {
        var id = api._name + ':' + uuid();
        websqlChanges.addListener(api._name, id, api, opts);
        websqlChanges.notify(api._name);
        return {
          cancel: function () {
            websqlChanges.removeListener(api._name, id);
          }
        };
      }
  
      var descending = opts.descending;
  
      // Ignore the `since` parameter when `descending` is true
      opts.since = opts.since && !descending ? opts.since : 0;
  
      var limit = 'limit' in opts ? opts.limit : -1;
      if (limit === 0) {
        limit = 1; // per CouchDB _changes spec
      }
  
      var returnDocs;
      if ('return_docs' in opts) {
        returnDocs = opts.return_docs;
      } else if ('returnDocs' in opts) {
        // TODO: Remove 'returnDocs' in favor of 'return_docs' in a future release
        returnDocs = opts.returnDocs;
      } else {
        returnDocs = true;
      }
      var results = [];
      var numResults = 0;
  
      function fetchChanges() {
  
        var selectStmt =
          DOC_STORE$1 + '.json AS metadata, ' +
          DOC_STORE$1 + '.max_seq AS maxSeq, ' +
          BY_SEQ_STORE$1 + '.json AS winningDoc, ' +
          BY_SEQ_STORE$1 + '.rev AS winningRev ';
  
        var from = DOC_STORE$1 + ' JOIN ' + BY_SEQ_STORE$1;
  
        var joiner = DOC_STORE$1 + '.id=' + BY_SEQ_STORE$1 + '.doc_id' +
          ' AND ' + DOC_STORE$1 + '.winningseq=' + BY_SEQ_STORE$1 + '.seq';
  
        var criteria = ['maxSeq > ?'];
        var sqlArgs = [opts.since];
  
        if (opts.doc_ids) {
          criteria.push(DOC_STORE$1 + '.id IN ' + qMarks(opts.doc_ids.length));
          sqlArgs = sqlArgs.concat(opts.doc_ids);
        }
  
        var orderBy = 'maxSeq ' + (descending ? 'DESC' : 'ASC');
  
        var sql = select(selectStmt, from, joiner, criteria, orderBy);
  
        var filter = filterChange(opts);
        if (!opts.view && !opts.filter) {
          // we can just limit in the query
          sql += ' LIMIT ' + limit;
        }
  
        var lastSeq = opts.since || 0;
        db.readTransaction(function (tx) {
          tx.executeSql(sql, sqlArgs, function (tx, result) {
            function reportChange(change) {
              return function () {
                opts.onChange(change);
              };
            }
            for (var i = 0, l = result.rows.length; i < l; i++) {
              var item = result.rows.item(i);
              var metadata = safeJsonParse(item.metadata);
              lastSeq = item.maxSeq;
  
              var doc = unstringifyDoc(item.winningDoc, metadata.id,
                item.winningRev);
              var change = opts.processChange(doc, metadata, opts);
              change.seq = item.maxSeq;
  
              var filtered = filter(change);
              if (typeof filtered === 'object') {
                return opts.complete(filtered);
              }
  
              if (filtered) {
                numResults++;
                if (returnDocs) {
                  results.push(change);
                }
                // process the attachment immediately
                // for the benefit of live listeners
                if (opts.attachments && opts.include_docs) {
                  fetchAttachmentsIfNecessary$1(doc, opts, api, tx,
                    reportChange(change));
                } else {
                  reportChange(change)();
                }
              }
              if (numResults === limit) {
                break;
              }
            }
          });
        }, websqlError(opts.complete), function () {
          if (!opts.continuous) {
            opts.complete(null, {
              results: results,
              last_seq: lastSeq
            });
          }
        });
      }
  
      fetchChanges();
    };
  
    api._close = function (callback) {
      //WebSQL databases do not need to be closed
      callback();
    };
  
    api._getAttachment = function (docId, attachId, attachment, opts, callback) {
      var res;
      var tx = opts.ctx;
      var digest = attachment.digest;
      var type = attachment.content_type;
      var sql = 'SELECT escaped, ' +
        'CASE WHEN escaped = 1 THEN body ELSE HEX(body) END AS body FROM ' +
        ATTACH_STORE$1 + ' WHERE digest=?';
      tx.executeSql(sql, [digest], function (tx, result) {
        // websql has a bug where \u0000 causes early truncation in strings
        // and blobs. to work around this, we used to use the hex() function,
        // but that's not performant. after migration 6, we remove \u0000
        // and add it back in afterwards
        var item = result.rows.item(0);
        var data = item.escaped ? unescapeBlob(item.body) :
          parseHexString(item.body, encoding);
        if (opts.binary) {
          res = binStringToBluffer(data, type);
        } else {
          res = btoa$1(data);
        }
        callback(null, res);
      });
    };
  
    api._getRevisionTree = function (docId, callback) {
      db.readTransaction(function (tx) {
        var sql = 'SELECT json AS metadata FROM ' + DOC_STORE$1 + ' WHERE id = ?';
        tx.executeSql(sql, [docId], function (tx, result) {
          if (!result.rows.length) {
            callback(createError(MISSING_DOC));
          } else {
            var data = safeJsonParse(result.rows.item(0).metadata);
            callback(null, data.rev_tree);
          }
        });
      });
    };
  
    api._doCompaction = function (docId, revs, callback) {
      if (!revs.length) {
        return callback();
      }
      db.transaction(function (tx) {
  
        // update doc store
        var sql = 'SELECT json AS metadata FROM ' + DOC_STORE$1 + ' WHERE id = ?';
        tx.executeSql(sql, [docId], function (tx, result) {
          var metadata = safeJsonParse(result.rows.item(0).metadata);
          traverseRevTree(metadata.rev_tree, function (isLeaf, pos,
                                                             revHash, ctx, opts) {
            var rev = pos + '-' + revHash;
            if (revs.indexOf(rev) !== -1) {
              opts.status = 'missing';
            }
          });
  
          var sql = 'UPDATE ' + DOC_STORE$1 + ' SET json = ? WHERE id = ?';
          tx.executeSql(sql, [safeJsonStringify(metadata), docId]);
        });
  
        compactRevs$1(revs, docId, tx);
      }, websqlError(callback), function () {
        callback();
      });
    };
  
    api._getLocal = function (id, callback) {
      db.readTransaction(function (tx) {
        var sql = 'SELECT json, rev FROM ' + LOCAL_STORE$1 + ' WHERE id=?';
        tx.executeSql(sql, [id], function (tx, res) {
          if (res.rows.length) {
            var item = res.rows.item(0);
            var doc = unstringifyDoc(item.json, id, item.rev);
            callback(null, doc);
          } else {
            callback(createError(MISSING_DOC));
          }
        });
      });
    };
  
    api._putLocal = function (doc, opts, callback) {
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
      delete doc._revisions; // ignore this, trust the rev
      var oldRev = doc._rev;
      var id = doc._id;
      var newRev;
      if (!oldRev) {
        newRev = doc._rev = '0-1';
      } else {
        newRev = doc._rev = '0-' + (parseInt(oldRev.split('-')[1], 10) + 1);
      }
      var json = stringifyDoc(doc);
  
      var ret;
      function putLocal(tx) {
        var sql;
        var values;
        if (oldRev) {
          sql = 'UPDATE ' + LOCAL_STORE$1 + ' SET rev=?, json=? ' +
            'WHERE id=? AND rev=?';
          values = [newRev, json, id, oldRev];
        } else {
          sql = 'INSERT INTO ' + LOCAL_STORE$1 + ' (id, rev, json) VALUES (?,?,?)';
          values = [id, newRev, json];
        }
        tx.executeSql(sql, values, function (tx, res) {
          if (res.rowsAffected) {
            ret = {ok: true, id: id, rev: newRev};
            if (opts.ctx) { // return immediately
              callback(null, ret);
            }
          } else {
            callback(createError(REV_CONFLICT));
          }
        }, function () {
          callback(createError(REV_CONFLICT));
          return false; // ack that we handled the error
        });
      }
  
      if (opts.ctx) {
        putLocal(opts.ctx);
      } else {
        db.transaction(putLocal, websqlError(callback), function () {
          if (ret) {
            callback(null, ret);
          }
        });
      }
    };
  
    api._removeLocal = function (doc, opts, callback) {
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
      var ret;
  
      function removeLocal(tx) {
        var sql = 'DELETE FROM ' + LOCAL_STORE$1 + ' WHERE id=? AND rev=?';
        var params = [doc._id, doc._rev];
        tx.executeSql(sql, params, function (tx, res) {
          if (!res.rowsAffected) {
            return callback(createError(MISSING_DOC));
          }
          ret = {ok: true, id: doc._id, rev: '0-0'};
          if (opts.ctx) { // return immediately
            callback(null, ret);
          }
        });
      }
  
      if (opts.ctx) {
        removeLocal(opts.ctx);
      } else {
        db.transaction(removeLocal, websqlError(callback), function () {
          if (ret) {
            callback(null, ret);
          }
        });
      }
    };
  
    api._destroy = function (opts, callback) {
      websqlChanges.removeAllListeners(api._name);
      db.transaction(function (tx) {
        var stores = [DOC_STORE$1, BY_SEQ_STORE$1, ATTACH_STORE$1, META_STORE$1,
          LOCAL_STORE$1, ATTACH_AND_SEQ_STORE$1];
        stores.forEach(function (store) {
          tx.executeSql('DROP TABLE IF EXISTS ' + store, []);
        });
      }, websqlError(callback), function () {
        if (hasLocalStorage()) {
          delete window.localStorage['_pouch__websqldb_' + api._name];
          delete window.localStorage[api._name];
        }
        callback(null, {'ok': true});
      });
    };
  }
  
  function canOpenTestDB() {
    try {
      openDatabase('_pouch_validate_websql', 1, '', 1);
      return true;
    } catch (err) {
      return false;
    }
  }
  
  // WKWebView had a bug where WebSQL would throw a DOM Exception 18
  // (see https://bugs.webkit.org/show_bug.cgi?id=137760 and
  // https://github.com/pouchdb/pouchdb/issues/5079)
  // This has been fixed in latest WebKit, so we try to detect it here.
  function isValidWebSQL() {
    // WKWebView UA:
    //   Mozilla/5.0 (iPhone; CPU iPhone OS 9_2 like Mac OS X)
    //   AppleWebKit/601.1.46 (KHTML, like Gecko) Mobile/13C75
    // Chrome for iOS UA:
    //   Mozilla/5.0 (iPhone; U; CPU iPhone OS 5_1_1 like Mac OS X; en)
    //   AppleWebKit/534.46.0 (KHTML, like Gecko) CriOS/19.0.1084.60
    //   Mobile/9B206 Safari/7534.48.3
    // Firefox for iOS UA:
    //   Mozilla/5.0 (iPhone; CPU iPhone OS 8_3 like Mac OS X) AppleWebKit/600.1.4
    //   (KHTML, like Gecko) FxiOS/1.0 Mobile/12F69 Safari/600.1.4
  
    // indexedDB is null on some UIWebViews and undefined in others
    // see: https://bugs.webkit.org/show_bug.cgi?id=137034
    if (typeof indexedDB === 'undefined' || indexedDB === null ||
        !/iP(hone|od|ad)/.test(navigator.userAgent)) {
      // definitely not WKWebView, avoid creating an unnecessary database
      return true;
    }
    // Cache the result in LocalStorage. Reason we do this is because if we
    // call openDatabase() too many times, Safari craps out in SauceLabs and
    // starts throwing DOM Exception 14s.
    var hasLS = hasLocalStorage();
    // Include user agent in the hash, so that if Safari is upgraded, we don't
    // continually think it's broken.
    var localStorageKey = '_pouch__websqldb_valid_' + navigator.userAgent;
    if (hasLS && localStorage[localStorageKey]) {
      return localStorage[localStorageKey] === '1';
    }
    var openedTestDB = canOpenTestDB();
    if (hasLS) {
      localStorage[localStorageKey] = openedTestDB ? '1' : '0';
    }
    return openedTestDB;
  }
  
  function valid() {
    if (typeof openDatabase !== 'function') {
      return false;
    }
    return isValidWebSQL();
  }
  
  function openDB(name, version, description, size) {
    // Traditional WebSQL API
    return openDatabase(name, version, description, size);
  }
  
  function WebSQLPouch(opts, callback) {
    var _opts = jsExtend.extend({
      websql: openDB
    }, opts);
  
    WebSqlPouch$1.call(this, _opts, callback);
  }
  
  WebSQLPouch.valid = valid;
  
  WebSQLPouch.use_prefix = true;
  
  function WebSqlPouch (PouchDB) {
    PouchDB.adapter('websql', WebSQLPouch, true);
  }
  
  /* global fetch */
  /* global Headers */
  function wrappedFetch() {
    var wrappedPromise = {};
  
    var promise = new PouchPromise(function (resolve, reject) {
      wrappedPromise.resolve = resolve;
      wrappedPromise.reject = reject;
    });
  
    var args = new Array(arguments.length);
  
    for (var i = 0; i < args.length; i++) {
      args[i] = arguments[i];
    }
  
    wrappedPromise.promise = promise;
  
    PouchPromise.resolve().then(function () {
      return fetch.apply(null, args);
    }).then(function (response) {
      wrappedPromise.resolve(response);
    })["catch"](function (error) {
      wrappedPromise.reject(error);
    });
  
    return wrappedPromise;
  }
  
  function fetchRequest(options, callback) {
    var wrappedPromise, timer, response;
  
    var headers = new Headers();
  
    var fetchOptions = {
      method: options.method,
      credentials: 'include',
      headers: headers
    };
  
    if (options.json) {
      headers.set('Accept', 'application/json');
      headers.set('Content-Type', options.headers['Content-Type'] ||
        'application/json');
    }
  
    if (options.body && (options.body instanceof Blob)) {
      readAsArrayBuffer(options.body, function (arrayBuffer) {
        fetchOptions.body = arrayBuffer;
      });
    } else if (options.body &&
               options.processData &&
               typeof options.body !== 'string') {
      fetchOptions.body = JSON.stringify(options.body);
    } else if ('body' in options) {
      fetchOptions.body = options.body;
    } else {
      fetchOptions.body = null;
    }
  
