text: "use strict";
  
  var EventEmitter = require('events').EventEmitter
    , inherits = require('util').inherits
    , getSingleProperty = require('./utils').getSingleProperty
    , shallowClone = require('./utils').shallowClone
    , parseIndexOptions = require('./utils').parseIndexOptions
    , debugOptions = require('./utils').debugOptions
    , CommandCursor = require('./command_cursor')
    , handleCallback = require('./utils').handleCallback
    , toError = require('./utils').toError
    , ReadPreference = require('./read_preference')
    , f = require('util').format
    , Admin = require('./admin')
    , Code = require('mongodb-core').BSON.Code
    , CoreReadPreference = require('mongodb-core').ReadPreference
    , MongoError = require('mongodb-core').MongoError
    , ObjectID = require('mongodb-core').ObjectID
    , Define = require('./metadata')
    , Logger = require('mongodb-core').Logger
    , Collection = require('./collection')
    , crypto = require('crypto');
  
  var debugFields = ['authSource', 'w', 'wtimeout', 'j', 'native_parser', 'forceServerObjectId'
    , 'serializeFunctions', 'raw', 'promoteLongs', 'bufferMaxEntries', 'numberOfRetries', 'retryMiliSeconds'
    , 'readPreference', 'pkFactory'];
  
  /**
   * @fileOverview The **Db** class is a class that represents a MongoDB Database.
   *
   * @example
   * var MongoClient = require('mongodb').MongoClient,
   *   test = require('assert');
   * // Connection url
   * var url = 'mongodb://localhost:27017/test';
   * // Connect using MongoClient
   * MongoClient.connect(url, function(err, db) {
   *   // Get an additional db
   *   var testDb = db.db('test');
   *   db.close();
   * });
   */
  
  /**
   * Creates a new Db instance
   * @class
   * @param {string} databaseName The name of the database this instance represents.
   * @param {(Server|ReplSet|Mongos)} topology The server topology for the database.
   * @param {object} [options=null] Optional settings.
   * @param {string} [options.authSource=null] If the database authentication is dependent on another databaseName.
   * @param {(number|string)} [options.w=null] The write concern.
   * @param {number} [options.wtimeout=null] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.native_parser=true] Select C++ bson parser instead of JavaScript parser.
   * @param {boolean} [options.forceServerObjectId=false] Force server to assign _id values instead of driver.
   * @param {boolean} [options.serializeFunctions=false] Serialize functions on any object.
   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
   * @param {boolean} [options.raw=false] Return document results as raw BSON buffers.
   * @param {boolean} [options.promoteLongs=true] Promotes Long values to number if they fit inside the 53 bits resolution.
   * @param {number} [options.bufferMaxEntries=-1] Sets a cap on how many operations the driver will buffer up before giving up on getting a working connection, default is -1 which is unlimited.
   * @param {(ReadPreference|string)} [options.readPreference=null] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {object} [options.pkFactory=null] A primary key factory object for generation of custom _id keys.
   * @param {object} [options.promiseLibrary=null] A Promise library class the application wishes to use such as Bluebird, must be ES6 compatible
   * @param {object} [options.readConcern=null] Specify a read concern for the collection. (only MongoDB 3.2 or higher supported)
   * @param {object} [options.readConcern.level='local'] Specify a read concern level for the collection operations, one of [local|majority]. (only MongoDB 3.2 or higher supported)
   * @property {(Server|ReplSet|Mongos)} serverConfig Get the current db topology.
   * @property {number} bufferMaxEntries Current bufferMaxEntries value for the database
   * @property {string} databaseName The name of the database this instance represents.
   * @property {object} options The options associated with the db instance.
   * @property {boolean} native_parser The current value of the parameter native_parser.
   * @property {boolean} slaveOk The current slaveOk value for the db instance.
   * @property {object} writeConcern The current write concern values.
   * @fires Db#close
   * @fires Db#authenticated
   * @fires Db#reconnect
   * @fires Db#error
   * @fires Db#timeout
   * @fires Db#parseError
   * @fires Db#fullsetup
   * @return {Db} a Db instance.
   */
  var Db = function(databaseName, topology, options) {
    options = options || {};
    if(!(this instanceof Db)) return new Db(databaseName, topology, options);
    EventEmitter.call(this);
    var self = this;
  
    // Get the promiseLibrary
    var promiseLibrary = options.promiseLibrary;
  
    // No promise library selected fall back
    if(!promiseLibrary) {
      promiseLibrary = typeof global.Promise == 'function' ?
        global.Promise : require('es6-promise').Promise;
    }
  
    // Ensure we put the promiseLib in the options
    options.promiseLibrary = promiseLibrary;
  
    // var self = this;  // Internal state of the db object
    this.s = {
      // Database name
        databaseName: databaseName
      // DbCache
      , dbCache: {}
      // Children db's
      , children: []
      // Topology
      , topology: topology
      // Options
      , options: options
      // Logger instance
      , logger: Logger('Db', options)
      // Get the bson parser
      , bson: topology ? topology.bson : null
      // Authsource if any
      , authSource: options.authSource
      // Unpack read preference
      , readPreference: options.readPreference
      // Set buffermaxEntries
      , bufferMaxEntries: typeof options.bufferMaxEntries == 'number' ? options.bufferMaxEntries : -1
      // Parent db (if chained)
      , parentDb: options.parentDb || null
      // Set up the primary key factory or fallback to ObjectID
      , pkFactory: options.pkFactory || ObjectID
      // Get native parser
      , nativeParser: options.nativeParser || options.native_parser
      // Promise library
      , promiseLibrary: promiseLibrary
      // No listener
      , noListener: typeof options.noListener == 'boolean' ? options.noListener : false
      // ReadConcern
      , readConcern: options.readConcern
    }
  
    // Ensure we have a valid db name
    validateDatabaseName(self.s.databaseName);
  
    // If we have specified the type of parser
    if(typeof self.s.nativeParser == 'boolean') {
      if(self.s.nativeParser) {
        topology.setBSONParserType("c++");
      } else {
        topology.setBSONParserType("js");
      }
    }
  
    // Add a read Only property
    getSingleProperty(this, 'serverConfig', self.s.topology);
    getSingleProperty(this, 'bufferMaxEntries', self.s.bufferMaxEntries);
    getSingleProperty(this, 'databaseName', self.s.databaseName);
  
    // Last ismaster
    Object.defineProperty(this, 'options', {
      enumerable:true,
      get: function() { return self.s.options; }
    });
  
    // Last ismaster
    Object.defineProperty(this, 'native_parser', {
      enumerable:true,
      get: function() { return self.s.topology.parserType() == 'c++'; }
    });
  
    // Last ismaster
    Object.defineProperty(this, 'slaveOk', {
      enumerable:true,
      get: function() {
        if(self.s.options.readPreference != null
          && (self.s.options.readPreference != 'primary' || self.s.options.readPreference.mode != 'primary')) {
          return true;
        }
        return false;
      }
    });
  