    Object.keys(options.headers).forEach(function (key) {
      if (options.headers.hasOwnProperty(key)) {
        headers.set(key, options.headers[key]);
      }
    });
  
    wrappedPromise = wrappedFetch(options.url, fetchOptions);
  
    if (options.timeout > 0) {
      timer = setTimeout(function () {
        wrappedPromise.reject(new Error('Load timeout for resource: ' +
          options.url));
      }, options.timeout);
    }
  
    wrappedPromise.promise.then(function (fetchResponse) {
      response = {
        statusCode: fetchResponse.status
      };
  
      if (options.timeout > 0) {
        clearTimeout(timer);
      }
  
      if (response.statusCode >= 200 && response.statusCode < 300) {
        return options.binary ? fetchResponse.blob() : fetchResponse.text();
      }
  
      return fetchResponse.json();
    }).then(function (result) {
      if (response.statusCode >= 200 && response.statusCode < 300) {
        callback(null, response, result);
      } else {
        callback(result, response);
      }
    })["catch"](function (error) {
      callback(error, response);
    });
  
    return {abort: wrappedPromise.reject};
  }
  
  function xhRequest(options, callback) {
  
    var xhr, timer;
    var timedout = false;
  
    var abortReq = function () {
      xhr.abort();
      cleanUp();
    };
  
    var timeoutReq = function () {
      timedout = true;
      xhr.abort();
      cleanUp();
    };
  
    var ret = {abort: abortReq};
  
    var cleanUp = function () {
      clearTimeout(timer);
      ret.abort = function () {};
      if (xhr) {
        xhr.onprogress = undefined;
        if (xhr.upload) {
          xhr.upload.onprogress = undefined;
        }
        xhr.onreadystatechange = undefined;
        xhr = undefined;
      }
    };
  
    if (options.xhr) {
      xhr = new options.xhr();
    } else {
      xhr = new XMLHttpRequest();
    }
  
    try {
      xhr.open(options.method, options.url);
    } catch (exception) {
      return callback(new Error(exception.name || 'Url is invalid'));
    }
  
    xhr.withCredentials = ('withCredentials' in options) ?
      options.withCredentials : true;
  
    if (options.method === 'GET') {
      delete options.headers['Content-Type'];
    } else if (options.json) {
      options.headers.Accept = 'application/json';
      options.headers['Content-Type'] = options.headers['Content-Type'] ||
        'application/json';
      if (options.body &&
          options.processData &&
          typeof options.body !== "string") {
        options.body = JSON.stringify(options.body);
      }
    }
  
    if (options.binary) {
      xhr.responseType = 'arraybuffer';
    }
  
    if (!('body' in options)) {
      options.body = null;
    }
  
    for (var key in options.headers) {
      if (options.headers.hasOwnProperty(key)) {
        xhr.setRequestHeader(key, options.headers[key]);
      }
    }
  
    if (options.timeout > 0) {
      timer = setTimeout(timeoutReq, options.timeout);
      xhr.onprogress = function () {
        clearTimeout(timer);
        if(xhr.readyState !== 4) {
          timer = setTimeout(timeoutReq, options.timeout);
        }
      };
      if (typeof xhr.upload !== 'undefined') { // does not exist in ie9
        xhr.upload.onprogress = xhr.onprogress;
      }
    }
  
    xhr.onreadystatechange = function () {
      if (xhr.readyState !== 4) {
        return;
      }
  
      var response = {
        statusCode: xhr.status
      };
  
      if (xhr.status >= 200 && xhr.status < 300) {
        var data;
        if (options.binary) {
          data = createBlob([xhr.response || ''], {
            type: xhr.getResponseHeader('Content-Type')
          });
        } else {
          data = xhr.responseText;
        }
        callback(null, response, data);
      } else {
        var err = {};
        if (timedout) {
          err = new Error('ETIMEDOUT');
          err.code = 'ETIMEDOUT';
        } else if (typeof xhr.response === 'string') {
          try {
            err = JSON.parse(xhr.response);
          } catch(e) {}
        }
        err.status = xhr.status;
        callback(err);
      }
      cleanUp();
    };
  
    if (options.body && (options.body instanceof Blob)) {
      readAsArrayBuffer(options.body, function (arrayBuffer) {
        xhr.send(arrayBuffer);
      });
    } else {
      xhr.send(options.body);
    }
  
    return ret;
  }
  
  function testXhr() {
    try {
      new XMLHttpRequest();
      return true;
    } catch (err) {
      return false;
    }
  }
  
  var hasXhr = testXhr();
  
  function ajax$1(options, callback) {
    if (hasXhr || options.xhr) {
      return xhRequest(options, callback);
    } else {
      return fetchRequest(options, callback);
    }
  }
  
  // the blob already has a type; do nothing
  var res$2 = function () {};
  
  function defaultBody() {
    return '';
  }
  
  function ajaxCore(options, callback) {
  
    options = clone(options);
  
    var defaultOptions = {
      method : "GET",
      headers: {},
      json: true,
      processData: true,
      timeout: 10000,
      cache: false
    };
  
    options = jsExtend.extend(defaultOptions, options);
  
    function onSuccess(obj, resp, cb) {
      if (!options.binary && options.json && typeof obj === 'string') {
        /* istanbul ignore next */
        try {
          obj = JSON.parse(obj);
        } catch (e) {
          // Probably a malformed JSON from server
          return cb(e);
        }
      }
      if (Array.isArray(obj)) {
        obj = obj.map(function (v) {
          if (v.error || v.missing) {
            return generateErrorFromResponse(v);
          } else {
            return v;
          }
        });
      }
      if (options.binary) {
        res$2(obj, resp);
      }
      cb(null, obj, resp);
    }
  
    if (options.json) {
      if (!options.binary) {
        options.headers.Accept = 'application/json';
      }
      options.headers['Content-Type'] = options.headers['Content-Type'] ||
        'application/json';
    }
  
    if (options.binary) {
      options.encoding = null;
      options.json = false;
    }
  
    if (!options.processData) {
      options.json = false;
    }
  
    return ajax$1(options, function (err, response, body) {
  
      if (err) {
        return callback(generateErrorFromResponse(err));
      }
  
      var error;
      var content_type = response.headers && response.headers['content-type'];
      var data = body || defaultBody();
  
      // CouchDB doesn't always return the right content-type for JSON data, so
      // we check for ^{ and }$ (ignoring leading/trailing whitespace)
      if (!options.binary && (options.json || !options.processData) &&
          typeof data !== 'object' &&
          (/json/.test(content_type) ||
           (/^[\s]*\{/.test(data) && /\}[\s]*$/.test(data)))) {
        try {
          data = JSON.parse(data.toString());
        } catch (e) {}
      }
  
      if (response.statusCode >= 200 && response.statusCode < 300) {
        onSuccess(data, response, callback);
      } else {
        error = generateErrorFromResponse(data);
        error.status = response.statusCode;
        callback(error);
      }
    });
  }
  
  function ajax(opts, callback) {
  
    // cache-buster, specifically designed to work around IE's aggressive caching
    // see http://www.dashbay.com/2011/05/internet-explorer-caches-ajax/
    // Also Safari caches POSTs, so we need to cache-bust those too.
    var ua = (navigator && navigator.userAgent) ?
      navigator.userAgent.toLowerCase() : '';
  
    var isSafari = ua.indexOf('safari') !== -1 && ua.indexOf('chrome') === -1;
    var isIE = ua.indexOf('msie') !== -1;
    var isEdge = ua.indexOf('edge') !== -1;
  
    // it appears the new version of safari also caches GETs,
    // see https://github.com/pouchdb/pouchdb/issues/5010
    var shouldCacheBust = (isSafari ||
      ((isIE || isEdge) && opts.method === 'GET'));
  
    var cache = 'cache' in opts ? opts.cache : true;
  
    var isBlobUrl = /^blob:/.test(opts.url); // don't append nonces for blob URLs
  
    if (!isBlobUrl && (shouldCacheBust || !cache)) {
      var hasArgs = opts.url.indexOf('?') !== -1;
      opts.url += (hasArgs ? '&' : '?') + '_nonce=' + Date.now();
    }
  
    return ajaxCore(opts, callback);
  }
  
  var CHANGES_BATCH_SIZE = 25;
  var MAX_SIMULTANEOUS_REVS = 50;
  
  var supportsBulkGetMap = {};
  
  var log$1 = debug('pouchdb:http');
  
  function readAttachmentsAsBlobOrBuffer(row) {
    var atts = row.doc && row.doc._attachments;
    if (!atts) {
      return;
    }
    Object.keys(atts).forEach(function (filename) {
      var att = atts[filename];
      att.data = b64ToBluffer(att.data, att.content_type);
    });
  }
  
  function encodeDocId(id) {
    if (/^_design/.test(id)) {
      return '_design/' + encodeURIComponent(id.slice(8));
    }
    if (/^_local/.test(id)) {
      return '_local/' + encodeURIComponent(id.slice(7));
    }
    return encodeURIComponent(id);
  }
  
  function preprocessAttachments$1(doc) {
    if (!doc._attachments || !Object.keys(doc._attachments)) {
      return PouchPromise.resolve();
    }
  
    return PouchPromise.all(Object.keys(doc._attachments).map(function (key) {
      var attachment = doc._attachments[key];
      if (attachment.data && typeof attachment.data !== 'string') {
        return new PouchPromise(function (resolve) {
          blobToBase64(attachment.data, resolve);
        }).then(function (b64) {
          attachment.data = b64;
        });
      }
    }));
  }
  
  function hasUrlPrefix(opts) {
    if (!opts.prefix) {
      return false;
    }
  
    var protocol = parseUri(opts.prefix).protocol;
  
    return protocol === 'http' || protocol === 'https';
  }
  
  // Get all the information you possibly can about the URI given by name and
  // return it as a suitable object.
  function getHost(name, opts) {
  
    // encode db name if opts.prefix is a url (#5574)
    if (hasUrlPrefix(opts)) {
      var dbName = opts.name.substr(opts.prefix.length);
      name = opts.prefix + encodeURIComponent(dbName);
    }
  
    // Prase the URI into all its little bits
    var uri = parseUri(name);
  
    // Store the user and password as a separate auth object
    if (uri.user || uri.password) {
      uri.auth = {username: uri.user, password: uri.password};
    }
  
    // Split the path part of the URI into parts using '/' as the delimiter
    // after removing any leading '/' and any trailing '/'
    var parts = uri.path.replace(/(^\/|\/$)/g, '').split('/');
  
    // Store the first part as the database name and remove it from the parts
    // array
    uri.db = parts.pop();
    // Prevent double encoding of URI component
    if (uri.db.indexOf('%') === -1) {
      uri.db = encodeURIComponent(uri.db);
    }
  
    // Restore the path by joining all the remaining parts (all the parts
    // except for the database name) with '/'s
    uri.path = parts.join('/');
  
    return uri;
  }
  
  // Generate a URL with the host data given by opts and the given path
  function genDBUrl(opts, path) {
    return genUrl(opts, opts.db + '/' + path);
  }
  
  // Generate a URL with the host data given by opts and the given path
  function genUrl(opts, path) {
    // If the host already has a path, then we need to have a path delimiter
    // Otherwise, the path delimiter is the empty string
    var pathDel = !opts.path ? '' : '/';
  
    // If the host already has a path, then we need to have a path delimiter
    // Otherwise, the path delimiter is the empty string
    return opts.protocol + '://' + opts.host +
           (opts.port ? (':' + opts.port) : '') +
           '/' + opts.path + pathDel + path;
  }
  
  function paramsToStr(params) {
    return '?' + Object.keys(params).map(function (k) {
      return k + '=' + encodeURIComponent(params[k]);
    }).join('&');
  }
  
  // Implements the PouchDB API for dealing with CouchDB instances over HTTP
  function HttpPouch(opts, callback) {
  
    // The functions that will be publicly available for HttpPouch
    var api = this;
  
    var host = getHost(opts.name, opts);
    var dbUrl = genDBUrl(host, '');
  
    opts = clone(opts);
    var ajaxOpts = opts.ajax || {};
  
    if (opts.auth || host.auth) {
      var nAuth = opts.auth || host.auth;
      var str = nAuth.username + ':' + nAuth.password;
      var token = btoa$1(unescape(encodeURIComponent(str)));
      ajaxOpts.headers = ajaxOpts.headers || {};
      ajaxOpts.headers.Authorization = 'Basic ' + token;
    }
  
    // Not strictly necessary, but we do this because numerous tests
    // rely on swapping ajax in and out.
    api._ajax = ajax;
  
    function ajax$$(userOpts, options, callback) {
      var reqAjax = userOpts.ajax || {};
      var reqOpts = jsExtend.extend(clone(ajaxOpts), reqAjax, options);
      log$1(reqOpts.method + ' ' + reqOpts.url);
      return api._ajax(reqOpts, callback);
    }
  
    function ajaxPromise(userOpts, opts) {
      return new PouchPromise(function (resolve, reject) {
        ajax$$(userOpts, opts, function (err, res) {
          /* istanbul ignore if */
          if (err) {
            return reject(err);
          }
          resolve(res);
        });
      });
    }
  
    function adapterFun$$(name, fun) {
      return adapterFun(name, getArguments(function (args) {
        setup().then(function () {
          return fun.apply(this, args);
        })["catch"](function (e) {
          var callback = args.pop();
          callback(e);
        });
      }));
    }
  
    var setupPromise;
  
    function setup() {
      // TODO: Remove `skipSetup` in favor of `skip_setup` in a future release
      if (opts.skipSetup || opts.skip_setup) {
        return PouchPromise.resolve();
      }
  
      // If there is a setup in process or previous successful setup
      // done then we will use that
      // If previous setups have been rejected we will try again
      if (setupPromise) {
        return setupPromise;
      }
  
      var checkExists = {method: 'GET', url: dbUrl};
      setupPromise = ajaxPromise({}, checkExists)["catch"](function (err) {
        if (err && err.status && err.status === 404) {
          // Doesnt exist, create it
          explainError(404, 'PouchDB is just detecting if the remote exists.');
          return ajaxPromise({}, {method: 'PUT', url: dbUrl});
        } else {
          return PouchPromise.reject(err);
        }
      })["catch"](function (err) {
        // If we try to create a database that already exists, skipped in
        // istanbul since its catching a race condition.
        /* istanbul ignore if */
        if (err && err.status && err.status === 412) {
          return true;
        }
        return PouchPromise.reject(err);
      });
  
      setupPromise["catch"](function () {
        setupPromise = null;
      });
  
      return setupPromise;
    }
  
    setTimeout(function () {
      callback(null, api);
    });
  
    api.type = function () {
      return 'http';
    };
  
    api.id = adapterFun$$('id', function (callback) {
      ajax$$({}, {method: 'GET', url: genUrl(host, '')}, function (err, result) {
        var uuid = (result && result.uuid) ?
          (result.uuid + host.db) : genDBUrl(host, '');
        callback(null, uuid);
      });
    });
  
    api.request = adapterFun$$('request', function (options, callback) {
      options.url = genDBUrl(host, options.url);
      ajax$$({}, options, callback);
    });
  
    // Sends a POST request to the host calling the couchdb _compact function
    //    version: The version of CouchDB it is running
    api.compact = adapterFun$$('compact', function (opts, callback) {
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
      opts = clone(opts);
      ajax$$(opts, {
        url: genDBUrl(host, '_compact'),
        method: 'POST'
      }, function () {
        function ping() {
          api.info(function (err, res) {
            if (res && !res.compact_running) {
              callback(null, {ok: true});
            } else {
              setTimeout(ping, opts.interval || 200);
            }
          });
        }
        // Ping the http if it's finished compaction
        ping();
      });
    });
  
    api.bulkGet = adapterFun('bulkGet', function (opts, callback) {
      var self = this;
  
      function doBulkGet(cb) {
        var params = {};
        if (opts.revs) {
          params.revs = true;
        }
        if (opts.attachments) {
          /* istanbul ignore next */
          params.attachments = true;
        }
        ajax$$({}, {
          url: genDBUrl(host, '_bulk_get' + paramsToStr(params)),
          method: 'POST',
          body: { docs: opts.docs}
        }, cb);
      }
  
      function doBulkGetShim() {
        // avoid "url too long error" by splitting up into multiple requests
        var batchSize = MAX_SIMULTANEOUS_REVS;
        var numBatches = Math.ceil(opts.docs.length / batchSize);
        var numDone = 0;
        var results = new Array(numBatches);
  
        function onResult(batchNum) {
          return function (err, res) {
            // err is impossible because shim returns a list of errs in that case
            results[batchNum] = res.results;
            if (++numDone === numBatches) {
              callback(null, {results: flatten(results)});
            }
          };
        }
  
        for (var i = 0; i < numBatches; i++) {
          var subOpts = pick(opts, ['revs', 'attachments']);
          subOpts.ajax = ajaxOpts;
          subOpts.docs = opts.docs.slice(i * batchSize,
            Math.min(opts.docs.length, (i + 1) * batchSize));
          bulkGet(self, subOpts, onResult(i));
        }
      }
  
      // mark the whole database as either supporting or not supporting _bulk_get
      var dbUrl = genUrl(host, '');
      var supportsBulkGet = supportsBulkGetMap[dbUrl];
  
      if (typeof supportsBulkGet !== 'boolean') {
        // check if this database supports _bulk_get
        doBulkGet(function (err, res) {
          /* istanbul ignore else */
          if (err) {
            var status = Math.floor(err.status / 100);
            /* istanbul ignore else */
            if (status === 4 || status === 5) { // 40x or 50x
              supportsBulkGetMap[dbUrl] = false;
              explainError(
                err.status,
                'PouchDB is just detecting if the remote ' +
                'supports the _bulk_get API.'
              );
              doBulkGetShim();
            } else {
              callback(err);
            }
          } else {
            supportsBulkGetMap[dbUrl] = true;
            callback(null, res);
          }
        });
      } else if (supportsBulkGet) {
        /* istanbul ignore next */
        doBulkGet(callback);
      } else {
        doBulkGetShim();
      }
    });
  
    // Calls GET on the host, which gets back a JSON string containing
    //    couchdb: A welcome string
    //    version: The version of CouchDB it is running
    api._info = function (callback) {
      setup().then(function () {
        ajax$$({}, {
          method: 'GET',
          url: genDBUrl(host, '')
        }, function (err, res) {
          /* istanbul ignore next */
          if (err) {
          return callback(err);
          }
          res.host = genDBUrl(host, '');
          callback(null, res);
        });
      })["catch"](callback);
    };
  
    // Get the document with the given id from the database given by host.
    // The id could be solely the _id in the database, or it may be a
    // _design/ID or _local/ID path
    api.get = adapterFun$$('get', function (id, opts, callback) {
      // If no options were given, set the callback to the second parameter
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
      opts = clone(opts);
  
      // List of parameters to add to the GET request
      var params = {};
  
      if (opts.revs) {
        params.revs = true;
      }
  
      if (opts.revs_info) {
        params.revs_info = true;
      }
  
      if (opts.open_revs) {
        if (opts.open_revs !== "all") {
          opts.open_revs = JSON.stringify(opts.open_revs);
        }
        params.open_revs = opts.open_revs;
      }
  
      if (opts.rev) {
        params.rev = opts.rev;
      }
  
      if (opts.conflicts) {
        params.conflicts = opts.conflicts;
      }
  
      id = encodeDocId(id);
  
      // Set the options for the ajax call
      var options = {
        method: 'GET',
        url: genDBUrl(host, id + paramsToStr(params))
      };
  
      function fetchAttachments(doc) {
        var atts = doc._attachments;
        var filenames = atts && Object.keys(atts);
        if (!atts || !filenames.length) {
          return;
        }
        // we fetch these manually in separate XHRs, because
        // Sync Gateway would normally send it back as multipart/mixed,
        // which we cannot parse. Also, this is more efficient than
        // receiving attachments as base64-encoded strings.
        function fetch() {
  
          if (!filenames.length) {
            return null;
          }
  
          var filename = filenames.pop();
          var att = atts[filename];
          var path = encodeDocId(doc._id) + '/' + encodeAttachmentId(filename) +
            '?rev=' + doc._rev;
          return ajaxPromise(opts, {
            method: 'GET',
            url: genDBUrl(host, path),
            binary: true
          }).then(function (blob) {
            if (opts.binary) {
              return blob;
            }
            return new PouchPromise(function (resolve) {
              blobToBase64(blob, resolve);
            });
          }).then(function (data) {
            delete att.stub;
            delete att.length;
            att.data = data;
          });
        }
  
        // This limits the number of parallel xhr requests to 5 any time
        // to avoid issues with maximum browser request limits
        return new PromisePool(fetch, 5, {promise: PouchPromise}).start();
      }
  
      function fetchAllAttachments(docOrDocs) {
        if (Array.isArray(docOrDocs)) {
          return PouchPromise.all(docOrDocs.map(function (doc) {
            if (doc.ok) {
              return fetchAttachments(doc.ok);
            }
          }));
        }
        return fetchAttachments(docOrDocs);
      }
  
      ajaxPromise(opts, options).then(function (res) {
        return PouchPromise.resolve().then(function () {
          if (opts.attachments) {
            return fetchAllAttachments(res);
          }
        }).then(function () {
          callback(null, res);
        });
      })["catch"](callback);
    });
  
    // Delete the document given by doc from the database given by host.
    api.remove = adapterFun$$('remove',
        function (docOrId, optsOrRev, opts, callback) {
      var doc;
      if (typeof optsOrRev === 'string') {
        // id, rev, opts, callback style
        doc = {
          _id: docOrId,
          _rev: optsOrRev
        };
        if (typeof opts === 'function') {
          callback = opts;
          opts = {};
        }
      } else {
        // doc, opts, callback style
        doc = docOrId;
        if (typeof optsOrRev === 'function') {
          callback = optsOrRev;
          opts = {};
        } else {
          callback = opts;
          opts = optsOrRev;
        }
      }
  
      var rev = (doc._rev || opts.rev);
  
      // Delete the document
      ajax$$(opts, {
        method: 'DELETE',
        url: genDBUrl(host, encodeDocId(doc._id)) + '?rev=' + rev
      }, callback);
    });
  
    function encodeAttachmentId(attachmentId) {
      return attachmentId.split("/").map(encodeURIComponent).join("/");
    }
  
    // Get the attachment
    api.getAttachment =
      adapterFun$$('getAttachment', function (docId, attachmentId, opts,
                                                  callback) {
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
      var params = opts.rev ? ('?rev=' + opts.rev) : '';
      var url = genDBUrl(host, encodeDocId(docId)) + '/' +
        encodeAttachmentId(attachmentId) + params;
      ajax$$(opts, {
        method: 'GET',
        url: url,
        binary: true
      }, callback);
    });
  
    // Remove the attachment given by the id and rev
    api.removeAttachment =
      adapterFun$$('removeAttachment', function (docId, attachmentId, rev,
                                                     callback) {
  
      var url = genDBUrl(host, encodeDocId(docId) + '/' +
        encodeAttachmentId(attachmentId)) + '?rev=' + rev;
  
      ajax$$({}, {
        method: 'DELETE',
        url: url
      }, callback);
    });
  
    // Add the attachment given by blob and its contentType property
    // to the document with the given id, the revision given by rev, and
    // add it to the database given by host.
    api.putAttachment =
      adapterFun$$('putAttachment', function (docId, attachmentId, rev, blob,
                                                  type, callback) {
      if (typeof type === 'function') {
        callback = type;
        type = blob;
        blob = rev;
        rev = null;
      }
      var id = encodeDocId(docId) + '/' + encodeAttachmentId(attachmentId);
      var url = genDBUrl(host, id);
      if (rev) {
        url += '?rev=' + rev;
      }
  
      if (typeof blob === 'string') {
        // input is assumed to be a base64 string
        var binary;
        try {
          binary = atob$1(blob);
        } catch (err) {
          return callback(createError(BAD_ARG,
                          'Attachment is not a valid base64 string'));
        }
        blob = binary ? binStringToBluffer(binary, type) : '';
      }
  
      var opts = {
        headers: {'Content-Type': type},
        method: 'PUT',
        url: url,
        processData: false,
        body: blob,
        timeout: ajaxOpts.timeout || 60000
      };
      // Add the attachment
      ajax$$({}, opts, callback);
    });
  
    // Update/create multiple documents given by req in the database
    // given by host.
    api._bulkDocs = function (req, opts, callback) {
      // If new_edits=false then it prevents the database from creating
      // new revision numbers for the documents. Instead it just uses
      // the old ones. This is used in database replication.
      req.new_edits = opts.new_edits;
  
      setup().then(function () {
        return PouchPromise.all(req.docs.map(preprocessAttachments$1));
      }).then(function () {
        // Update/create the documents
        ajax$$(opts, {
          method: 'POST',
          url: genDBUrl(host, '_bulk_docs'),
          timeout: opts.timeout,
          body: req
        }, function (err, results) {
          if (err) {
            return callback(err);
          }
          results.forEach(function (result) {
            result.ok = true; // smooths out cloudant not adding this
          });
          callback(null, results);
        });
      })["catch"](callback);
    };
  
  
    // Update/create document
    api._put = function (doc, opts, callback) {
      setup().then(function () {
        return preprocessAttachments$1(doc);
      }).then(function () {
        // Update/create the document
        ajax$$(opts, {
          method: 'PUT',
          url: genDBUrl(host, encodeDocId(doc._id)),
          body: doc
        }, function (err, result) {
          if (err) {
            return callback(err);
          }
          callback(null, result);
        });
      })["catch"](callback);
    };
  
  
    // Get a listing of the documents in the database given
    // by host and ordered by increasing id.
    api.allDocs = adapterFun$$('allDocs', function (opts, callback) {
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
      opts = clone(opts);
  
      // List of parameters to add to the GET request
      var params = {};
      var body;
      var method = 'GET';
  
      if (opts.conflicts) {
        params.conflicts = true;
      }
  
      if (opts.descending) {
        params.descending = true;
      }
  
      if (opts.include_docs) {
        params.include_docs = true;
      }
  
      // added in CouchDB 1.6.0
      if (opts.attachments) {
        params.attachments = true;
      }
  
      if (opts.key) {
        params.key = JSON.stringify(opts.key);
      }
  
      if (opts.start_key) {
        opts.startkey = opts.start_key;
      }
  
      if (opts.startkey) {
        params.startkey = JSON.stringify(opts.startkey);
      }
  
      if (opts.end_key) {
        opts.endkey = opts.end_key;
      }
  
      if (opts.endkey) {
        params.endkey = JSON.stringify(opts.endkey);
      }
  
      if (typeof opts.inclusive_end !== 'undefined') {
        params.inclusive_end = !!opts.inclusive_end;
      }
  
      if (typeof opts.limit !== 'undefined') {
        params.limit = opts.limit;
      }
  
      if (typeof opts.skip !== 'undefined') {
        params.skip = opts.skip;
      }
  
      var paramStr = paramsToStr(params);
  
      if (typeof opts.keys !== 'undefined') {
        method = 'POST';
        body = {keys: opts.keys};
      }
  
      // Get the document listing
      ajaxPromise(opts, {
        method: method,
        url: genDBUrl(host, '_all_docs' + paramStr),
        body: body
      }).then(function (res) {
        if (opts.include_docs && opts.attachments && opts.binary) {
          res.rows.forEach(readAttachmentsAsBlobOrBuffer);
        }
        callback(null, res);
      })["catch"](callback);
    });
  
    // Get a list of changes made to documents in the database given by host.
    // TODO According to the README, there should be two other methods here,
    // api.changes.addListener and api.changes.removeListener.
    api._changes = function (opts) {
  
      // We internally page the results of a changes request, this means
      // if there is a large set of changes to be returned we can start
      // processing them quicker instead of waiting on the entire
      // set of changes to return and attempting to process them at once
      var batchSize = 'batch_size' in opts ? opts.batch_size : CHANGES_BATCH_SIZE;
  
      opts = clone(opts);
      opts.timeout = ('timeout' in opts) ? opts.timeout :
        ('timeout' in ajaxOpts) ? ajaxOpts.timeout :
        30 * 1000;
  
      // We give a 5 second buffer for CouchDB changes to respond with
      // an ok timeout (if a timeout it set)
      var params = opts.timeout ? {timeout: opts.timeout - (5 * 1000)} : {};
      var limit = (typeof opts.limit !== 'undefined') ? opts.limit : false;
      var returnDocs;
      if ('return_docs' in opts) {
        returnDocs = opts.return_docs;
      } else if ('returnDocs' in opts) {
        // TODO: Remove 'returnDocs' in favor of 'return_docs' in a future release
        returnDocs = opts.returnDocs;
      } else {
        returnDocs = true;
      }
      //
      var leftToFetch = limit;
  
      if (opts.style) {
        params.style = opts.style;
      }
  
      if (opts.include_docs || opts.filter && typeof opts.filter === 'function') {
        params.include_docs = true;
      }
  
      if (opts.attachments) {
        params.attachments = true;
      }
  
      if (opts.continuous) {
        params.feed = 'longpoll';
      }
  
      if (opts.conflicts) {
        params.conflicts = true;
      }
  
      if (opts.descending) {
        params.descending = true;
      }
  
      if ('heartbeat' in opts) {
        // If the heartbeat value is false, it disables the default heartbeat
        if (opts.heartbeat) {
          params.heartbeat = opts.heartbeat;
        }
      } else {
        // Default heartbeat to 10 seconds
        params.heartbeat = 10000;
      }
  
      if (opts.filter && typeof opts.filter === 'string') {
        params.filter = opts.filter;
      }
  
      if (opts.view && typeof opts.view === 'string') {
        params.filter = '_view';
        params.view = opts.view;
      }
  
      // If opts.query_params exists, pass it through to the changes request.
      // These parameters may be used by the filter on the source database.
      if (opts.query_params && typeof opts.query_params === 'object') {
        for (var param_name in opts.query_params) {
          /* istanbul ignore else */
          if (opts.query_params.hasOwnProperty(param_name)) {
            params[param_name] = opts.query_params[param_name];
          }
        }
      }
  
      var method = 'GET';
      var body;
  
      if (opts.doc_ids) {
        // set this automagically for the user; it's annoying that couchdb
        // requires both a "filter" and a "doc_ids" param.
        params.filter = '_doc_ids';
        method = 'POST';
        body = {doc_ids: opts.doc_ids };
      }
  
      var xhr;
      var lastFetchedSeq;
  
      // Get all the changes starting wtih the one immediately after the
      // sequence number given by since.
      var fetch = function (since, callback) {
        if (opts.aborted) {
          return;
        }
        params.since = since;
        // "since" can be any kind of json object in Coudant/CouchDB 2.x
        /* istanbul ignore next */
        if (typeof params.since === "object") {
          params.since = JSON.stringify(params.since);
        }
  
        if (opts.descending) {
          if (limit) {
            params.limit = leftToFetch;
          }
        } else {
          params.limit = (!limit || leftToFetch > batchSize) ?
            batchSize : leftToFetch;
        }
  
        // Set the options for the ajax call
        var xhrOpts = {
          method: method,
          url: genDBUrl(host, '_changes' + paramsToStr(params)),
          timeout: opts.timeout,
          body: body
        };
        lastFetchedSeq = since;
  
        /* istanbul ignore if */
        if (opts.aborted) {
          return;
        }
  
        // Get the changes
        setup().then(function () {
          xhr = ajax$$(opts, xhrOpts, callback);
        })["catch"](callback);
      };
  
      // If opts.since exists, get all the changes from the sequence
      // number given by opts.since. Otherwise, get all the changes
      // from the sequence number 0.
      var results = {results: []};
  
      var fetched = function (err, res) {
        if (opts.aborted) {
          return;
        }
        var raw_results_length = 0;
        // If the result of the ajax call (res) contains changes (res.results)
        if (res && res.results) {
          raw_results_length = res.results.length;
          results.last_seq = res.last_seq;
          // For each change
          var req = {};
          req.query = opts.query_params;
          res.results = res.results.filter(function (c) {
            leftToFetch--;
            var ret = filterChange(opts)(c);
            if (ret) {
              if (opts.include_docs && opts.attachments && opts.binary) {
                readAttachmentsAsBlobOrBuffer(c);
              }
              if (returnDocs) {
                results.results.push(c);
              }
              opts.onChange(c);
            }
            return ret;
          });
        } else if (err) {
          // In case of an error, stop listening for changes and call
          // opts.complete
          opts.aborted = true;
          opts.complete(err);
          return;
        }
  
        // The changes feed may have timed out with no results
        // if so reuse last update sequence
        if (res && res.last_seq) {
          lastFetchedSeq = res.last_seq;
        }
  
        var finished = (limit && leftToFetch <= 0) ||
          (res && raw_results_length < batchSize) ||
          (opts.descending);
  
        if ((opts.continuous && !(limit && leftToFetch <= 0)) || !finished) {
          // Queue a call to fetch again with the newest sequence number
          setTimeout(function () { fetch(lastFetchedSeq, fetched); }, 0);
        } else {
          // We're done, call the callback
          opts.complete(null, results);
        }
      };
  
      fetch(opts.since || 0, fetched);
  
      // Return a method to cancel this method from processing any more
      return {
        cancel: function () {
          opts.aborted = true;
          if (xhr) {
            xhr.abort();
          }
        }
      };
    };
  