    Object.defineProperty(this, 'writeConcern', {
      enumerable:true,
      get: function() {
        var ops = {};
        if(self.s.options.w != null) ops.w = self.s.options.w;
        if(self.s.options.j != null) ops.j = self.s.options.j;
        if(self.s.options.fsync != null) ops.fsync = self.s.options.fsync;
        if(self.s.options.wtimeout != null) ops.wtimeout = self.s.options.wtimeout;
        return ops;
      }
    });
  
    // This is a child db, do not register any listeners
    if(options.parentDb) return;
    if(this.s.noListener) return;
  
    // Add listeners
    topology.on('error', createListener(self, 'error', self));
    topology.on('timeout', createListener(self, 'timeout', self));
    topology.on('close', createListener(self, 'close', self));
    topology.on('parseError', createListener(self, 'parseError', self));
    topology.once('open', createListener(self, 'open', self));
    topology.once('fullsetup', createListener(self, 'fullsetup', self));
    topology.once('all', createListener(self, 'all', self));
    topology.on('reconnect', createListener(self, 'reconnect', self));
  }
  
  inherits(Db, EventEmitter);
  
  var define = Db.define = new Define('Db', Db, false);
  
  /**
   * The callback format for the Db.open method
   * @callback Db~openCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Db} db The Db instance if the open method was successful.
   */
  
  // Internal method
  var open = function(self, callback) {
    self.s.topology.connect(self, self.s.options, function(err, topology) {
      if(callback == null) return;
      var internalCallback = callback;
      callback == null;
  
      if(err) {
        self.close();
        return internalCallback(err);
      }
  
      internalCallback(null, self);
    });
  }
  
  /**
   * Open the database
   * @method
   * @param {Db~openCallback} [callback] Callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.open = function(callback) {
    var self = this;
    // We provided a callback leg
    if(typeof callback == 'function') return open(self, callback);
    // Return promise
    return new self.s.promiseLibrary(function(resolve, reject) {
      open(self, function(err, db) {
        if(err) return reject(err);
        resolve(db);
      })
    });
  }
  
  define.classMethod('open', {callback: true, promise:true});
  
  /**
   * The callback format for results
   * @callback Db~resultCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {object} result The result object if the command was executed successfully.
   */
  
  var executeCommand = function(self, command, options, callback) {
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
    // Get the db name we are executing against
    var dbName = options.dbName || options.authdb || self.s.databaseName;
    // If we have a readPreference set
    if(options.readPreference == null && self.s.readPreference) {
      options.readPreference = self.s.readPreference;
    }
  
    // Convert the readPreference
    if(options.readPreference && typeof options.readPreference == 'string') {
      options.readPreference = new CoreReadPreference(options.readPreference);
    } else if(options.readPreference instanceof ReadPreference) {
      options.readPreference = new CoreReadPreference(options.readPreference.mode
        , options.readPreference.tags);
    }
  
    // Debug information
    if(self.s.logger.isDebug()) self.s.logger.debug(f('executing command %s against %s with options [%s]'
      , JSON.stringify(command), f('%s.$cmd', dbName), JSON.stringify(debugOptions(debugFields, options))));
  
    // Execute command
    self.s.topology.command(f('%s.$cmd', dbName), command, options, function(err, result) {
      if(err) return handleCallback(callback, err);
      if(options.full) return handleCallback(callback, null, result);
      handleCallback(callback, null, result.result);
    });
  }
  
  /**
   * Execute a command
   * @method
   * @param {object} command The command hash
   * @param {object} [options=null] Optional settings.
   * @param {(ReadPreference|string)} [options.readPreference=null] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.command = function(command, options, callback) {
    var self = this;
    // Change the callback
    if(typeof options == 'function') callback = options, options = {};
    // Clone the options
    options = shallowClone(options);
  
    // Do we have a callback
    if(typeof callback == 'function') return executeCommand(self, command, options, callback);
    // Return a promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      executeCommand(self, command, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  }
  
  define.classMethod('command', {callback: true, promise:true});
  
  /**
   * The callback format for results
   * @callback Db~noResultCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {null} result Is not set to a value
   */
  
  /**
   * Close the db and it's underlying connections
   * @method
   * @param {boolean} force Force close, emitting no events
   * @param {Db~noResultCallback} [callback] The result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.close = function(force, callback) {
    if(typeof force == 'function') callback = force, force = false;
    this.s.topology.close(force);
    var self = this;
  
    // Fire close event if any listeners
    if(this.listeners('close').length > 0) {
      this.emit('close');
  
      // If it's the top level db emit close on all children
      if(this.parentDb == null) {
        // Fire close on all children
        for(var i = 0; i < this.s.children.length; i++) {
          this.s.children[i].emit('close');
        }
      }
  
      // Remove listeners after emit
      self.removeAllListeners('close');
    }
  
    // Close parent db if set
    if(this.s.parentDb) this.s.parentDb.close();
    // Callback after next event loop tick
    if(typeof callback == 'function') return process.nextTick(function() {
      handleCallback(callback, null);
    })
  
    // Return dummy promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      resolve();
    });
  }
  
  define.classMethod('close', {callback: true, promise:true});
  
  /**
   * Return the Admin db instance
   * @method
   * @return {Admin} return the new Admin db instance
   */
  Db.prototype.admin = function() {
    return new Admin(this, this.s.topology, this.s.promiseLibrary);
  };
  
  define.classMethod('admin', {callback: false, promise:false, returns: [Admin]});
  
  /**
   * The callback format for the collection method, must be used if strict is specified
   * @callback Db~collectionResultCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection} collection The collection instance.
   */
  
  /**
   * Fetch a specific collection (containing the actual collection information). If the application does not use strict mode you can
   * can use it without a callback in the following way. var collection = db.collection('mycollection');
   *
   * @method
   * @param {string} name the collection name we wish to access.
   * @param {object} [options=null] Optional settings.
   * @param {(number|string)} [options.w=null] The write concern.
   * @param {number} [options.wtimeout=null] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.raw=false] Return document results as raw BSON buffers.
   * @param {object} [options.pkFactory=null] A primary key factory object for generation of custom _id keys.
   * @param {(ReadPreference|string)} [options.readPreference=null] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {boolean} [options.serializeFunctions=false] Serialize functions on any object.
   * @param {boolean} [options.strict=false] Returns an error if the collection does not exist
   * @param {object} [options.readConcern=null] Specify a read concern for the collection. (only MongoDB 3.2 or higher supported)
   * @param {object} [options.readConcern.level='local'] Specify a read concern level for the collection operations, one of [local|majority]. (only MongoDB 3.2 or higher supported)
   * @param {Db~collectionResultCallback} callback The collection result callback
   * @return {Collection} return the new Collection instance if not in strict mode
   */
  Db.prototype.collection = function(name, options, callback) {
    var self = this;
    if(typeof options == 'function') callback = options, options = {};
    options = options || {};
    options = shallowClone(options);
    // Set the promise library
    options.promiseLibrary = this.s.promiseLibrary;
  
    // If we have not set a collection level readConcern set the db level one
    options.readConcern = options.readConcern || this.s.readConcern;
  
    // Do we have ignoreUndefined set
    if(this.s.options.ignoreUndefined) {
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    // Execute
    if(options == null || !options.strict) {
      try {
        var collection = new Collection(this, this.s.topology, this.s.databaseName, name, this.s.pkFactory, options);
        if(callback) callback(null, collection);
        return collection;
      } catch(err) {
        if(callback) return callback(err);
        throw err;
      }
    }
  