    // Given a set of document/revision IDs (given by req), tets the subset of
    // those that do NOT correspond to revisions stored in the database.
    // See http://wiki.apache.org/couchdb/HttpPostRevsDiff
    api.revsDiff = adapterFun$$('revsDiff', function (req, opts, callback) {
      // If no options were given, set the callback to be the second parameter
      if (typeof opts === 'function') {
        callback = opts;
        opts = {};
      }
  
      // Get the missing document/revision IDs
      ajax$$(opts, {
        method: 'POST',
        url: genDBUrl(host, '_revs_diff'),
        body: req
      }, callback);
    });
  
    api._close = function (callback) {
      callback();
    };
  
    api._destroy = function (options, callback) {
      ajax$$(options, {
        url: genDBUrl(host, ''),
        method: 'DELETE'
      }, function (err, resp) {
        if (err && err.status && err.status !== 404) {
          return callback(err);
        }
        callback(null, resp);
      });
    };
  }
  
  // HttpPouch is a valid adapter.
  HttpPouch.valid = function () {
    return true;
  };
  
  function HttpPouch$1 (PouchDB) {
    PouchDB.adapter('http', HttpPouch, false);
    PouchDB.adapter('https', HttpPouch, false);
  }
  
  function pad(str, padWith, upToLength) {
    var padding = '';
    var targetLength = upToLength - str.length;
    /* istanbul ignore next */
    while (padding.length < targetLength) {
      padding += padWith;
    }
    return padding;
  }
  
  function padLeft(str, padWith, upToLength) {
    var padding = pad(str, padWith, upToLength);
    return padding + str;
  }
  
  var MIN_MAGNITUDE = -324; // verified by -Number.MIN_VALUE
  var MAGNITUDE_DIGITS = 3; // ditto
  var SEP = ''; // set to '_' for easier debugging 
  
  function collate(a, b) {
  
    if (a === b) {
      return 0;
    }
  
    a = normalizeKey(a);
    b = normalizeKey(b);
  
    var ai = collationIndex(a);
    var bi = collationIndex(b);
    if ((ai - bi) !== 0) {
      return ai - bi;
    }
    if (a === null) {
      return 0;
    }
    switch (typeof a) {
      case 'number':
        return a - b;
      case 'boolean':
        return a === b ? 0 : (a < b ? -1 : 1);
      case 'string':
        return stringCollate(a, b);
    }
    return Array.isArray(a) ? arrayCollate(a, b) : objectCollate(a, b);
  }
  
  // couch considers null/NaN/Infinity/-Infinity === undefined,
  // for the purposes of mapreduce indexes. also, dates get stringified.
  function normalizeKey(key) {
    switch (typeof key) {
      case 'undefined':
        return null;
      case 'number':
        if (key === Infinity || key === -Infinity || isNaN(key)) {
          return null;
        }
        return key;
      case 'object':
        var origKey = key;
        if (Array.isArray(key)) {
          var len = key.length;
          key = new Array(len);
          for (var i = 0; i < len; i++) {
            key[i] = normalizeKey(origKey[i]);
          }
        /* istanbul ignore next */
        } else if (key instanceof Date) {
          return key.toJSON();
        } else if (key !== null) { // generic object
          key = {};
          for (var k in origKey) {
            if (origKey.hasOwnProperty(k)) {
              var val = origKey[k];
              if (typeof val !== 'undefined') {
                key[k] = normalizeKey(val);
              }
            }
          }
        }
    }
    return key;
  }
  
  function indexify(key) {
    if (key !== null) {
      switch (typeof key) {
        case 'boolean':
          return key ? 1 : 0;
        case 'number':
          return numToIndexableString(key);
        case 'string':
          // We've to be sure that key does not contain \u0000
          // Do order-preserving replacements:
          // 0 -> 1, 1
          // 1 -> 1, 2
          // 2 -> 2, 2
          return key
            .replace(/\u0002/g, '\u0002\u0002')
            .replace(/\u0001/g, '\u0001\u0002')
            .replace(/\u0000/g, '\u0001\u0001');
        case 'object':
          var isArray = Array.isArray(key);
          var arr = isArray ? key : Object.keys(key);
          var i = -1;
          var len = arr.length;
          var result = '';
          if (isArray) {
            while (++i < len) {
              result += toIndexableString(arr[i]);
            }
          } else {
            while (++i < len) {
              var objKey = arr[i];
              result += toIndexableString(objKey) +
                  toIndexableString(key[objKey]);
            }
          }
          return result;
      }
    }
    return '';
  }
  
  // convert the given key to a string that would be appropriate
  // for lexical sorting, e.g. within a database, where the
  // sorting is the same given by the collate() function.
  function toIndexableString(key) {
    var zero = '\u0000';
    key = normalizeKey(key);
    return collationIndex(key) + SEP + indexify(key) + zero;
  }
  
  function parseNumber(str, i) {
    var originalIdx = i;
    var num;
    var zero = str[i] === '1';
    if (zero) {
      num = 0;
      i++;
    } else {
      var neg = str[i] === '0';
      i++;
      var numAsString = '';
      var magAsString = str.substring(i, i + MAGNITUDE_DIGITS);
      var magnitude = parseInt(magAsString, 10) + MIN_MAGNITUDE;
      /* istanbul ignore next */
      if (neg) {
        magnitude = -magnitude;
      }
      i += MAGNITUDE_DIGITS;
      while (true) {
        var ch = str[i];
        if (ch === '\u0000') {
          break;
        } else {
          numAsString += ch;
        }
        i++;
      }
      numAsString = numAsString.split('.');
      if (numAsString.length === 1) {
        num = parseInt(numAsString, 10);
      } else {
        /* istanbul ignore next */
        num = parseFloat(numAsString[0] + '.' + numAsString[1]);
      }
      /* istanbul ignore next */
      if (neg) {
        num = num - 10;
      }
      /* istanbul ignore next */
      if (magnitude !== 0) {
        // parseFloat is more reliable than pow due to rounding errors
        // e.g. Number.MAX_VALUE would return Infinity if we did
        // num * Math.pow(10, magnitude);
        num = parseFloat(num + 'e' + magnitude);
      }
    }
    return {num: num, length : i - originalIdx};
  }
  
  // move up the stack while parsing
  // this function moved outside of parseIndexableString for performance
  function pop(stack, metaStack) {
    var obj = stack.pop();
  
    if (metaStack.length) {
      var lastMetaElement = metaStack[metaStack.length - 1];
      if (obj === lastMetaElement.element) {
        // popping a meta-element, e.g. an object whose value is another object
        metaStack.pop();
        lastMetaElement = metaStack[metaStack.length - 1];
      }
      var element = lastMetaElement.element;
      var lastElementIndex = lastMetaElement.index;
      if (Array.isArray(element)) {
        element.push(obj);
      } else if (lastElementIndex === stack.length - 2) { // obj with key+value
        var key = stack.pop();
        element[key] = obj;
      } else {
        stack.push(obj); // obj with key only
      }
    }
  }
  
  function parseIndexableString(str) {
    var stack = [];
    var metaStack = []; // stack for arrays and objects
    var i = 0;
  
    /*eslint no-constant-condition: ["error", { "checkLoops": false }]*/
    while (true) {
      var collationIndex = str[i++];
      if (collationIndex === '\u0000') {
        if (stack.length === 1) {
          return stack.pop();
        } else {
          pop(stack, metaStack);
          continue;
        }
      }
      switch (collationIndex) {
        case '1':
          stack.push(null);
          break;
        case '2':
          stack.push(str[i] === '1');
          i++;
          break;
        case '3':
          var parsedNum = parseNumber(str, i);
          stack.push(parsedNum.num);
          i += parsedNum.length;
          break;
        case '4':
          var parsedStr = '';
          /*eslint no-constant-condition: ["error", { "checkLoops": false }]*/
          while (true) {
            var ch = str[i];
            if (ch === '\u0000') {
              break;
            }
            parsedStr += ch;
            i++;
          }
          // perform the reverse of the order-preserving replacement
          // algorithm (see above)
          parsedStr = parsedStr.replace(/\u0001\u0001/g, '\u0000')
            .replace(/\u0001\u0002/g, '\u0001')
            .replace(/\u0002\u0002/g, '\u0002');
          stack.push(parsedStr);
          break;
        case '5':
          var arrayElement = { element: [], index: stack.length };
          stack.push(arrayElement.element);
          metaStack.push(arrayElement);
          break;
        case '6':
          var objElement = { element: {}, index: stack.length };
          stack.push(objElement.element);
          metaStack.push(objElement);
          break;
        /* istanbul ignore next */
        default:
          throw new Error(
            'bad collationIndex or unexpectedly reached end of input: ' +
              collationIndex);
      }
    }
  }
  
  function arrayCollate(a, b) {
    var len = Math.min(a.length, b.length);
    for (var i = 0; i < len; i++) {
      var sort = collate(a[i], b[i]);
      if (sort !== 0) {
        return sort;
      }
    }
    return (a.length === b.length) ? 0 :
      (a.length > b.length) ? 1 : -1;
  }
  function stringCollate(a, b) {
    // See: https://github.com/daleharvey/pouchdb/issues/40
    // This is incompatible with the CouchDB implementation, but its the
    // best we can do for now
    return (a === b) ? 0 : ((a > b) ? 1 : -1);
  }
  function objectCollate(a, b) {
    var ak = Object.keys(a), bk = Object.keys(b);
    var len = Math.min(ak.length, bk.length);
    for (var i = 0; i < len; i++) {
      // First sort the keys
      var sort = collate(ak[i], bk[i]);
      if (sort !== 0) {
        return sort;
      }
      // if the keys are equal sort the values
      sort = collate(a[ak[i]], b[bk[i]]);
      if (sort !== 0) {
        return sort;
      }
  
    }
    return (ak.length === bk.length) ? 0 :
      (ak.length > bk.length) ? 1 : -1;
  }
  // The collation is defined by erlangs ordered terms
  // the atoms null, true, false come first, then numbers, strings,
  // arrays, then objects
  // null/undefined/NaN/Infinity/-Infinity are all considered null
  function collationIndex(x) {
    var id = ['boolean', 'number', 'string', 'object'];
    var idx = id.indexOf(typeof x);
    //false if -1 otherwise true, but fast!!!!1
    if (~idx) {
      if (x === null) {
        return 1;
      }
      if (Array.isArray(x)) {
        return 5;
      }
      return idx < 3 ? (idx + 2) : (idx + 3);
    }
    /* istanbul ignore next */
    if (Array.isArray(x)) {
      return 5;
    }
  }
  
  // conversion:
  // x yyy zz...zz
  // x = 0 for negative, 1 for 0, 2 for positive
  // y = exponent (for negative numbers negated) moved so that it's >= 0
  // z = mantisse
  function numToIndexableString(num) {
  
    if (num === 0) {
      return '1';
    }
  
    // convert number to exponential format for easier and
    // more succinct string sorting
    var expFormat = num.toExponential().split(/e\+?/);
    var magnitude = parseInt(expFormat[1], 10);
  
    var neg = num < 0;
  
    var result = neg ? '0' : '2';
  
    // first sort by magnitude
    // it's easier if all magnitudes are positive
    var magForComparison = ((neg ? -magnitude : magnitude) - MIN_MAGNITUDE);
    var magString = padLeft((magForComparison).toString(), '0', MAGNITUDE_DIGITS);
  
    result += SEP + magString;
  
    // then sort by the factor
    var factor = Math.abs(parseFloat(expFormat[0])); // [1..10)
    /* istanbul ignore next */
    if (neg) { // for negative reverse ordering
      factor = 10 - factor;
    }
  
    var factorStr = factor.toFixed(20);
  
    // strip zeros from the end
    factorStr = factorStr.replace(/\.?0+$/, '');
  
    result += SEP + factorStr;
  
    return result;
  }
  
  /*
   * Simple task queue to sequentialize actions. Assumes
   * callbacks will eventually fire (once).
   */
  
  function TaskQueue$1() {
    this.promise = new PouchPromise(function (fulfill) {fulfill(); });
  }
  TaskQueue$1.prototype.add = function (promiseFactory) {
    this.promise = this.promise["catch"](function () {
      // just recover
    }).then(function () {
      return promiseFactory();
    });
    return this.promise;
  };
  TaskQueue$1.prototype.finish = function () {
    return this.promise;
  };
  
  function createView(opts) {
    var sourceDB = opts.db;
    var viewName = opts.viewName;
    var mapFun = opts.map;
    var reduceFun = opts.reduce;
    var temporary = opts.temporary;
  
    // the "undefined" part is for backwards compatibility
    var viewSignature = mapFun.toString() + (reduceFun && reduceFun.toString()) +
      'undefined';
  
    var cachedViews;
    if (!temporary) {
      // cache this to ensure we don't try to update the same view twice
      cachedViews = sourceDB._cachedViews = sourceDB._cachedViews || {};
      if (cachedViews[viewSignature]) {
        return cachedViews[viewSignature];
      }
    }
  
    var promiseForView = sourceDB.info().then(function (info) {
  
      var depDbName = info.db_name + '-mrview-' +
        (temporary ? 'temp' : stringMd5(viewSignature));
  
      // save the view name in the source db so it can be cleaned up if necessary
      // (e.g. when the _design doc is deleted, remove all associated view data)
      function diffFunction(doc) {
        doc.views = doc.views || {};
        var fullViewName = viewName;
        if (fullViewName.indexOf('/') === -1) {
          fullViewName = viewName + '/' + viewName;
        }
        var depDbs = doc.views[fullViewName] = doc.views[fullViewName] || {};
        /* istanbul ignore if */
        if (depDbs[depDbName]) {
          return; // no update necessary
        }
        depDbs[depDbName] = true;
        return doc;
      }
      return upsert(sourceDB, '_local/mrviews', diffFunction).then(function () {
        return sourceDB.registerDependentDatabase(depDbName).then(function (res) {
          var db = res.db;
          db.auto_compaction = true;
          var view = {
            name: depDbName,
            db: db,
            sourceDB: sourceDB,
            adapter: sourceDB.adapter,
            mapFun: mapFun,
            reduceFun: reduceFun
          };
          return view.db.get('_local/lastSeq')["catch"](function (err) {
            /* istanbul ignore if */
            if (err.status !== 404) {
              throw err;
            }
          }).then(function (lastSeqDoc) {
            view.seq = lastSeqDoc ? lastSeqDoc.seq : 0;
            if (cachedViews) {
              view.db.once('destroyed', function () {
                delete cachedViews[viewSignature];
              });
            }
            return view;
          });
        });
      });
    });
  
    if (cachedViews) {
      cachedViews[viewSignature] = promiseForView;
    }
    return promiseForView;
  }
  
  function QueryParseError(message) {
    this.status = 400;
    this.name = 'query_parse_error';
    this.message = message;
    this.error = true;
    try {
      Error.captureStackTrace(this, QueryParseError);
    } catch (e) {}
  }
  
  inherits(QueryParseError, Error);
  
  function NotFoundError(message) {
    this.status = 404;
    this.name = 'not_found';
    this.message = message;
    this.error = true;
    try {
      Error.captureStackTrace(this, NotFoundError);
    } catch (e) {}
  }
  
  inherits(NotFoundError, Error);
  
  function BuiltInError(message) {
    this.status = 500;
    this.name = 'invalid_value';
    this.message = message;
    this.error = true;
    try {
      Error.captureStackTrace(this, BuiltInError);
    } catch (e) {}
  }
  
  inherits(BuiltInError, Error);
  
  function createBuiltInError(name) {
    var message = 'builtin ' + name +
      ' function requires map values to be numbers' +
      ' or number arrays';
    return new BuiltInError(message);
  }
  
  function sum(values) {
    var result = 0;
    for (var i = 0, len = values.length; i < len; i++) {
      var num = values[i];
      if (typeof num !== 'number') {
        if (Array.isArray(num)) {
          // lists of numbers are also allowed, sum them separately
          result = typeof result === 'number' ? [result] : result;
          for (var j = 0, jLen = num.length; j < jLen; j++) {
            var jNum = num[j];
            if (typeof jNum !== 'number') {
              throw createBuiltInError('_sum');
            } else if (typeof result[j] === 'undefined') {
              result.push(jNum);
            } else {
              result[j] += jNum;
            }
          }
        } else { // not array/number
          throw createBuiltInError('_sum');
        }
      } else if (typeof result === 'number') {
        result += num;
      } else { // add number to array
        result[0] += num;
      }
    }
    return result;
  }
  
  var log$2 = guardedConsole.bind(null, 'log');
  var isArray = Array.isArray;
  var toJSON = JSON.parse;
  
  function evalFunctionWithEval(func, emit) {
    return scopedEval(
      "return (" + func.replace(/;\s*$/, "") + ");",
      {
        emit: emit,
        sum: sum,
        log: log$2,
        isArray: isArray,
        toJSON: toJSON
      }
    );
  }
  
  var promisedCallback = function (promise, callback) {
    if (callback) {
      promise.then(function (res) {
        process.nextTick(function () {
          callback(null, res);
        });
      }, function (reason) {
        process.nextTick(function () {
          callback(reason);
        });
      });
    }
    return promise;
  };
  
  var callbackify = function (fun) {
    return getArguments(function (args) {
      var cb = args.pop();
      var promise = fun.apply(this, args);
      if (typeof cb === 'function') {
        promisedCallback(promise, cb);
      }
      return promise;
    });
  };
  