    // Strict mode
    if(typeof callback != 'function') {
      throw toError(f("A callback is required in strict mode. While getting collection %s.", name));
    }
  
    // Strict mode
    this.listCollections({name:name}).toArray(function(err, collections) {
      if(err != null) return handleCallback(callback, err, null);
      if(collections.length == 0) return handleCallback(callback, toError(f("Collection %s does not exist. Currently in strict mode.", name)), null);
  
      try {
        return handleCallback(callback, null, new Collection(self, self.s.topology, self.s.databaseName, name, self.s.pkFactory, options));
      } catch(err) {
        return handleCallback(callback, err, null);
      }
    });
  }
  
  define.classMethod('collection', {callback: true, promise:false, returns: [Collection]});
  
  var createCollection = function(self, name, options, callback) {
    // Get the write concern options
    var finalOptions = writeConcern(shallowClone(options), self, options);
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
  
    // Check if we have the name
    self.listCollections({name: name}).toArray(function(err, collections) {
      if(err != null) return handleCallback(callback, err, null);
      if(collections.length > 0 && finalOptions.strict) {
        return handleCallback(callback, MongoError.create({message: f("Collection %s already exists. Currently in strict mode.", name), driver:true}), null);
      } else if (collections.length > 0) {
        try { return handleCallback(callback, null, new Collection(self, self.s.topology, self.s.databaseName, name, self.s.pkFactory, options)); }
        catch(err) { return handleCallback(callback, err); }
      }
  
      // Create collection command
      var cmd = {'create':name};
  
      // Add all optional parameters
      for(var n in options) {
        if(options[n] != null && typeof options[n] != 'function')
          cmd[n] = options[n];
      }
  
      // Execute command
      self.command(cmd, finalOptions, function(err, result) {
        if(err) return handleCallback(callback, err);
        handleCallback(callback, null, new Collection(self, self.s.topology, self.s.databaseName, name, self.s.pkFactory, options));
      });
    });
  }
  
  /**
   * Creates a collection on a server pre-allocating space, need to create f.ex capped collections.
   *
   * @method
   * @param {string} name the collection name we wish to access.
   * @param {object} [options=null] Optional settings.
   * @param {(number|string)} [options.w=null] The write concern.
   * @param {number} [options.wtimeout=null] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.raw=false] Return document results as raw BSON buffers.
   * @param {object} [options.pkFactory=null] A primary key factory object for generation of custom _id keys.
   * @param {(ReadPreference|string)} [options.readPreference=null] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {boolean} [options.serializeFunctions=false] Serialize functions on any object.
   * @param {boolean} [options.strict=false] Returns an error if the collection does not exist
   * @param {boolean} [options.capped=false] Create a capped collection.
   * @param {number} [options.size=null] The size of the capped collection in bytes.
   * @param {number} [options.max=null] The maximum number of documents in the capped collection.
   * @param {boolean} [options.autoIndexId=true] Create an index on the _id field of the document, True by default on MongoDB 2.2 or higher off for version < 2.2.
   * @param {Db~collectionResultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.createCollection = function(name, options, callback) {
    var self = this;
    var args = Array.prototype.slice.call(arguments, 0);
    callback = args.pop();
    if(typeof callback != 'function') args.push(callback);
    name = args.length ? args.shift() : null;
    options = args.length ? args.shift() || {} : {};
  
    // Do we have a promisesLibrary
    options.promiseLibrary = options.promiseLibrary || this.s.promiseLibrary;
  
    // Check if the callback is in fact a string
    if(typeof callback == 'string') name = callback;
  
    // Execute the fallback callback
    if(typeof callback == 'function') return createCollection(self, name, options, callback);
    return new this.s.promiseLibrary(function(resolve, reject) {
      createCollection(self, name, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  }
  
  define.classMethod('createCollection', {callback: true, promise:true});
  
  /**
   * Get all the db statistics.
   *
   * @method
   * @param {object} [options=null] Optional settings.
   * @param {number} [options.scale=null] Divide the returned sizes by scale value.
   * @param {Db~resultCallback} [callback] The collection result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.stats = function(options, callback) {
    if(typeof options == 'function') callback = options, options = {};
    options = options || {};
    // Build command object
    var commandObject = { dbStats:true };
    // Check if we have the scale value
    if(options['scale'] != null) commandObject['scale'] = options['scale'];
    // Execute the command
    return this.command(commandObject, options, callback);
  }
  
  define.classMethod('stats', {callback: true, promise:true});
  
  // Transformation methods for cursor results
  var listCollectionsTranforms = function(databaseName) {
    var matching = f('%s.', databaseName);
  
    return {
      doc: function(doc) {
        var index = doc.name.indexOf(matching);
        // Remove database name if available
        if(doc.name && index == 0) {
          doc.name = doc.name.substr(index + matching.length);
        }
  
        return doc;
      }
    }
  }
  
  /**
   * Get the list of all collection information for the specified db.
   *
   * @method
   * @param {object} filter Query to filter collections by
   * @param {object} [options=null] Optional settings.
   * @param {number} [options.batchSize=null] The batchSize for the returned command cursor or if pre 2.8 the systems batch collection
   * @param {(ReadPreference|string)} [options.readPreference=null] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @return {CommandCursor}
   */
  Db.prototype.listCollections = function(filter, options) {
    filter = filter || {};
    options = options || {};
  
    // Shallow clone the object
    options = shallowClone(options);
    // Set the promise library
    options.promiseLibrary = this.s.promiseLibrary;
    // We have a list collections command
    if(this.serverConfig.capabilities().hasListCollectionsCommand) {
      // Cursor options
      var cursor = options.batchSize ? {batchSize: options.batchSize} : {}
      // Build the command
      var command = { listCollections : true, filter: filter, cursor: cursor };
      // Set the AggregationCursor constructor
      options.cursorFactory = CommandCursor;
      // Filter out the correct field values
      options.transforms = listCollectionsTranforms(this.s.databaseName);
      // Create the cursor
      var cursor = this.s.topology.cursor(f('%s.$cmd', this.s.databaseName), command, options);
      // Do we have a readPreference, apply it
      if(options.readPeference) cursor.setReadPreference(options.readPeference);
      // Return the cursor
      return cursor;
    }
  
    // We cannot use the listCollectionsCommand
    if(!this.serverConfig.capabilities().hasListCollectionsCommand) {
      // If we have legacy mode and have not provided a full db name filter it
      if(typeof filter.name == 'string' && !(new RegExp('^' + this.databaseName + '\\.').test(filter.name))) {
        filter = shallowClone(filter);
        filter.name = f('%s.%s', this.s.databaseName, filter.name);
      }
    }
  
    // No filter, filter by current database
    if(filter == null) {
      filter.name = f('/%s/', this.s.databaseName);
    }
  
    // Rewrite the filter to use $and to filter out indexes
    if(filter.name) {
      filter = {$and: [{name: filter.name}, {name:/^((?!\$).)*$/}]};
    } else {
      filter = {name:/^((?!\$).)*$/};
    }
  