  // Promise finally util similar to Q.finally
  var fin = function (promise, finalPromiseFactory) {
    return promise.then(function (res) {
      return finalPromiseFactory().then(function () {
        return res;
      });
    }, function (reason) {
      return finalPromiseFactory().then(function () {
        throw reason;
      });
    });
  };
  
  var sequentialize = function (queue, promiseFactory) {
    return function () {
      var args = arguments;
      var that = this;
      return queue.add(function () {
        return promiseFactory.apply(that, args);
      });
    };
  };
  
  // uniq an array of strings, order not guaranteed
  // similar to underscore/lodash _.uniq
  var uniq = function (arr) {
    var map = {};
  
    for (var i = 0, len = arr.length; i < len; i++) {
      map['$' + arr[i]] = true;
    }
  
    var keys = Object.keys(map);
    var output = new Array(keys.length);
  
    for (i = 0, len = keys.length; i < len; i++) {
      output[i] = keys[i].substring(1);
    }
    return output;
  };
  
  var persistentQueues = {};
  var tempViewQueue = new TaskQueue$1();
  var CHANGES_BATCH_SIZE$1 = 50;
  
  function parseViewName(name) {
    // can be either 'ddocname/viewname' or just 'viewname'
    // (where the ddoc name is the same)
    return name.indexOf('/') === -1 ? [name, name] : name.split('/');
  }
  
  function isGenOne(changes) {
    // only return true if the current change is 1-
    // and there are no other leafs
    return changes.length === 1 && /^1-/.test(changes[0].rev);
  }
  
  function emitError(db, e) {
    try {
      db.emit('error', e);
    } catch (err) {
      guardedConsole('error',
        'The user\'s map/reduce function threw an uncaught error.\n' +
        'You can debug this error by doing:\n' +
        'myDatabase.on(\'error\', function (err) { debugger; });\n' +
        'Please double-check your map/reduce function.');
      guardedConsole('error', e);
    }
  }
  
  function tryCode$1(db, fun, args) {
    // emit an event if there was an error thrown by a map/reduce function.
    // putting try/catches in a single function also avoids deoptimizations.
    try {
      return {
        output : fun.apply(null, args)
      };
    } catch (e) {
      emitError(db, e);
      return {error: e};
    }
  }
  
  function sortByKeyThenValue(x, y) {
    var keyCompare = collate(x.key, y.key);
    return keyCompare !== 0 ? keyCompare : collate(x.value, y.value);
  }
  
  function sliceResults(results, limit, skip) {
    skip = skip || 0;
    if (typeof limit === 'number') {
      return results.slice(skip, limit + skip);
    } else if (skip > 0) {
      return results.slice(skip);
    }
    return results;
  }
  
  function rowToDocId(row) {
    var val = row.value;
    // Users can explicitly specify a joined doc _id, or it
    // defaults to the doc _id that emitted the key/value.
    var docId = (val && typeof val === 'object' && val._id) || row.id;
    return docId;
  }
  
  function readAttachmentsAsBlobOrBuffer$1(res) {
    res.rows.forEach(function (row) {
      var atts = row.doc && row.doc._attachments;
      if (!atts) {
        return;
      }
      Object.keys(atts).forEach(function (filename) {
        var att = atts[filename];
        atts[filename].data = b64ToBluffer(att.data, att.content_type);
      });
    });
  }
  
  function postprocessAttachments(opts) {
    return function (res) {
      if (opts.include_docs && opts.attachments && opts.binary) {
        readAttachmentsAsBlobOrBuffer$1(res);
      }
      return res;
    };
  }
  
  var builtInReduce = {
    _sum: function (keys, values) {
      return sum(values);
    },
  
    _count: function (keys, values) {
      return values.length;
    },
  
    _stats: function (keys, values) {
      // no need to implement rereduce=true, because Pouch
      // will never call it
      function sumsqr(values) {
        var _sumsqr = 0;
        for (var i = 0, len = values.length; i < len; i++) {
          var num = values[i];
          _sumsqr += (num * num);
        }
        return _sumsqr;
      }
      return {
        sum     : sum(values),
        min     : Math.min.apply(null, values),
        max     : Math.max.apply(null, values),
        count   : values.length,
        sumsqr : sumsqr(values)
      };
    }
  };
  
  function addHttpParam(paramName, opts, params, asJson) {
    // add an http param from opts to params, optionally json-encoded
    var val = opts[paramName];
    if (typeof val !== 'undefined') {
      if (asJson) {
        val = encodeURIComponent(JSON.stringify(val));
      }
      params.push(paramName + '=' + val);
    }
  }
  
  function coerceInteger(integerCandidate) {
    if (typeof integerCandidate !== 'undefined') {
      var asNumber = Number(integerCandidate);
      // prevents e.g. '1foo' or '1.1' being coerced to 1
      if (!isNaN(asNumber) && asNumber === parseInt(integerCandidate, 10)) {
        return asNumber;
      } else {
        return integerCandidate;
      }
    }
  }
  
  function coerceOptions(opts) {
    opts.group_level = coerceInteger(opts.group_level);
    opts.limit = coerceInteger(opts.limit);
    opts.skip = coerceInteger(opts.skip);
    return opts;
  }
  
  function checkPositiveInteger(number) {
    if (number) {
      if (typeof number !== 'number') {
        return  new QueryParseError('Invalid value for integer: "' +
        number + '"');
      }
      if (number < 0) {
        return new QueryParseError('Invalid value for positive integer: ' +
          '"' + number + '"');
      }
    }
  }
  
  function checkQueryParseError(options, fun) {
    var startkeyName = options.descending ? 'endkey' : 'startkey';
    var endkeyName = options.descending ? 'startkey' : 'endkey';
  
    if (typeof options[startkeyName] !== 'undefined' &&
      typeof options[endkeyName] !== 'undefined' &&
      collate(options[startkeyName], options[endkeyName]) > 0) {
      throw new QueryParseError('No rows can match your key range, ' +
      'reverse your start_key and end_key or set {descending : true}');
    } else if (fun.reduce && options.reduce !== false) {
      if (options.include_docs) {
        throw new QueryParseError('{include_docs:true} is invalid for reduce');
      } else if (options.keys && options.keys.length > 1 &&
          !options.group && !options.group_level) {
        throw new QueryParseError('Multi-key fetches for reduce views must use ' +
        '{group: true}');
      }
    }
    ['group_level', 'limit', 'skip'].forEach(function (optionName) {
      var error = checkPositiveInteger(options[optionName]);
      if (error) {
        throw error;
      }
    });
  }
  
  function httpQuery(db, fun, opts) {
    // List of parameters to add to the PUT request
    var params = [];
    var body;
    var method = 'GET';
  
    // If opts.reduce exists and is defined, then add it to the list
    // of parameters.
    // If reduce=false then the results are that of only the map function
    // not the final result of map and reduce.
    addHttpParam('reduce', opts, params);
    addHttpParam('include_docs', opts, params);
    addHttpParam('attachments', opts, params);
    addHttpParam('limit', opts, params);
    addHttpParam('descending', opts, params);
    addHttpParam('group', opts, params);
    addHttpParam('group_level', opts, params);
    addHttpParam('skip', opts, params);
    addHttpParam('stale', opts, params);
    addHttpParam('conflicts', opts, params);
    addHttpParam('startkey', opts, params, true);
    addHttpParam('start_key', opts, params, true);
    addHttpParam('endkey', opts, params, true);
    addHttpParam('end_key', opts, params, true);
    addHttpParam('inclusive_end', opts, params);
    addHttpParam('key', opts, params, true);
  
    // Format the list of parameters into a valid URI query string
    params = params.join('&');
    params = params === '' ? '' : '?' + params;
  
    // If keys are supplied, issue a POST to circumvent GET query string limits
    // see http://wiki.apache.org/couchdb/HTTP_view_API#Querying_Options
    if (typeof opts.keys !== 'undefined') {
      var MAX_URL_LENGTH = 2000;
      // according to http://stackoverflow.com/a/417184/680742,
      // the de facto URL length limit is 2000 characters
  
      var keysAsString =
        'keys=' + encodeURIComponent(JSON.stringify(opts.keys));
      if (keysAsString.length + params.length + 1 <= MAX_URL_LENGTH) {
        // If the keys are short enough, do a GET. we do this to work around
        // Safari not understanding 304s on POSTs (see pouchdb/pouchdb#1239)
        params += (params[0] === '?' ? '&' : '?') + keysAsString;
      } else {
        method = 'POST';
        if (typeof fun === 'string') {
          body = {keys: opts.keys};
        } else { // fun is {map : mapfun}, so append to this
          fun.keys = opts.keys;
        }
      }
    }
  
    // We are referencing a query defined in the design doc
    if (typeof fun === 'string') {
      var parts = parseViewName(fun);
      return db.request({
        method: method,
        url: '_design/' + parts[0] + '/_view/' + parts[1] + params,
        body: body
      }).then(postprocessAttachments(opts));
    }
  
    // We are using a temporary view, terrible for performance, good for testing
    body = body || {};
    Object.keys(fun).forEach(function (key) {
      if (Array.isArray(fun[key])) {
        body[key] = fun[key];
      } else {
        body[key] = fun[key].toString();
      }
    });
    return db.request({
      method: 'POST',
      url: '_temp_view' + params,
      body: body
    }).then(postprocessAttachments(opts));
  }
  
  // custom adapters can define their own api._query
  // and override the default behavior
  /* istanbul ignore next */
  function customQuery(db, fun, opts) {
    return new PouchPromise(function (resolve, reject) {
      db._query(fun, opts, function (err, res) {
        if (err) {
          return reject(err);
        }
        resolve(res);
      });
    });
  }
  
  // custom adapters can define their own api._viewCleanup
  // and override the default behavior
  /* istanbul ignore next */
  function customViewCleanup(db) {
    return new PouchPromise(function (resolve, reject) {
      db._viewCleanup(function (err, res) {
        if (err) {
          return reject(err);
        }
        resolve(res);
      });
    });
  }
  
  function defaultsTo(value) {
    return function (reason) {
      /* istanbul ignore else */
      if (reason.status === 404) {
        return value;
      } else {
        throw reason;
      }
    };
  }
  
  // returns a promise for a list of docs to update, based on the input docId.
  // the order doesn't matter, because post-3.2.0, bulkDocs
  // is an atomic operation in all three adapters.
  function getDocsToPersist(docId, view, docIdsToChangesAndEmits) {
    var metaDocId = '_local/doc_' + docId;
    var defaultMetaDoc = {_id: metaDocId, keys: []};
    var docData = docIdsToChangesAndEmits[docId];
    var indexableKeysToKeyValues = docData.indexableKeysToKeyValues;
    var changes = docData.changes;
  
    function getMetaDoc() {
      if (isGenOne(changes)) {
        // generation 1, so we can safely assume initial state
        // for performance reasons (avoids unnecessary GETs)
        return PouchPromise.resolve(defaultMetaDoc);
      }
      return view.db.get(metaDocId)["catch"](defaultsTo(defaultMetaDoc));
    }
  
    function getKeyValueDocs(metaDoc) {
      if (!metaDoc.keys.length) {
        // no keys, no need for a lookup
        return PouchPromise.resolve({rows: []});
      }
      return view.db.allDocs({
        keys: metaDoc.keys,
        include_docs: true
      });
    }
  
    function processKvDocs(metaDoc, kvDocsRes) {
      var kvDocs = [];
      var oldKeysMap = {};
  
      for (var i = 0, len = kvDocsRes.rows.length; i < len; i++) {
        var row = kvDocsRes.rows[i];
        var doc = row.doc;
        if (!doc) { // deleted
          continue;
        }
        kvDocs.push(doc);
        oldKeysMap[doc._id] = true;
        doc._deleted = !indexableKeysToKeyValues[doc._id];
        if (!doc._deleted) {
          var keyValue = indexableKeysToKeyValues[doc._id];
          if ('value' in keyValue) {
            doc.value = keyValue.value;
          }
        }
      }
  
      var newKeys = Object.keys(indexableKeysToKeyValues);
      newKeys.forEach(function (key) {
        if (!oldKeysMap[key]) {
          // new doc
          var kvDoc = {
            _id: key
          };
          var keyValue = indexableKeysToKeyValues[key];
          if ('value' in keyValue) {
            kvDoc.value = keyValue.value;
          }
          kvDocs.push(kvDoc);
        }
      });
      metaDoc.keys = uniq(newKeys.concat(metaDoc.keys));
      kvDocs.push(metaDoc);
  
      return kvDocs;
    }
  
    return getMetaDoc().then(function (metaDoc) {
      return getKeyValueDocs(metaDoc).then(function (kvDocsRes) {
        return processKvDocs(metaDoc, kvDocsRes);
      });
    });
  }
  
  // updates all emitted key/value docs and metaDocs in the mrview database
  // for the given batch of documents from the source database
  function saveKeyValues(view, docIdsToChangesAndEmits, seq) {
    var seqDocId = '_local/lastSeq';
    return view.db.get(seqDocId)[
    "catch"](defaultsTo({_id: seqDocId, seq: 0}))
    .then(function (lastSeqDoc) {
      var docIds = Object.keys(docIdsToChangesAndEmits);
      return PouchPromise.all(docIds.map(function (docId) {
        return getDocsToPersist(docId, view, docIdsToChangesAndEmits);
      })).then(function (listOfDocsToPersist) {
        var docsToPersist = flatten(listOfDocsToPersist);
        lastSeqDoc.seq = seq;
        docsToPersist.push(lastSeqDoc);
        // write all docs in a single operation, update the seq once
        return view.db.bulkDocs({docs : docsToPersist});
      });
    });
  }
  
  function getQueue(view) {
    var viewName = typeof view === 'string' ? view : view.name;
    var queue = persistentQueues[viewName];
    if (!queue) {
      queue = persistentQueues[viewName] = new TaskQueue$1();
    }
    return queue;
  }
  
  function updateView(view) {
    return sequentialize(getQueue(view), function () {
      return updateViewInQueue(view);
    })();
  }
  
  function updateViewInQueue(view) {
    // bind the emit function once
    var mapResults;
    var doc;
  
    function emit(key, value) {
      var output = {id: doc._id, key: normalizeKey(key)};
      // Don't explicitly store the value unless it's defined and non-null.
      // This saves on storage space, because often people don't use it.
      if (typeof value !== 'undefined' && value !== null) {
        output.value = normalizeKey(value);
      }
      mapResults.push(output);
    }
  
    var mapFun;
    // for temp_views one can use emit(doc, emit), see #38
    if (typeof view.mapFun === "function" && view.mapFun.length === 2) {
      var origMap = view.mapFun;
      mapFun = function (doc) {
        return origMap(doc, emit);
      };
    } else {
      mapFun = evalFunctionWithEval(view.mapFun.toString(), emit);
    }
  
    var currentSeq = view.seq || 0;
  
    function processChange(docIdsToChangesAndEmits, seq) {
      return function () {
        return saveKeyValues(view, docIdsToChangesAndEmits, seq);
      };
    }
  
    var queue = new TaskQueue$1();
    // TODO(neojski): https://github.com/daleharvey/pouchdb/issues/1521
  
    return new PouchPromise(function (resolve, reject) {
  
      function complete() {
        queue.finish().then(function () {
          view.seq = currentSeq;
          resolve();
        });
      }
  
      function processNextBatch() {
        view.sourceDB.changes({
          conflicts: true,
          include_docs: true,
          style: 'all_docs',
          since: currentSeq,
          limit: CHANGES_BATCH_SIZE$1
        }).on('complete', function (response) {
          var results = response.results;
          if (!results.length) {
            return complete();
          }
          var docIdsToChangesAndEmits = {};
          for (var i = 0, l = results.length; i < l; i++) {
            var change = results[i];
            if (change.doc._id[0] !== '_') {
              mapResults = [];
              doc = change.doc;
  
              if (!doc._deleted) {
                tryCode$1(view.sourceDB, mapFun, [doc]);
              }
              mapResults.sort(sortByKeyThenValue);
  
              var indexableKeysToKeyValues = {};
              var lastKey;
              for (var j = 0, jl = mapResults.length; j < jl; j++) {
                var obj = mapResults[j];
                var complexKey = [obj.key, obj.id];
                if (collate(obj.key, lastKey) === 0) {
                  complexKey.push(j); // dup key+id, so make it unique
                }
                var indexableKey = toIndexableString(complexKey);
                indexableKeysToKeyValues[indexableKey] = obj;
                lastKey = obj.key;
              }
              docIdsToChangesAndEmits[change.doc._id] = {
                indexableKeysToKeyValues: indexableKeysToKeyValues,
                changes: change.changes
              };
            }
            currentSeq = change.seq;
          }
          queue.add(processChange(docIdsToChangesAndEmits, currentSeq));
          if (results.length < CHANGES_BATCH_SIZE$1) {
            return complete();
          }
          return processNextBatch();
        }).on('error', onError);
        /* istanbul ignore next */
        function onError(err) {
          reject(err);
        }
      }
  
      processNextBatch();
    });
  }
  
  function reduceView(view, results, options) {
    if (options.group_level === 0) {
      delete options.group_level;
    }
  
    var shouldGroup = options.group || options.group_level;
  
    var reduceFun;
    if (builtInReduce[view.reduceFun]) {
      reduceFun = builtInReduce[view.reduceFun];
    } else {
      reduceFun = evalFunctionWithEval(view.reduceFun.toString());
    }
  
    var groups = [];
    var lvl = isNaN(options.group_level) ? Number.POSITIVE_INFINITY :
      options.group_level;
    results.forEach(function (e) {
      var last = groups[groups.length - 1];
      var groupKey = shouldGroup ? e.key : null;
  
      // only set group_level for array keys
      if (shouldGroup && Array.isArray(groupKey)) {
        groupKey = groupKey.slice(0, lvl);
      }
  
      if (last && collate(last.groupKey, groupKey) === 0) {
        last.keys.push([e.key, e.id]);
        last.values.push(e.value);
        return;
      }
      groups.push({
        keys: [[e.key, e.id]],
        values: [e.value],
        groupKey: groupKey
      });
    });
    results = [];
    for (var i = 0, len = groups.length; i < len; i++) {
      var e = groups[i];
      var reduceTry = tryCode$1(view.sourceDB, reduceFun,
        [e.keys, e.values, false]);
      if (reduceTry.error && reduceTry.error instanceof BuiltInError) {
        // CouchDB returns an error if a built-in errors out
        throw reduceTry.error;
      }
      results.push({
        // CouchDB just sets the value to null if a non-built-in errors out
        value: reduceTry.error ? null : reduceTry.output,
        key: e.groupKey
      });
    }
    // no total_rows/offset when reducing
    return {rows: sliceResults(results, options.limit, options.skip)};
  }
  
  function queryView(view, opts) {
    return sequentialize(getQueue(view), function () {
      return queryViewInQueue(view, opts);
    })();
  }
  
  function queryViewInQueue(view, opts) {
    var totalRows;
    var shouldReduce = view.reduceFun && opts.reduce !== false;
    var skip = opts.skip || 0;
    if (typeof opts.keys !== 'undefined' && !opts.keys.length) {
      // equivalent query
      opts.limit = 0;
      delete opts.keys;
    }
  
    function fetchFromView(viewOpts) {
      viewOpts.include_docs = true;
      return view.db.allDocs(viewOpts).then(function (res) {
        totalRows = res.total_rows;
        return res.rows.map(function (result) {
  
          // implicit migration - in older versions of PouchDB,
          // we explicitly stored the doc as {id: ..., key: ..., value: ...}
          // this is tested in a migration test
          /* istanbul ignore next */
          if ('value' in result.doc && typeof result.doc.value === 'object' &&
              result.doc.value !== null) {
            var keys = Object.keys(result.doc.value).sort();
            // this detection method is not perfect, but it's unlikely the user
            // emitted a value which was an object with these 3 exact keys
            var expectedKeys = ['id', 'key', 'value'];
            if (!(keys < expectedKeys || keys > expectedKeys)) {
              return result.doc.value;
            }
          }
  
          var parsedKeyAndDocId = parseIndexableString(result.doc._id);
          return {
            key: parsedKeyAndDocId[0],
            id: parsedKeyAndDocId[1],
            value: ('value' in result.doc ? result.doc.value : null)
          };
        });
      });
    }
  
    function onMapResultsReady(rows) {
      var finalResults;
      if (shouldReduce) {
        finalResults = reduceView(view, rows, opts);
      } else {
        finalResults = {
          total_rows: totalRows,
          offset: skip,
          rows: rows
        };
      }
      if (opts.include_docs) {
        var docIds = uniq(rows.map(rowToDocId));
  
        return view.sourceDB.allDocs({
          keys: docIds,
          include_docs: true,
          conflicts: opts.conflicts,
          attachments: opts.attachments,
          binary: opts.binary
        }).then(function (allDocsRes) {
          var docIdsToDocs = {};
          allDocsRes.rows.forEach(function (row) {
            if (row.doc) {
              docIdsToDocs['$' + row.id] = row.doc;
            }
          });
          rows.forEach(function (row) {
            var docId = rowToDocId(row);
            var doc = docIdsToDocs['$' + docId];
            if (doc) {
              row.doc = doc;
            }
          });
          return finalResults;
        });
      } else {
        return finalResults;
      }
    }
  
    if (typeof opts.keys !== 'undefined') {
      var keys = opts.keys;
      var fetchPromises = keys.map(function (key) {
        var viewOpts = {
          startkey : toIndexableString([key]),
          endkey   : toIndexableString([key, {}])
        };
        return fetchFromView(viewOpts);
      });
      return PouchPromise.all(fetchPromises).then(flatten).then(onMapResultsReady);
    } else { // normal query, no 'keys'
      var viewOpts = {
        descending : opts.descending
      };
      if (opts.start_key) {
          opts.startkey = opts.start_key;
      }
      if (opts.end_key) {
          opts.endkey = opts.end_key;
      }
      if (typeof opts.startkey !== 'undefined') {
        viewOpts.startkey = opts.descending ?
          toIndexableString([opts.startkey, {}]) :
          toIndexableString([opts.startkey]);
      }
      if (typeof opts.endkey !== 'undefined') {
        var inclusiveEnd = opts.inclusive_end !== false;
        if (opts.descending) {
          inclusiveEnd = !inclusiveEnd;
        }
  
        viewOpts.endkey = toIndexableString(
          inclusiveEnd ? [opts.endkey, {}] : [opts.endkey]);
      }
      if (typeof opts.key !== 'undefined') {
        var keyStart = toIndexableString([opts.key]);
        var keyEnd = toIndexableString([opts.key, {}]);
        if (viewOpts.descending) {
          viewOpts.endkey = keyStart;
          viewOpts.startkey = keyEnd;
        } else {
          viewOpts.startkey = keyStart;
          viewOpts.endkey = keyEnd;
        }
      }
      if (!shouldReduce) {
        if (typeof opts.limit === 'number') {
          viewOpts.limit = opts.limit;
        }
        viewOpts.skip = skip;
      }
      return fetchFromView(viewOpts).then(onMapResultsReady);
    }
  }
  
  function httpViewCleanup(db) {
    return db.request({
      method: 'POST',
      url: '_view_cleanup'
    });
  }
  
  function localViewCleanup(db) {
    return db.get('_local/mrviews').then(function (metaDoc) {
      var docsToViews = {};
      Object.keys(metaDoc.views).forEach(function (fullViewName) {
        var parts = parseViewName(fullViewName);
        var designDocName = '_design/' + parts[0];
        var viewName = parts[1];
        docsToViews[designDocName] = docsToViews[designDocName] || {};
        docsToViews[designDocName][viewName] = true;
      });
      var opts = {
        keys : Object.keys(docsToViews),
        include_docs : true
      };
      return db.allDocs(opts).then(function (res) {
        var viewsToStatus = {};
        res.rows.forEach(function (row) {
          var ddocName = row.key.substring(8);
          Object.keys(docsToViews[row.key]).forEach(function (viewName) {
            var fullViewName = ddocName + '/' + viewName;
            /* istanbul ignore if */
            if (!metaDoc.views[fullViewName]) {
              // new format, without slashes, to support PouchDB 2.2.0
              // migration test in pouchdb's browser.migration.js verifies this
              fullViewName = viewName;
            }
            var viewDBNames = Object.keys(metaDoc.views[fullViewName]);
            // design doc deleted, or view function nonexistent
            var statusIsGood = row.doc && row.doc.views &&
              row.doc.views[viewName];
            viewDBNames.forEach(function (viewDBName) {
              viewsToStatus[viewDBName] =
                viewsToStatus[viewDBName] || statusIsGood;
            });
          });
        });
        var dbsToDelete = Object.keys(viewsToStatus).filter(
          function (viewDBName) { return !viewsToStatus[viewDBName]; });
        var destroyPromises = dbsToDelete.map(function (viewDBName) {
          return sequentialize(getQueue(viewDBName), function () {
            return new db.constructor(viewDBName, db.__opts).destroy();
          })();
        });
        return PouchPromise.all(destroyPromises).then(function () {
          return {ok: true};
        });
      });
    }, defaultsTo({ok: true}));
  }
  
  var viewCleanup = callbackify(function () {
    var db = this;
    if (db.type() === 'http') {
      return httpViewCleanup(db);
    }
    /* istanbul ignore next */
    if (typeof db._viewCleanup === 'function') {
      return customViewCleanup(db);
    }
    return localViewCleanup(db);
  });
  
  function queryPromised(db, fun, opts) {
    if (db.type() === 'http') {
      return httpQuery(db, fun, opts);
    }
  
    /* istanbul ignore next */
    if (typeof db._query === 'function') {
      return customQuery(db, fun, opts);
    }
  
    if (typeof fun !== 'string') {
      // temp_view
      checkQueryParseError(opts, fun);
  
      var createViewOpts = {
        db : db,
        viewName : 'temp_view/temp_view',
        map : fun.map,
        reduce : fun.reduce,
        temporary : true
      };
      tempViewQueue.add(function () {
        return createView(createViewOpts).then(function (view) {
          function cleanup() {
            return view.db.destroy();
          }
          return fin(updateView(view).then(function () {
            return queryView(view, opts);
          }), cleanup);
        });
      });
      return tempViewQueue.finish();
    } else {
      // persistent view
      var fullViewName = fun;
      var parts = parseViewName(fullViewName);
      var designDocName = parts[0];
      var viewName = parts[1];
      return db.get('_design/' + designDocName).then(function (doc) {
        var fun = doc.views && doc.views[viewName];
  
        if (!fun || typeof fun.map !== 'string') {
          throw new NotFoundError('ddoc ' + designDocName +
          ' has no view named ' + viewName);
        }
        checkQueryParseError(opts, fun);
  
        var createViewOpts = {
          db : db,
          viewName : fullViewName,
          map : fun.map,
          reduce : fun.reduce
        };
        return createView(createViewOpts).then(function (view) {
          if (opts.stale === 'ok' || opts.stale === 'update_after') {
            if (opts.stale === 'update_after') {
              process.nextTick(function () {
                updateView(view);
              });
            }
            return queryView(view, opts);
          } else { // stale not ok
            return updateView(view).then(function () {
              return queryView(view, opts);
            });
          }
        });
      });
    }
  }
  
  var query = function (fun, opts, callback) {
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
    opts = opts ? coerceOptions(opts) : {};
  
    if (typeof fun === 'function') {
      fun = {map : fun};
    }
  
    var db = this;
    var promise = PouchPromise.resolve().then(function () {
      return queryPromised(db, fun, opts);
    });
    promisedCallback(promise, callback);
    return promise;
  };
  
  
  var mapreduce = {
    query: query,
    viewCleanup: viewCleanup
  };
  
  function isGenOne$1(rev) {
    return /^1-/.test(rev);
  }
  
  function fileHasChanged(localDoc, remoteDoc, filename) {
    return !localDoc._attachments ||
           !localDoc._attachments[filename] ||
           localDoc._attachments[filename].digest !== remoteDoc._attachments[filename].digest;
  }
  
  function getDocAttachments(db, doc) {
    var filenames = Object.keys(doc._attachments);
    return PouchPromise.all(filenames.map(function (filename) {
      return db.getAttachment(doc._id, filename, {rev: doc._rev});
    }));
  }
  
  function getDocAttachmentsFromTargetOrSource(target, src, doc) {
    var doCheckForLocalAttachments = src.type() === 'http' && target.type() !== 'http';
    var filenames = Object.keys(doc._attachments);
  
    if (!doCheckForLocalAttachments) {
      return getDocAttachments(src, doc);
    }
  
    return target.get(doc._id).then(function (localDoc) {
      return PouchPromise.all(filenames.map(function (filename) {
        if (fileHasChanged(localDoc, doc, filename)) {
          return src.getAttachment(doc._id, filename);
        }
  
        return target.getAttachment(localDoc._id, filename);
      }));
    })["catch"](function (error) {
      /* istanbul ignore if */
      if (error.status !== 404) {
        throw error;
      }
  
      return getDocAttachments(src, doc);
    });
  }
  
  function createBulkGetOpts(diffs) {
    var requests = [];
    Object.keys(diffs).forEach(function (id) {
      var missingRevs = diffs[id].missing;
      missingRevs.forEach(function (missingRev) {
        requests.push({
          id: id,
          rev: missingRev
        });
      });
    });
  
    return {
      docs: requests,
      revs: true
    };
  }
  
  //
  // Fetch all the documents from the src as described in the "diffs",
  // which is a mapping of docs IDs to revisions. If the state ever
  // changes to "cancelled", then the returned promise will be rejected.
  // Else it will be resolved with a list of fetched documents.
  //
  function getDocs(src, target, diffs, state) {
    diffs = clone(diffs); // we do not need to modify this
  
    var resultDocs = [],
        ok = true;
  
    function getAllDocs() {
  
      var bulkGetOpts = createBulkGetOpts(diffs);
  
      if (!bulkGetOpts.docs.length) { // optimization: skip empty requests
        return;
      }
  
      return src.bulkGet(bulkGetOpts).then(function (bulkGetResponse) {
        /* istanbul ignore if */
        if (state.cancelled) {
          throw new Error('cancelled');
        }
        return PouchPromise.all(bulkGetResponse.results.map(function (bulkGetInfo) {
          return PouchPromise.all(bulkGetInfo.docs.map(function (doc) {
            var remoteDoc = doc.ok;
  
            if (doc.error) {
              // when AUTO_COMPACTION is set, docs can be returned which look
              // like this: {"missing":"1-7c3ac256b693c462af8442f992b83696"}
              ok = false;
            }
  
            if (!remoteDoc || !remoteDoc._attachments) {
              return remoteDoc;
            }
  
            return getDocAttachmentsFromTargetOrSource(target, src, remoteDoc).then(function (attachments) {
              var filenames = Object.keys(remoteDoc._attachments);
              attachments.forEach(function (attachment, i) {
                var att = remoteDoc._attachments[filenames[i]];
                delete att.stub;
                delete att.length;
                att.data = attachment;
              });
  
              return remoteDoc;
            });
          }));
        }))
  