    // Return options
    var _options = {transforms: listCollectionsTranforms(this.s.databaseName)}
    // Get the cursor
    var cursor = this.collection(Db.SYSTEM_NAMESPACE_COLLECTION).find(filter, _options);
    // Do we have a readPreference, apply it
    if(options.readPeference) cursor.setReadPreference(options.readPeference);
    // Set the passed in batch size if one was provided
    if(options.batchSize) cursor = cursor.batchSize(options.batchSize);
    // We have a fallback mode using legacy systems collections
    return cursor;
  };
  
  define.classMethod('listCollections', {callback: false, promise:false, returns: [CommandCursor]});
  
  var evaluate = function(self, code, parameters, options, callback) {
    var finalCode = code;
    var finalParameters = [];
  
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
  
    // If not a code object translate to one
    if(!(finalCode instanceof Code)) finalCode = new Code(finalCode);
    // Ensure the parameters are correct
    if(parameters != null && !Array.isArray(parameters) && typeof parameters !== 'function') {
      finalParameters = [parameters];
    } else if(parameters != null && Array.isArray(parameters) && typeof parameters !== 'function') {
      finalParameters = parameters;
    }
  
    // Create execution selector
    var cmd = {'$eval':finalCode, 'args':finalParameters};
    // Check if the nolock parameter is passed in
    if(options['nolock']) {
      cmd['nolock'] = options['nolock'];
    }
  
    // Set primary read preference
    options.readPreference = new CoreReadPreference(ReadPreference.PRIMARY);
  
    // Execute the command
    self.command(cmd, options, function(err, result) {
      if(err) return handleCallback(callback, err, null);
      if(result && result.ok == 1) return handleCallback(callback, null, result.retval);
      if(result) return handleCallback(callback, MongoError.create({message: f("eval failed: %s", result.errmsg), driver:true}), null);
      handleCallback(callback, err, result);
    });
  }
  
  /**
   * Evaluate JavaScript on the server
   *
   * @method
   * @param {Code} code JavaScript to execute on server.
   * @param {(object|array)} parameters The parameters for the call.
   * @param {object} [options=null] Optional settings.
   * @param {boolean} [options.nolock=false] Tell MongoDB not to block on the evaulation of the javascript.
   * @param {Db~resultCallback} [callback] The results callback
   * @deprecated Eval is deprecated on MongoDB 3.2 and forward
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.eval = function(code, parameters, options, callback) {
    var self = this;
    var args = Array.prototype.slice.call(arguments, 1);
    callback = args.pop();
    if(typeof callback != 'function') args.push(callback);
    parameters = args.length ? args.shift() : parameters;
    options = args.length ? args.shift() || {} : {};
  
    // Check if the callback is in fact a string
    if(typeof callback == 'function') return evaluate(self, code, parameters, options, callback);
    // Execute the command
    return new this.s.promiseLibrary(function(resolve, reject) {
      evaluate(self, code, parameters, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  define.classMethod('eval', {callback: true, promise:true});
  
  /**
   * Rename a collection.
   *
   * @method
   * @param {string} fromCollection Name of current collection to rename.
   * @param {string} toCollection New name of of the collection.
   * @param {object} [options=null] Optional settings.
   * @param {boolean} [options.dropTarget=false] Drop the target name collection if it previously exists.
   * @param {Db~collectionResultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.renameCollection = function(fromCollection, toCollection, options, callback) {
    var self = this;
    if(typeof options == 'function') callback = options, options = {};
    options = options || {};
    // Add return new collection
    options.new_collection = true;
  
    // Check if the callback is in fact a string
    if(typeof callback == 'function') {
      return this.collection(fromCollection).rename(toCollection, options, callback);
    }
  
    // Return a promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      self.collection(fromCollection).rename(toCollection, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  define.classMethod('renameCollection', {callback: true, promise:true});
  
  /**
   * Drop a collection from the database, removing it permanently. New accesses will create a new collection.
   *
   * @method
   * @param {string} name Name of collection to drop
   * @param {Db~resultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.dropCollection = function(name, callback) {
    var self = this;
  
    // Command to execute
    var cmd = {'drop':name}
  
    // Check if the callback is in fact a string
    if(typeof callback == 'function') return this.command(cmd, this.s.options, function(err, result) {
      // Did the user destroy the topology
      if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
      if(err) return handleCallback(callback, err);
      if(result.ok) return handleCallback(callback, null, true);
      handleCallback(callback, null, false);
    });
  
    // Execute the command
    return new this.s.promiseLibrary(function(resolve, reject) {
      // Execute command
      self.command(cmd, self.s.options, function(err, result) {
        // Did the user destroy the topology
        if(self.serverConfig && self.serverConfig.isDestroyed()) return reject(new MongoError('topology was destroyed'));
        if(err) return reject(err);
        if(result.ok) return resolve(true);
        resolve(false);
      });
    });
  };
  
  define.classMethod('dropCollection', {callback: true, promise:true});
  
  /**
   * Drop a database.
   *
   * @method
   * @param {Db~resultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.dropDatabase = function(callback) {
    var self = this;
    // Drop database command
    var cmd = {'dropDatabase':1};
  
    // Check if the callback is in fact a string
    if(typeof callback == 'function') return this.command(cmd, this.s.options, function(err, result) {
      // Did the user destroy the topology
      if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
      if(callback == null) return;
      if(err) return handleCallback(callback, err, null);
      handleCallback(callback, null, result.ok ? true : false);
    });
  
    // Execute the command
    return new this.s.promiseLibrary(function(resolve, reject) {
      // Execute command
      self.command(cmd, self.s.options, function(err, result) {
        // Did the user destroy the topology
        if(self.serverConfig && self.serverConfig.isDestroyed()) return reject(new MongoError('topology was destroyed'));
        if(err) return reject(err);
        if(result.ok) return resolve(true);
        resolve(false);
      });
    });
  }
  
  define.classMethod('dropDatabase', {callback: true, promise:true});
  
  /**
   * The callback format for the collections method.
   * @callback Db~collectionsResultCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection[]} collections An array of all the collections objects for the db instance.
   */
  var collections = function(self, callback) {
    // Let's get the collection names
    self.listCollections().toArray(function(err, documents) {
      if(err != null) return handleCallback(callback, err, null);
      // Filter collections removing any illegal ones
      documents = documents.filter(function(doc) {
        return doc.name.indexOf('$') == -1;
      });
  
      // Return the collection objects
      handleCallback(callback, null, documents.map(function(d) {
        return new Collection(self, self.s.topology, self.s.databaseName, d.name.replace(self.s.databaseName + ".", ''), self.s.pkFactory, self.s.options);
      }));
    });
  }
  
  /**
   * Fetch all collections for the current db.
   *
   * @method
   * @param {Db~collectionsResultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.collections = function(callback) {
    var self = this;
  
    // Return the callback
    if(typeof callback == 'function') return collections(self, callback);
    // Return the promise
    return new self.s.promiseLibrary(function(resolve, reject) {
      collections(self, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  define.classMethod('collections', {callback: true, promise:true});
  
  /**
   * Runs a command on the database as admin.
   * @method
   * @param {object} command The command hash
   * @param {object} [options=null] Optional settings.
   * @param {(ReadPreference|string)} [options.readPreference=null] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {number} [options.maxTimeMS=null] Number of milliseconds to wait before aborting the query.
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.executeDbAdminCommand = function(selector, options, callback) {
    var self = this;
    if(typeof options == 'function') callback = options, options = {};
    options = options || {};
  
    if(options.readPreference) {
      options.readPreference = options.readPreference;
    }
  
    // Return the callback
    if(typeof callback == 'function') return self.s.topology.command('admin.$cmd', selector, options, function(err, result) {
      // Did the user destroy the topology
      if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
      if(err) return handleCallback(callback, err);
      handleCallback(callback, null, result.result);
    });
  
    // Return promise
    return new self.s.promiseLibrary(function(resolve, reject) {
      self.s.topology.command('admin.$cmd', selector, options, function(err, result) {
        // Did the user destroy the topology
        if(self.serverConfig && self.serverConfig.isDestroyed()) return reject(new MongoError('topology was destroyed'));
        if(err) return reject(err);
        resolve(result.result);
      });
    });
  };
  
  define.classMethod('executeDbAdminCommand', {callback: true, promise:true});
  
  /**
   * Creates an index on the db and collection collection.
   * @method
   * @param {string} name Name of the collection to create the index on.
   * @param {(string|object)} fieldOrSpec Defines the index.
   * @param {object} [options=null] Optional settings.
   * @param {(number|string)} [options.w=null] The write concern.
   * @param {number} [options.wtimeout=null] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.unique=false] Creates an unique index.
   * @param {boolean} [options.sparse=false] Creates a sparse index.
   * @param {boolean} [options.background=false] Creates the index in the background, yielding whenever possible.
   * @param {boolean} [options.dropDups=false] A unique index cannot be created on a key that has pre-existing duplicate values. If you would like to create the index anyway, keeping the first document the database indexes and deleting all subsequent documents that have duplicate value
   * @param {number} [options.min=null] For geospatial indexes set the lower bound for the co-ordinates.
   * @param {number} [options.max=null] For geospatial indexes set the high bound for the co-ordinates.
   * @param {number} [options.v=null] Specify the format version of the indexes.
   * @param {number} [options.expireAfterSeconds=null] Allows you to expire data on indexes applied to a data (MongoDB 2.2 or higher)
   * @param {number} [options.name=null] Override the autogenerated index name (useful if the resulting name is larger than 128 bytes)
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.createIndex = function(name, fieldOrSpec, options, callback) {
    var self = this;
    var args = Array.prototype.slice.call(arguments, 2);
    callback = args.pop();
    if(typeof callback != 'function') args.push(callback);
    options = args.length ? args.shift() || {} : {};
    options = typeof callback === 'function' ? options : callback;
    options = options == null ? {} : options;
    // Shallow clone the options
    options = shallowClone(options);
    // Run only against primary
    options.readPreference = ReadPreference.PRIMARY;
  
    // If we have a callback fallback
    if(typeof callback == 'function') return createIndex(self, name, fieldOrSpec, options, callback);
    // Return a promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      createIndex(self, name, fieldOrSpec, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  var createIndex = function(self, name, fieldOrSpec, options, callback) {
    // Get the write concern options
    var finalOptions = writeConcern({}, self, options);
    // Ensure we have a callback
    if(finalOptions.writeConcern && typeof callback != 'function') {
      throw MongoError.create({message: "Cannot use a writeConcern without a provided callback", driver:true});
    }
  
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
  
    // Attempt to run using createIndexes command
    createIndexUsingCreateIndexes(self, name, fieldOrSpec, options, function(err, result) {
      if(err == null) return handleCallback(callback, err, result);
      // Create command
      var doc = createCreateIndexCommand(self, name, fieldOrSpec, options);
      // Set no key checking
      finalOptions.checkKeys = false;
      // Insert document
      self.s.topology.insert(f("%s.%s", self.s.databaseName, Db.SYSTEM_INDEX_COLLECTION), doc, finalOptions, function(err, result) {
        if(callback == null) return;
        if(err) return handleCallback(callback, err);
        if(result == null) return handleCallback(callback, null, null);
        if(result.result.writeErrors) return handleCallback(callback, MongoError.create(result.result.writeErrors[0]), null);
        handleCallback(callback, null, doc.name);
      });
    });
  }
  
  define.classMethod('createIndex', {callback: true, promise:true});
  
  /**
   * Ensures that an index exists, if it does not it creates it
   * @method
   * @deprecated since version 2.0
   * @param {string} name The index name
   * @param {(string|object)} fieldOrSpec Defines the index.
   * @param {object} [options=null] Optional settings.
   * @param {(number|string)} [options.w=null] The write concern.
   * @param {number} [options.wtimeout=null] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.unique=false] Creates an unique index.
   * @param {boolean} [options.sparse=false] Creates a sparse index.
   * @param {boolean} [options.background=false] Creates the index in the background, yielding whenever possible.
   * @param {boolean} [options.dropDups=false] A unique index cannot be created on a key that has pre-existing duplicate values. If you would like to create the index anyway, keeping the first document the database indexes and deleting all subsequent documents that have duplicate value
   * @param {number} [options.min=null] For geospatial indexes set the lower bound for the co-ordinates.
   * @param {number} [options.max=null] For geospatial indexes set the high bound for the co-ordinates.
   * @param {number} [options.v=null] Specify the format version of the indexes.
   * @param {number} [options.expireAfterSeconds=null] Allows you to expire data on indexes applied to a data (MongoDB 2.2 or higher)
   * @param {number} [options.name=null] Override the autogenerated index name (useful if the resulting name is larger than 128 bytes)
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.ensureIndex = function(name, fieldOrSpec, options, callback) {
    var self = this;
    if(typeof options == 'function') callback = options, options = {};
    options = options || {};
  
    // If we have a callback fallback
    if(typeof callback == 'function') return ensureIndex(self, name, fieldOrSpec, options, callback);
  
    // Return a promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      ensureIndex(self, name, fieldOrSpec, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  var ensureIndex = function(self, name, fieldOrSpec, options, callback) {
    // Get the write concern options
    var finalOptions = writeConcern({}, self, options);
    // Create command
    var selector = createCreateIndexCommand(self, name, fieldOrSpec, options);
    var index_name = selector.name;
  
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
  
    // Default command options
    var commandOptions = {};
    // Check if the index allready exists
    self.indexInformation(name, finalOptions, function(err, indexInformation) {
      if(err != null && err.code != 26) return handleCallback(callback, err, null);
      // If the index does not exist, create it
      if(indexInformation == null || !indexInformation[index_name])  {
        self.createIndex(name, fieldOrSpec, options, callback);
      } else {
        if(typeof callback === 'function') return handleCallback(callback, null, index_name);
      }
    });
  }
  
  define.classMethod('ensureIndex', {callback: true, promise:true});
  
  Db.prototype.addChild = function(db) {
    if(this.s.parentDb) return this.s.parentDb.addChild(db);
    this.s.children.push(db);
  }
  