        .then(function (results) {
          resultDocs = resultDocs.concat(flatten(results).filter(Boolean));
        });
      });
    }
  
    function hasAttachments(doc) {
      return doc._attachments && Object.keys(doc._attachments).length > 0;
    }
  
    function fetchRevisionOneDocs(ids) {
      // Optimization: fetch gen-1 docs and attachments in
      // a single request using _all_docs
      return src.allDocs({
        keys: ids,
        include_docs: true
      }).then(function (res) {
        if (state.cancelled) {
          throw new Error('cancelled');
        }
        res.rows.forEach(function (row) {
          if (row.deleted || !row.doc || !isGenOne$1(row.value.rev) ||
              hasAttachments(row.doc)) {
            // if any of these conditions apply, we need to fetch using get()
            return;
          }
  
          // the doc we got back from allDocs() is sufficient
          resultDocs.push(row.doc);
          delete diffs[row.id];
        });
      });
    }
  
    function getRevisionOneDocs() {
      // filter out the generation 1 docs and get them
      // leaving the non-generation one docs to be got otherwise
      var ids = Object.keys(diffs).filter(function (id) {
        var missing = diffs[id].missing;
        return missing.length === 1 && isGenOne$1(missing[0]);
      });
      if (ids.length > 0) {
        return fetchRevisionOneDocs(ids);
      }
    }
  
    function returnResult() {
      return { ok:ok, docs:resultDocs };
    }
  
    return PouchPromise.resolve()
      .then(getRevisionOneDocs)
      .then(getAllDocs)
      .then(returnResult);
  }
  
  var CHECKPOINT_VERSION = 1;
  var REPLICATOR = "pouchdb";
  // This is an arbitrary number to limit the
  // amount of replication history we save in the checkpoint.
  // If we save too much, the checkpoing docs will become very big,
  // if we save fewer, we'll run a greater risk of having to
  // read all the changes from 0 when checkpoint PUTs fail
  // CouchDB 2.0 has a more involved history pruning,
  // but let's go for the simple version for now.
  var CHECKPOINT_HISTORY_SIZE = 5;
  var LOWEST_SEQ = 0;
  
  function updateCheckpoint(db, id, checkpoint, session, returnValue) {
    return db.get(id)["catch"](function (err) {
      if (err.status === 404) {
        if (db.type() === 'http') {
          explainError(
            404, 'PouchDB is just checking if a remote checkpoint exists.'
          );
        }
        return {
          session_id: session,
          _id: id,
          history: [],
          replicator: REPLICATOR,
          version: CHECKPOINT_VERSION
        };
      }
      throw err;
    }).then(function (doc) {
      if (returnValue.cancelled) {
        return;
      }
  
      // if the checkpoint has not changed, do not update
      if (doc.last_seq === checkpoint) {
        return;
      }
  
      // Filter out current entry for this replication
      doc.history = (doc.history || []).filter(function (item) {
        return item.session_id !== session;
      });
  
      // Add the latest checkpoint to history
      doc.history.unshift({
        last_seq: checkpoint,
        session_id: session
      });
  
      // Just take the last pieces in history, to
      // avoid really big checkpoint docs.
      // see comment on history size above
      doc.history = doc.history.slice(0, CHECKPOINT_HISTORY_SIZE);
  
      doc.version = CHECKPOINT_VERSION;
      doc.replicator = REPLICATOR;
  
      doc.session_id = session;
      doc.last_seq = checkpoint;
  
      return db.put(doc)["catch"](function (err) {
        if (err.status === 409) {
          // retry; someone is trying to write a checkpoint simultaneously
          return updateCheckpoint(db, id, checkpoint, session, returnValue);
        }
        throw err;
      });
    });
  }
  
  function Checkpointer(src, target, id, returnValue) {
    this.src = src;
    this.target = target;
    this.id = id;
    this.returnValue = returnValue;
  }
  
  Checkpointer.prototype.writeCheckpoint = function (checkpoint, session) {
    var self = this;
    return this.updateTarget(checkpoint, session).then(function () {
      return self.updateSource(checkpoint, session);
    });
  };
  
  Checkpointer.prototype.updateTarget = function (checkpoint, session) {
    return updateCheckpoint(this.target, this.id, checkpoint,
      session, this.returnValue);
  };
  
  Checkpointer.prototype.updateSource = function (checkpoint, session) {
    var self = this;
    if (this.readOnlySource) {
      return PouchPromise.resolve(true);
    }
    return updateCheckpoint(this.src, this.id, checkpoint,
      session, this.returnValue)[
      "catch"](function (err) {
        if (isForbiddenError(err)) {
          self.readOnlySource = true;
          return true;
        }
        throw err;
      });
  };
  
  var comparisons = {
    "undefined": function (targetDoc, sourceDoc) {
      // This is the previous comparison function
      if (collate(targetDoc.last_seq, sourceDoc.last_seq) === 0) {
        return sourceDoc.last_seq;
      }
      /* istanbul ignore next */
      return 0;
    },
    "1": function (targetDoc, sourceDoc) {
      // This is the comparison function ported from CouchDB
      return compareReplicationLogs(sourceDoc, targetDoc).last_seq;
    }
  };
  
  Checkpointer.prototype.getCheckpoint = function () {
    var self = this;
    return self.target.get(self.id).then(function (targetDoc) {
      if (self.readOnlySource) {
        return PouchPromise.resolve(targetDoc.last_seq);
      }
  
      return self.src.get(self.id).then(function (sourceDoc) {
        // Since we can't migrate an old version doc to a new one
        // (no session id), we just go with the lowest seq in this case
        /* istanbul ignore if */
        if (targetDoc.version !== sourceDoc.version) {
          return LOWEST_SEQ;
        }
  
        var version;
        if (targetDoc.version) {
          version = targetDoc.version.toString();
        } else {
          version = "undefined";
        }
  
        if (version in comparisons) {
          return comparisons[version](targetDoc, sourceDoc);
        }
        /* istanbul ignore next */
        return LOWEST_SEQ;
      }, function (err) {
        if (err.status === 404 && targetDoc.last_seq) {
          return self.src.put({
            _id: self.id,
            last_seq: LOWEST_SEQ
          }).then(function () {
            return LOWEST_SEQ;
          }, function (err) {
            if (isForbiddenError(err)) {
              self.readOnlySource = true;
              return targetDoc.last_seq;
            }
            /* istanbul ignore next */
            return LOWEST_SEQ;
          });
        }
        throw err;
      });
    })["catch"](function (err) {
      if (err.status !== 404) {
        throw err;
      }
      return LOWEST_SEQ;
    });
  };
  // This checkpoint comparison is ported from CouchDBs source
  // they come from here:
  // https://github.com/apache/couchdb-couch-replicator/blob/master/src/couch_replicator.erl#L863-L906
  
  function compareReplicationLogs(srcDoc, tgtDoc) {
    if (srcDoc.session_id === tgtDoc.session_id) {
      return {
        last_seq: srcDoc.last_seq,
        history: srcDoc.history
      };
    }
  
    return compareReplicationHistory(srcDoc.history, tgtDoc.history);
  }
  
  function compareReplicationHistory(sourceHistory, targetHistory) {
    // the erlang loop via function arguments is not so easy to repeat in JS
    // therefore, doing this as recursion
    var S = sourceHistory[0];
    var sourceRest = sourceHistory.slice(1);
    var T = targetHistory[0];
    var targetRest = targetHistory.slice(1);
  
    if (!S || targetHistory.length === 0) {
      return {
        last_seq: LOWEST_SEQ,
        history: []
      };
    }
  
    var sourceId = S.session_id;
    /* istanbul ignore if */
    if (hasSessionId(sourceId, targetHistory)) {
      return {
        last_seq: S.last_seq,
        history: sourceHistory
      };
    }
  
    var targetId = T.session_id;
    if (hasSessionId(targetId, sourceRest)) {
      return {
        last_seq: T.last_seq,
        history: targetRest
      };
    }
  
    return compareReplicationHistory(sourceRest, targetRest);
  }
  
  function hasSessionId(sessionId, history) {
    var props = history[0];
    var rest = history.slice(1);
  
    if (!sessionId || history.length === 0) {
      return false;
    }
  
    if (sessionId === props.session_id) {
      return true;
    }
  
    return hasSessionId(sessionId, rest);
  }
  
  function isForbiddenError(err) {
    return typeof err.status === 'number' && Math.floor(err.status / 100) === 4;
  }
  
  var STARTING_BACK_OFF = 0;
  
  function backOff(opts, returnValue, error, callback) {
    if (opts.retry === false) {
      returnValue.emit('error', error);
      returnValue.removeAllListeners();
      return;
    }
    if (typeof opts.back_off_function !== 'function') {
      opts.back_off_function = defaultBackOff;
    }
    returnValue.emit('requestError', error);
    if (returnValue.state === 'active' || returnValue.state === 'pending') {
      returnValue.emit('paused', error);
      returnValue.state = 'stopped';
      var backOffSet = function backoffTimeSet() {
        opts.current_back_off = STARTING_BACK_OFF;
      };
      var removeBackOffSetter = function removeBackOffTimeSet() {
        returnValue.removeListener('active', backOffSet);
      };
      returnValue.once('paused', removeBackOffSetter);
      returnValue.once('active', backOffSet);
    }
  
    opts.current_back_off = opts.current_back_off || STARTING_BACK_OFF;
    opts.current_back_off = opts.back_off_function(opts.current_back_off);
    setTimeout(callback, opts.current_back_off);
  }
  
  function sortObjectPropertiesByKey(queryParams) {
    return Object.keys(queryParams).sort(collate).reduce(function (result, key) {
      result[key] = queryParams[key];
      return result;
    }, {});
  }
  
  // Generate a unique id particular to this replication.
  // Not guaranteed to align perfectly with CouchDB's rep ids.
  function generateReplicationId(src, target, opts) {
    var docIds = opts.doc_ids ? opts.doc_ids.sort(collate) : '';
    var filterFun = opts.filter ? opts.filter.toString() : '';
    var queryParams = '';
    var filterViewName =  '';
  
    if (opts.filter && opts.query_params) {
      queryParams = JSON.stringify(sortObjectPropertiesByKey(opts.query_params));
    }
  
    if (opts.filter && opts.filter === '_view') {
      filterViewName = opts.view.toString();
    }
  
    return PouchPromise.all([src.id(), target.id()]).then(function (res) {
      var queryData = res[0] + res[1] + filterFun + filterViewName +
        queryParams + docIds;
      return new PouchPromise(function (resolve) {
        binaryMd5(queryData, resolve);
      });
    }).then(function (md5sum) {
      // can't use straight-up md5 alphabet, because
      // the char '/' is interpreted as being for attachments,
      // and + is also not url-safe
      md5sum = md5sum.replace(/\//g, '.').replace(/\+/g, '_');
      return '_local/' + md5sum;
    });
  }
  
  function replicate$1(src, target, opts, returnValue, result) {
    var batches = [];               // list of batches to be processed
    var currentBatch;               // the batch currently being processed
    var pendingBatch = {
      seq: 0,
      changes: [],
      docs: []
    }; // next batch, not yet ready to be processed
    var writingCheckpoint = false;  // true while checkpoint is being written
    var changesCompleted = false;   // true when all changes received
    var replicationCompleted = false; // true when replication has completed
    var last_seq = 0;
    var continuous = opts.continuous || opts.live || false;
    var batch_size = opts.batch_size || 100;
    var batches_limit = opts.batches_limit || 10;
    var changesPending = false;     // true while src.changes is running
    var doc_ids = opts.doc_ids;
    var repId;
    var checkpointer;
    var changedDocs = [];
    // Like couchdb, every replication gets a unique session id
    var session = uuid();
  
    result = result || {
      ok: true,
      start_time: new Date(),
      docs_read: 0,
      docs_written: 0,
      doc_write_failures: 0,
      errors: []
    };
  
    var changesOpts = {};
    returnValue.ready(src, target);
  
    function initCheckpointer() {
      if (checkpointer) {
        return PouchPromise.resolve();
      }
      return generateReplicationId(src, target, opts).then(function (res) {
        repId = res;
        checkpointer = new Checkpointer(src, target, repId, returnValue);
      });
    }
  
    function writeDocs() {
      changedDocs = [];
  
      if (currentBatch.docs.length === 0) {
        return;
      }
      var docs = currentBatch.docs;
      var bulkOpts = {timeout: opts.timeout};
      return target.bulkDocs({docs: docs, new_edits: false}, bulkOpts).then(function (res) {
        /* istanbul ignore if */
        if (returnValue.cancelled) {
          completeReplication();
          throw new Error('cancelled');
        }
  
        // `res` doesn't include full documents (which live in `docs`), so we create a map of 
        // (id -> error), and check for errors while iterating over `docs`
        var errorsById = Object.create(null);
        res.forEach(function (res) {
          if (res.error) {
            errorsById[res.id] = res;
          }
        });
  
        var errorsNo = Object.keys(errorsById).length;
        result.doc_write_failures += errorsNo;
        result.docs_written += docs.length - errorsNo;
  
        docs.forEach(function (doc) {
          var error = errorsById[doc._id];
          if (error) {
            result.errors.push(error);
            if (error.name === 'unauthorized' || error.name === 'forbidden') {
              returnValue.emit('denied', clone(error));
            } else {
              throw error;
            }
          } else {
            changedDocs.push(doc);
          }
        });
  