  /**
   * Create a new Db instance sharing the current socket connections. Be aware that the new db instances are
   * related in a parent-child relationship to the original instance so that events are correctly emitted on child
   * db instances. Child db instances are cached so performing db('db1') twice will return the same instance.
   * You can control these behaviors with the options noListener and returnNonCachedInstance.
   *
   * @method
   * @param {string} name The name of the database we want to use.
   * @param {object} [options=null] Optional settings.
   * @param {boolean} [options.noListener=false] Do not make the db an event listener to the original connection.
   * @param {boolean} [options.returnNonCachedInstance=false] Control if you want to return a cached instance or have a new one created
   * @return {Db}
   */
  Db.prototype.db = function(dbName, options) {
    options = options || {};
    // Copy the options and add out internal override of the not shared flag
    for(var key in this.options) {
      options[key] = this.options[key];
    }
  
    // Do we have the db in the cache already
    if(this.s.dbCache[dbName] && options.returnNonCachedInstance !== true) {
      return this.s.dbCache[dbName];
    }
  
    // Add current db as parentDb
    if(options.noListener == null || options.noListener == false) {
      options.parentDb = this;
    }
  
    // Add promiseLibrary
    options.promiseLibrary = this.s.promiseLibrary;
  
    // Return the db object
    var db = new Db(dbName, this.s.topology, options)
  
    // Add as child
    if(options.noListener == null || options.noListener == false) {
      this.addChild(db);
    }
  
    // Add the db to the cache
    this.s.dbCache[dbName] = db;
    // Return the database
    return db;
  };
  
  define.classMethod('db', {callback: false, promise:false, returns: [Db]});
  
  var _executeAuthCreateUserCommand = function(self, username, password, options, callback) {
    // Special case where there is no password ($external users)
    if(typeof username == 'string'
      && password != null && typeof password == 'object') {
      options = password;
      password = null;
    }
  
    // Unpack all options
    if(typeof options == 'function') {
      callback = options;
      options = {};
    }
  
    // Error out if we digestPassword set
    if(options.digestPassword != null) {
      throw toError("The digestPassword option is not supported via add_user. Please use db.command('createUser', ...) instead for this option.");
    }
  
    // Get additional values
    var customData = options.customData != null ? options.customData : {};
    var roles = Array.isArray(options.roles) ? options.roles : [];
    var maxTimeMS = typeof options.maxTimeMS == 'number' ? options.maxTimeMS : null;
  
    // If not roles defined print deprecated message
    if(roles.length == 0) {
      console.log("Creating a user without roles is deprecated in MongoDB >= 2.6");
    }
  
    // Get the error options
    var commandOptions = {writeCommand:true};
    if(options['dbName']) commandOptions.dbName = options['dbName'];
  
    // Add maxTimeMS to options if set
    if(maxTimeMS != null) commandOptions.maxTimeMS = maxTimeMS;
  
    // Check the db name and add roles if needed
    if((self.databaseName.toLowerCase() == 'admin' || options.dbName == 'admin') && !Array.isArray(options.roles)) {
      roles = ['root']
    } else if(!Array.isArray(options.roles)) {
      roles = ['dbOwner']
    }
  
    // Build the command to execute
    var command = {
        createUser: username
      , customData: customData
      , roles: roles
      , digestPassword:false
    }
  
    // Apply write concern to command
    command = writeConcern(command, self, options);
  
    // Use node md5 generator
    var md5 = crypto.createHash('md5');
    // Generate keys used for authentication
    md5.update(username + ":mongo:" + password);
    var userPassword = md5.digest('hex');
  
    // No password
    if(typeof password == 'string') {
      command.pwd = userPassword;
    }
  
    // Force write using primary
    commandOptions.readPreference = CoreReadPreference.primary;
  
    // Execute the command
    self.command(command, commandOptions, function(err, result) {
      if(err && err.ok == 0 && err.code == undefined) return handleCallback(callback, {code: -5000}, null);
      if(err) return handleCallback(callback, err, null);
      handleCallback(callback, !result.ok ? toError(result) : null
        , result.ok ? [{user: username, pwd: ''}] : null);
    })
  }
  
  var addUser = function(self, username, password, options, callback) {
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
    // Attempt to execute auth command
    _executeAuthCreateUserCommand(self, username, password, options, function(err, r) {
      // We need to perform the backward compatible insert operation
      if(err && err.code == -5000) {
        var finalOptions = writeConcern(shallowClone(options), self, options);
        // Use node md5 generator
        var md5 = crypto.createHash('md5');
        // Generate keys used for authentication
        md5.update(username + ":mongo:" + password);
        var userPassword = md5.digest('hex');
  
        // If we have another db set
        var db = options.dbName ? self.db(options.dbName) : self;
  
        // Fetch a user collection
        var collection = db.collection(Db.SYSTEM_USER_COLLECTION);
  
        // Check if we are inserting the first user
        collection.count({}, function(err, count) {
          // We got an error (f.ex not authorized)
          if(err != null) return handleCallback(callback, err, null);
          // Check if the user exists and update i
          collection.find({user: username}, {dbName: options['dbName']}).toArray(function(err, documents) {
            // We got an error (f.ex not authorized)
            if(err != null) return handleCallback(callback, err, null);
            // Add command keys
            finalOptions.upsert = true;
  
            // We have a user, let's update the password or upsert if not
            collection.update({user: username},{$set: {user: username, pwd: userPassword}}, finalOptions, function(err, results, full) {
              if(count == 0 && err) return handleCallback(callback, null, [{user:username, pwd:userPassword}]);
              if(err) return handleCallback(callback, err, null)
              handleCallback(callback, null, [{user:username, pwd:userPassword}]);
            });
          });
        });
  
        return;
      }
  
      if(err) return handleCallback(callback, err);
      handleCallback(callback, err, r);
    });
  }
  
  /**
   * Add a user to the database.
   * @method
   * @param {string} username The username.
   * @param {string} password The password.
   * @param {object} [options=null] Optional settings.
   * @param {(number|string)} [options.w=null] The write concern.
   * @param {number} [options.wtimeout=null] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {object} [options.customData=null] Custom data associated with the user (only Mongodb 2.6 or higher)
   * @param {object[]} [options.roles=null] Roles associated with the created user (only Mongodb 2.6 or higher)
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.addUser = function(username, password, options, callback) {
    // Unpack the parameters
    var self = this;
    var args = Array.prototype.slice.call(arguments, 2);
    callback = args.pop();
    if(typeof callback != 'function') args.push(callback);
    options = args.length ? args.shift() || {} : {};
  
    // If we have a callback fallback
    if(typeof callback == 'function') return addUser(self, username, password, options, callback);
  
    // Return a promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      addUser(self, username, password, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  define.classMethod('addUser', {callback: true, promise:true});
  
  var _executeAuthRemoveUserCommand = function(self, username, options, callback) {
    if(typeof options == 'function') callback = options, options = {};
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
    // Get the error options
    var commandOptions = {writeCommand:true};
    if(options['dbName']) commandOptions.dbName = options['dbName'];
  
    // Get additional values
    var maxTimeMS = typeof options.maxTimeMS == 'number' ? options.maxTimeMS : null;
  
    // Add maxTimeMS to options if set
    if(maxTimeMS != null) commandOptions.maxTimeMS = maxTimeMS;
  
    // Build the command to execute
    var command = {
      dropUser: username
    }
  
    // Apply write concern to command
    command = writeConcern(command, self, options);
  
    // Force write using primary
    commandOptions.readPreference = CoreReadPreference.primary;
  
    // Execute the command
    self.command(command, commandOptions, function(err, result) {
      if(err && !err.ok && err.code == undefined) return handleCallback(callback, {code: -5000});
      if(err) return handleCallback(callback, err, null);
      handleCallback(callback, null, result.ok ? true : false);
    })
  }
  
  var removeUser = function(self, username, options, callback) {
    // Attempt to execute command
    _executeAuthRemoveUserCommand(self, username, options, function(err, result) {
      if(err && err.code == -5000) {
        var finalOptions = writeConcern(shallowClone(options), self, options);
        // If we have another db set
        var db = options.dbName ? self.db(options.dbName) : self;
  
        // Fetch a user collection
        var collection = db.collection(Db.SYSTEM_USER_COLLECTION);
  
        // Locate the user
        collection.findOne({user: username}, {}, function(err, user) {
          if(user == null) return handleCallback(callback, err, false);
          collection.remove({user: username}, finalOptions, function(err, result) {
            handleCallback(callback, err, true);
          });
        });
  
        return;
      }
  
      if(err) return handleCallback(callback, err);
      handleCallback(callback, err, result);
    });
  }
  
  define.classMethod('removeUser', {callback: true, promise:true});
  
  /**
   * Remove a user from a database
   * @method
   * @param {string} username The username.
   * @param {object} [options=null] Optional settings.
   * @param {(number|string)} [options.w=null] The write concern.
   * @param {number} [options.wtimeout=null] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.removeUser = function(username, options, callback) {
    // Unpack the parameters
    var self = this;
    var args = Array.prototype.slice.call(arguments, 1);
    callback = args.pop();
    if(typeof callback != 'function') args.push(callback);
    options = args.length ? args.shift() || {} : {};
  
    // If we have a callback fallback
    if(typeof callback == 'function') return removeUser(self, username, options, callback);
  
    // Return a promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      removeUser(self, username, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  var authenticate = function(self, username, password, options, callback) {
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
    // the default db to authenticate against is 'self'
    // if authententicate is called from a retry context, it may be another one, like admin
    var authdb = options.authdb ? options.authdb : options.dbName;
    authdb = options.authSource ? options.authSource : authdb;
    authdb = authdb ? authdb : self.databaseName;
  
    // Callback
    var _callback = function(err, result) {
      if(self.listeners('authenticated').length > 0) {
        self.emit('authenticated', err, result);
      }
  
      // Return to caller
      handleCallback(callback, err, result);
    }
  
    // authMechanism
    var authMechanism = options.authMechanism || '';
    authMechanism = authMechanism.toUpperCase();
  
    // If classic auth delegate to auth command
    if(authMechanism == 'MONGODB-CR') {
      self.s.topology.auth('mongocr', authdb, username, password, function(err, result) {
        if(err) return handleCallback(callback, err, false);
        _callback(null, true);
      });
    } else if(authMechanism == 'PLAIN') {
      self.s.topology.auth('plain', authdb, username, password, function(err, result) {
        if(err) return handleCallback(callback, err, false);
        _callback(null, true);
      });
    } else if(authMechanism == 'MONGODB-X509') {
      self.s.topology.auth('x509', authdb, username, password, function(err, result) {
        if(err) return handleCallback(callback, err, false);
        _callback(null, true);
      });
    } else if(authMechanism == 'SCRAM-SHA-1') {
      self.s.topology.auth('scram-sha-1', authdb, username, password, function(err, result) {
        if(err) return handleCallback(callback, err, false);
        _callback(null, true);
      });
    } else if(authMechanism == 'GSSAPI') {
      if(process.platform == 'win32') {
        self.s.topology.auth('sspi', authdb, username, password, options, function(err, result) {
          if(err) return handleCallback(callback, err, false);
          _callback(null, true);
        });
      } else {
        self.s.topology.auth('gssapi', authdb, username, password, options, function(err, result) {
          if(err) return handleCallback(callback, err, false);
          _callback(null, true);
        });
      }
    } else if(authMechanism == 'DEFAULT') {
      self.s.topology.auth('default', authdb, username, password, function(err, result) {
        if(err) return handleCallback(callback, err, false);
        _callback(null, true);
      });
    } else {
      handleCallback(callback, MongoError.create({message: f("authentication mechanism %s not supported", options.authMechanism), driver:true}));
    }
  }
  
  /**
   * Authenticate a user against the server.
   * @method
   * @param {string} username The username.
   * @param {string} [password] The password.
   * @param {object} [options=null] Optional settings.
   * @param {string} [options.authMechanism=MONGODB-CR] The authentication mechanism to use, GSSAPI, MONGODB-CR, MONGODB-X509, PLAIN
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.authenticate = function(username, password, options, callback) {
    if(typeof options == 'function') callback = options, options = {};
    var self = this;
    // Shallow copy the options
    options = shallowClone(options);
  
    // Set default mechanism
    if(!options.authMechanism) {
      options.authMechanism = 'DEFAULT';
    } else if(options.authMechanism != 'GSSAPI'
      && options.authMechanism != 'MONGODB-CR'
      && options.authMechanism != 'MONGODB-X509'
      && options.authMechanism != 'SCRAM-SHA-1'
      && options.authMechanism != 'PLAIN') {
        return handleCallback(callback, MongoError.create({message: "only GSSAPI, PLAIN, MONGODB-X509, SCRAM-SHA-1 or MONGODB-CR is supported by authMechanism", driver:true}));
    }
  
    // If we have a callback fallback
    if(typeof callback == 'function') return authenticate(self, username, password, options, function(err, r) {
      // Support failed auth method
      if(err && err.message && err.message.indexOf('saslStart') != -1) err.code = 59;
      // Reject error
      if(err) return callback(err, r);
      callback(null, r);
    });
  
    // Return a promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      authenticate(self, username, password, options, function(err, r) {
        // Support failed auth method
        if(err && err.message && err.message.indexOf('saslStart') != -1) err.code = 59;
        // Reject error
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  define.classMethod('authenticate', {callback: true, promise:true});
  
  /**
   * Logout user from server, fire off on all connections and remove all auth info
   * @method
   * @param {object} [options=null] Optional settings.
   * @param {string} [options.dbName=null] Logout against different database than current.
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.logout = function(options, callback) {
    var self = this;
    var args = Array.prototype.slice.call(arguments, 0);
    callback = args.pop();
    if(typeof callback != 'function') args.push(callback);
    options = args.length ? args.shift() || {} : {};
  
    // logout command
    var cmd = {'logout':1};
  
    // Add onAll to login to ensure all connection are logged out
    options.onAll = true;
  
    // We authenticated against a different db use that
    if(this.s.authSource) options.dbName = this.s.authSource;
  