      }, function (err) {
        result.doc_write_failures += docs.length;
        throw err;
      });
    }
  
    function finishBatch() {
      if (currentBatch.error) {
        throw new Error('There was a problem getting docs.');
      }
      result.last_seq = last_seq = currentBatch.seq;
      var outResult = clone(result);
      if (changedDocs.length) {
        outResult.docs = changedDocs;
        returnValue.emit('change', outResult);
      }
      writingCheckpoint = true;
      return checkpointer.writeCheckpoint(currentBatch.seq,
          session).then(function () {
        writingCheckpoint = false;
        /* istanbul ignore if */
        if (returnValue.cancelled) {
          completeReplication();
          throw new Error('cancelled');
        }
        currentBatch = undefined;
        getChanges();
      })["catch"](function (err) {
        onCheckpointError(err);
        throw err;
      });
    }
  
    function getDiffs() {
      var diff = {};
      currentBatch.changes.forEach(function (change) {
        // Couchbase Sync Gateway emits these, but we can ignore them
        /* istanbul ignore if */
        if (change.id === "_user/") {
          return;
        }
        diff[change.id] = change.changes.map(function (x) {
          return x.rev;
        });
      });
      return target.revsDiff(diff).then(function (diffs) {
        /* istanbul ignore if */
        if (returnValue.cancelled) {
          completeReplication();
          throw new Error('cancelled');
        }
        // currentBatch.diffs elements are deleted as the documents are written
        currentBatch.diffs = diffs;
      });
    }
  
    function getBatchDocs() {
      return getDocs(src, target, currentBatch.diffs, returnValue).then(function (got) {
        currentBatch.error = !got.ok;
        got.docs.forEach(function (doc) {
          delete currentBatch.diffs[doc._id];
          result.docs_read++;
          currentBatch.docs.push(doc);
        });
      });
    }
  
    function startNextBatch() {
      if (returnValue.cancelled || currentBatch) {
        return;
      }
      if (batches.length === 0) {
        processPendingBatch(true);
        return;
      }
      currentBatch = batches.shift();
      getDiffs()
        .then(getBatchDocs)
        .then(writeDocs)
        .then(finishBatch)
        .then(startNextBatch)[
        "catch"](function (err) {
          abortReplication('batch processing terminated with error', err);
        });
    }
  
  
    function processPendingBatch(immediate) {
      if (pendingBatch.changes.length === 0) {
        if (batches.length === 0 && !currentBatch) {
          if ((continuous && changesOpts.live) || changesCompleted) {
            returnValue.state = 'pending';
            returnValue.emit('paused');
          }
          if (changesCompleted) {
            completeReplication();
          }
        }
        return;
      }
      if (
        immediate ||
        changesCompleted ||
        pendingBatch.changes.length >= batch_size
      ) {
        batches.push(pendingBatch);
        pendingBatch = {
          seq: 0,
          changes: [],
          docs: []
        };
        if (returnValue.state === 'pending' || returnValue.state === 'stopped') {
          returnValue.state = 'active';
          returnValue.emit('active');
        }
        startNextBatch();
      }
    }
  
  
    function abortReplication(reason, err) {
      if (replicationCompleted) {
        return;
      }
      if (!err.message) {
        err.message = reason;
      }
      result.ok = false;
      result.status = 'aborting';
      batches = [];
      pendingBatch = {
        seq: 0,
        changes: [],
        docs: []
      };
      completeReplication(err);
    }
  
  
    function completeReplication(fatalError) {
      if (replicationCompleted) {
        return;
      }
      /* istanbul ignore if */
      if (returnValue.cancelled) {
        result.status = 'cancelled';
        if (writingCheckpoint) {
          return;
        }
      }
      result.status = result.status || 'complete';
      result.end_time = new Date();
      result.last_seq = last_seq;
      replicationCompleted = true;
  
      if (fatalError) {
        fatalError.result = result;
  
        if (fatalError.name === 'unauthorized' || fatalError.name === 'forbidden') {
          returnValue.emit('error', fatalError);
          returnValue.removeAllListeners();
        } else {
          backOff(opts, returnValue, fatalError, function () {
            replicate$1(src, target, opts, returnValue);
          });
        }
      } else {
        returnValue.emit('complete', result);
        returnValue.removeAllListeners();
      }
    }
  
  
    function onChange(change) {
      /* istanbul ignore if */
      if (returnValue.cancelled) {
        return completeReplication();
      }
      var filter = filterChange(opts)(change);
      if (!filter) {
        return;
      }
      pendingBatch.seq = change.seq;
      pendingBatch.changes.push(change);
      processPendingBatch(batches.length === 0 && changesOpts.live);
    }
  
  
    function onChangesComplete(changes) {
      changesPending = false;
      /* istanbul ignore if */
      if (returnValue.cancelled) {
        return completeReplication();
      }
  
      // if no results were returned then we're done,
      // else fetch more
      if (changes.results.length > 0) {
        changesOpts.since = changes.last_seq;
        getChanges();
        processPendingBatch(true);
      } else {
  
        var complete = function () {
          if (continuous) {
            changesOpts.live = true;
            getChanges();
          } else {
            changesCompleted = true;
          }
          processPendingBatch(true);
        };
  
        // update the checkpoint so we start from the right seq next time
        if (!currentBatch && changes.results.length === 0) {
          writingCheckpoint = true;
          checkpointer.writeCheckpoint(changes.last_seq,
              session).then(function () {
            writingCheckpoint = false;
            result.last_seq = last_seq = changes.last_seq;
            complete();
          })[
          "catch"](onCheckpointError);
        } else {
          complete();
        }
      }
    }
  
  
    function onChangesError(err) {
      changesPending = false;
      /* istanbul ignore if */
      if (returnValue.cancelled) {
        return completeReplication();
      }
      abortReplication('changes rejected', err);
    }
  
  
    function getChanges() {
      if (!(
        !changesPending &&
        !changesCompleted &&
        batches.length < batches_limit
        )) {
        return;
      }
      changesPending = true;
      function abortChanges() {
        changes.cancel();
      }
      function removeListener() {
        returnValue.removeListener('cancel', abortChanges);
      }
  
      if (returnValue._changes) { // remove old changes() and listeners
        returnValue.removeListener('cancel', returnValue._abortChanges);
        returnValue._changes.cancel();
      }
      returnValue.once('cancel', abortChanges);
  
      var changes = src.changes(changesOpts)
        .on('change', onChange);
      changes.then(removeListener, removeListener);
      changes.then(onChangesComplete)[
        "catch"](onChangesError);
  
      if (opts.retry) {
        // save for later so we can cancel if necessary
        returnValue._changes = changes;
        returnValue._abortChanges = abortChanges;
      }
    }
  
  
    function startChanges() {
      initCheckpointer().then(function () {
        /* istanbul ignore if */
        if (returnValue.cancelled) {
          completeReplication();
          return;
        }
        return checkpointer.getCheckpoint().then(function (checkpoint) {
          last_seq = checkpoint;
          changesOpts = {
            since: last_seq,
            limit: batch_size,
            batch_size: batch_size,
            style: 'all_docs',
            doc_ids: doc_ids,
            return_docs: true // required so we know when we're done
          };
          if (opts.filter) {
            if (typeof opts.filter !== 'string') {
              // required for the client-side filter in onChange
              changesOpts.include_docs = true;
            } else { // ddoc filter
              changesOpts.filter = opts.filter;
            }
          }
          if ('heartbeat' in opts) {
            changesOpts.heartbeat = opts.heartbeat;
          }
          if ('timeout' in opts) {
            changesOpts.timeout = opts.timeout;
          }
          if (opts.query_params) {
            changesOpts.query_params = opts.query_params;
          }
          if (opts.view) {
            changesOpts.view = opts.view;
          }
          getChanges();
        });
      })["catch"](function (err) {
        abortReplication('getCheckpoint rejected with ', err);
      });
    }
  
    /* istanbul ignore next */
    function onCheckpointError(err) {
      writingCheckpoint = false;
      abortReplication('writeCheckpoint completed with error', err);
    }
  
    /* istanbul ignore if */
    if (returnValue.cancelled) { // cancelled immediately
      completeReplication();
      return;
    }
  
    if (!returnValue._addedListeners) {
      returnValue.once('cancel', completeReplication);
  
      if (typeof opts.complete === 'function') {
        returnValue.once('error', opts.complete);
        returnValue.once('complete', function (result) {
          opts.complete(null, result);
        });
      }
      returnValue._addedListeners = true;
    }
  
    if (typeof opts.since === 'undefined') {
      startChanges();
    } else {
      initCheckpointer().then(function () {
        writingCheckpoint = true;
        return checkpointer.writeCheckpoint(opts.since, session);
      }).then(function () {
        writingCheckpoint = false;
        /* istanbul ignore if */
        if (returnValue.cancelled) {
          completeReplication();
          return;
        }
        last_seq = opts.since;
        startChanges();
      })["catch"](onCheckpointError);
    }
  }
  
  // We create a basic promise so the caller can cancel the replication possibly
  // before we have actually started listening to changes etc
  inherits(Replication, events.EventEmitter);
  function Replication() {
    events.EventEmitter.call(this);
    this.cancelled = false;
    this.state = 'pending';
    var self = this;
    var promise = new PouchPromise(function (fulfill, reject) {
      self.once('complete', fulfill);
      self.once('error', reject);
    });
    self.then = function (resolve, reject) {
      return promise.then(resolve, reject);
    };
    self["catch"] = function (reject) {
      return promise["catch"](reject);
    };
    // As we allow error handling via "error" event as well,
    // put a stub in here so that rejecting never throws UnhandledError.
    self["catch"](function () {});
  }
  
  Replication.prototype.cancel = function () {
    this.cancelled = true;
    this.state = 'cancelled';
    this.emit('cancel');
  };
  
  Replication.prototype.ready = function (src, target) {
    var self = this;
    if (self._readyCalled) {
      return;
    }
    self._readyCalled = true;
  
    function onDestroy() {
      self.cancel();
    }
    src.once('destroyed', onDestroy);
    target.once('destroyed', onDestroy);
    function cleanup() {
      src.removeListener('destroyed', onDestroy);
      target.removeListener('destroyed', onDestroy);
    }
    self.once('complete', cleanup);
  };
  
  function toPouch(db, opts) {
    var PouchConstructor = opts.PouchConstructor;
    if (typeof db === 'string') {
      return new PouchConstructor(db, opts);
    } else {
      return db;
    }
  }
  
  function replicate(src, target, opts, callback) {
  
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
    if (typeof opts === 'undefined') {
      opts = {};
    }
  
    if (opts.doc_ids && !Array.isArray(opts.doc_ids)) {
      throw createError(BAD_REQUEST,
                         "`doc_ids` filter parameter is not a list.");
    }
  
    opts.complete = callback;
    opts = clone(opts);
    opts.continuous = opts.continuous || opts.live;
    opts.retry = ('retry' in opts) ? opts.retry : false;
    /*jshint validthis:true */
    opts.PouchConstructor = opts.PouchConstructor || this;
    var replicateRet = new Replication(opts);
    var srcPouch = toPouch(src, opts);
    var targetPouch = toPouch(target, opts);
    replicate$1(srcPouch, targetPouch, opts, replicateRet);
    return replicateRet;
  }
  
  inherits(Sync, events.EventEmitter);
  function sync(src, target, opts, callback) {
    if (typeof opts === 'function') {
      callback = opts;
      opts = {};
    }
    if (typeof opts === 'undefined') {
      opts = {};
    }
    opts = clone(opts);
    /*jshint validthis:true */
    opts.PouchConstructor = opts.PouchConstructor || this;
    src = toPouch(src, opts);
    target = toPouch(target, opts);
    return new Sync(src, target, opts, callback);
  }
  
  function Sync(src, target, opts, callback) {
    var self = this;
    this.canceled = false;
  
    var optsPush = opts.push ? jsExtend.extend({}, opts, opts.push) : opts;
    var optsPull = opts.pull ? jsExtend.extend({}, opts, opts.pull) : opts;
  
    this.push = replicate(src, target, optsPush);
    this.pull = replicate(target, src, optsPull);
  
    this.pushPaused = true;
    this.pullPaused = true;
  
    function pullChange(change) {
      self.emit('change', {
        direction: 'pull',
        change: change
      });
    }
    function pushChange(change) {
      self.emit('change', {
        direction: 'push',
        change: change
      });
    }
    function pushDenied(doc) {
      self.emit('denied', {
        direction: 'push',
        doc: doc
      });
    }
    function pullDenied(doc) {
      self.emit('denied', {
        direction: 'pull',
        doc: doc
      });
    }
    function pushPaused() {
      self.pushPaused = true;
      /* istanbul ignore if */
      if (self.pullPaused) {
        self.emit('paused');
      }
    }
    function pullPaused() {
      self.pullPaused = true;
      /* istanbul ignore if */
      if (self.pushPaused) {
        self.emit('paused');
      }
    }
    function pushActive() {
      self.pushPaused = false;
      /* istanbul ignore if */
      if (self.pullPaused) {
        self.emit('active', {
          direction: 'push'
        });
      }
    }
    function pullActive() {
      self.pullPaused = false;
      /* istanbul ignore if */
      if (self.pushPaused) {
        self.emit('active', {
          direction: 'pull'
        });
      }
    }
  
    var removed = {};
  
    function removeAll(type) { // type is 'push' or 'pull'
      return function (event, func) {
        var isChange = event === 'change' &&
          (func === pullChange || func === pushChange);
        var isDenied = event === 'denied' &&
          (func === pullDenied || func === pushDenied);
        var isPaused = event === 'paused' &&
          (func === pullPaused || func === pushPaused);
        var isActive = event === 'active' &&
          (func === pullActive || func === pushActive);
  
        if (isChange || isDenied || isPaused || isActive) {
          if (!(event in removed)) {
            removed[event] = {};
          }
          removed[event][type] = true;
          if (Object.keys(removed[event]).length === 2) {
            // both push and pull have asked to be removed
            self.removeAllListeners(event);
          }
        }
      };
    }
  
    if (opts.live) {
      this.push.on('complete', self.pull.cancel.bind(self.pull));
      this.pull.on('complete', self.push.cancel.bind(self.push));
    }
  
    this.on('newListener', function (event) {
      if (event === 'change') {
        self.pull.on('change', pullChange);
        self.push.on('change', pushChange);
      } else if (event === 'denied') {
        self.pull.on('denied', pullDenied);
        self.push.on('denied', pushDenied);
      } else if (event === 'active') {
        self.pull.on('active', pullActive);
        self.push.on('active', pushActive);
      } else if (event === 'paused') {
        self.pull.on('paused', pullPaused);
        self.push.on('paused', pushPaused);
      }
    });
  
    this.on('removeListener', function (event) {
      if (event === 'change') {
        self.pull.removeListener('change', pullChange);
        self.push.removeListener('change', pushChange);
      } else if (event === 'denied') {
        self.pull.removeListener('denied', pullDenied);
        self.push.removeListener('denied', pushDenied);
      } else if (event === 'active') {
        self.pull.removeListener('active', pullActive);
        self.push.removeListener('active', pushActive);
      } else if (event === 'paused') {
        self.pull.removeListener('paused', pullPaused);
        self.push.removeListener('paused', pushPaused);
      }
    });
  
    this.pull.on('removeListener', removeAll('pull'));
    this.push.on('removeListener', removeAll('push'));
  
    var promise = PouchPromise.all([
      this.push,
      this.pull
    ]).then(function (resp) {
      var out = {
        push: resp[0],
        pull: resp[1]
      };
      self.emit('complete', out);
      if (callback) {
        callback(null, out);
      }
      self.removeAllListeners();
      return out;
    }, function (err) {
      self.cancel();
      if (callback) {
        // if there's a callback, then the callback can receive
        // the error event
        callback(err);
      } else {
        // if there's no callback, then we're safe to emit an error
        // event, which would otherwise throw an unhandled error
        // due to 'error' being a special event in EventEmitters
        self.emit('error', err);
      }
      self.removeAllListeners();
      if (callback) {
        // no sense throwing if we're already emitting an 'error' event
        throw err;
      }
    });
  
    this.then = function (success, err) {
      return promise.then(success, err);
    };
  
    this["catch"] = function (err) {
      return promise["catch"](err);
    };
  }
  
  Sync.prototype.cancel = function () {
    if (!this.canceled) {
      this.canceled = true;
      this.push.cancel();
      this.pull.cancel();
    }
  };
  
  function replication(PouchDB) {
    PouchDB.replicate = replicate;
    PouchDB.sync = sync;
  
    Object.defineProperty(PouchDB.prototype, 'replicate', {
      get: function () {
        var self = this;
        return {
          from: function (other, opts, callback) {
            return self.constructor.replicate(other, self, opts, callback);
          },
          to: function (other, opts, callback) {
            return self.constructor.replicate(self, other, opts, callback);
          }
        };
      }
    });
  
    PouchDB.prototype.sync = function (dbName, opts, callback) {
      return this.constructor.sync(this, dbName, opts, callback);
    };
  }
  
  PouchDB.plugin(IDBPouch)
    .plugin(WebSqlPouch)
    .plugin(HttpPouch$1)
    .plugin(mapreduce)
    .plugin(replication);
  
  // Pull from src because pouchdb-node/pouchdb-browser themselves
  // are aggressively optimized and jsnext:main would normally give us this
  // aggressive bundle.
  
  module.exports = PouchDB;
  }).call(this,_dereq_(11),typeof global !== "undefined" ? global : typeof self !== "undefined" ? self : typeof window !== "undefined" ? window : {})
  },{"1":1,"11":11,"12":12,"13":13,"14":14,"2":2,"4":4,"5":5,"7":7,"8":8,"9":9}]},{},[15])(15)
  });