    // Execute the command
    if(typeof callback == 'function') return this.command(cmd, options, function(err, result) {
      // Did the user destroy the topology
      if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
      if(err) return handleCallback(callback, err, false);
      handleCallback(callback, null, true)
    });
  
    // Return promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      self.command(cmd, options, function(err, result) {
        // Did the user destroy the topology
        if(self.serverConfig && self.serverConfig.isDestroyed()) return reject(new MongoError('topology was destroyed'));
        if(err) return reject(err);
        resolve(true);
      });
    });
  }
  
  define.classMethod('logout', {callback: true, promise:true});
  
  // Figure out the read preference
  var getReadPreference = function(options, db) {
    if(options.readPreference) return options;
    if(db.readPreference) options.readPreference = db.readPreference;
    return options;
  }
  
  /**
   * Retrieves this collections index info.
   * @method
   * @param {string} name The name of the collection.
   * @param {object} [options=null] Optional settings.
   * @param {boolean} [options.full=false] Returns the full raw index information.
   * @param {(ReadPreference|string)} [options.readPreference=null] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {Db~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Db.prototype.indexInformation = function(name, options, callback) {
    var self = this;
    if(typeof options == 'function') callback = options, options = {};
    options = options || {};
  
    // If we have a callback fallback
    if(typeof callback == 'function') return indexInformation(self, name, options, callback);
  
    // Return a promise
    return new this.s.promiseLibrary(function(resolve, reject) {
      indexInformation(self, name, options, function(err, r) {
        if(err) return reject(err);
        resolve(r);
      });
    });
  };
  
  var indexInformation = function(self, name, options, callback) {
      // If we specified full information
    var full = options['full'] == null ? false : options['full'];
  
    // Did the user destroy the topology
    if(self.serverConfig && self.serverConfig.isDestroyed()) return callback(new MongoError('topology was destroyed'));
  
    // Process all the results from the index command and collection
    var processResults = function(indexes) {
      // Contains all the information
      var info = {};
      // Process all the indexes
      for(var i = 0; i < indexes.length; i++) {
        var index = indexes[i];
        // Let's unpack the object
        info[index.name] = [];
        for(var name in index.key) {
          info[index.name].push([name, index.key[name]]);
        }
      }
  
      return info;
    }
  
    // Get the list of indexes of the specified collection
    self.collection(name).listIndexes().toArray(function(err, indexes) {
      if(err) return callback(toError(err));
      if(!Array.isArray(indexes)) return handleCallback(callback, null, []);
      if(full) return handleCallback(callback, null, indexes);
      handleCallback(callback, null, processResults(indexes));
    });
  }
  
  define.classMethod('indexInformation', {callback: true, promise:true});
  
  var createCreateIndexCommand = function(db, name, fieldOrSpec, options) {
    var indexParameters = parseIndexOptions(fieldOrSpec);
    var fieldHash = indexParameters.fieldHash;
    var keys = indexParameters.keys;
  
    // Generate the index name
    var indexName = typeof options.name == 'string' ? options.name : indexParameters.name;
    var selector = {
      'ns': db.databaseName + "." + name, 'key': fieldHash, 'name': indexName
    }
  
    // Ensure we have a correct finalUnique
    var finalUnique = options == null || 'object' === typeof options ? false : options;
    // Set up options
    options = options == null || typeof options == 'boolean' ? {} : options;
  
    // Add all the options
    var keysToOmit = Object.keys(selector);
    for(var optionName in options) {
      if(keysToOmit.indexOf(optionName) == -1) {
        selector[optionName] = options[optionName];
      }
    }
  
    if(selector['unique'] == null) selector['unique'] = finalUnique;
  
    // Remove any write concern operations
    var removeKeys = ['w', 'wtimeout', 'j', 'fsync', 'readPreference'];
    for(var i = 0; i < removeKeys.length; i++) {
      delete selector[removeKeys[i]];
    }
  
    // Return the command creation selector
    return selector;
  }
  
  var createIndexUsingCreateIndexes = function(self, name, fieldOrSpec, options, callback) {
    // Build the index
    var indexParameters = parseIndexOptions(fieldOrSpec);
    // Generate the index name
    var indexName = typeof options.name == 'string' ? options.name : indexParameters.name;
    // Set up the index
    var indexes = [{ name: indexName, key: indexParameters.fieldHash }];
    // merge all the options
    var keysToOmit = Object.keys(indexes[0]);
    for(var optionName in options) {
      if(keysToOmit.indexOf(optionName) == -1) {
        indexes[0][optionName] = options[optionName];
      }
  
      // Remove any write concern operations
      var removeKeys = ['w', 'wtimeout', 'j', 'fsync', 'readPreference'];
      for(var i = 0; i < removeKeys.length; i++) {
        delete indexes[0][removeKeys[i]];
      }
    }
  
    // Create command
    var cmd = {createIndexes: name, indexes: indexes};
  
    // Apply write concern to command
    cmd = writeConcern(cmd, self, options);
  
    // Build the command
    self.command(cmd, options, function(err, result) {
      if(err) return handleCallback(callback, err, null);
      if(result.ok == 0) return handleCallback(callback, toError(result), null);
      // Return the indexName for backward compatibility
      handleCallback(callback, null, indexName);
    });
  }
  
  // Validate the database name
  var validateDatabaseName = function(databaseName) {
    if(typeof databaseName !== 'string') throw MongoError.create({message: "database name must be a string", driver:true});
    if(databaseName.length === 0) throw MongoError.create({message: "database name cannot be the empty string", driver:true});
    if(databaseName == '$external') return;
  
    var invalidChars = [" ", ".", "$", "/", "\\"];
    for(var i = 0; i < invalidChars.length; i++) {
      if(databaseName.indexOf(invalidChars[i]) != -1) throw MongoError.create({message: "database names cannot contain the character '" + invalidChars[i] + "'", driver:true});
    }
  }
  
  // Get write concern
  var writeConcern = function(target, db, options) {
    if(options.w != null || options.j != null || options.fsync != null) {
      var opts = {};
      if(options.w) opts.w = options.w;
      if(options.wtimeout) opts.wtimeout = options.wtimeout;
      if(options.j) opts.j = options.j;
      if(options.fsync) opts.fsync = options.fsync;
      target.writeConcern = opts;
    } else if(db.writeConcern.w != null || db.writeConcern.j != null || db.writeConcern.fsync != null) {
      target.writeConcern = db.writeConcern;
    }
  
    return target
  }
  
  // Add listeners to topology
  var createListener = function(self, e, object) {
    var listener = function(err) {
      if(e != 'error') {
        object.emit(e, err, self);
  
        // Emit on all associated db's if available
        for(var i = 0; i < self.s.children.length; i++) {
          self.s.children[i].emit(e, err, self.s.children[i]);
        }
      }
    }
    return listener;
  }
  
  /**
   * Db close event
   *
   * Emitted after a socket closed against a single server or mongos proxy.
   *
   * @event Db#close
   * @type {MongoError}
   */
  
  /**
   * Db authenticated event
   *
   * Emitted after all server members in the topology (single server, replicaset or mongos) have successfully authenticated.
   *
   * @event Db#authenticated
   * @type {object}
   */
  
  /**
   * Db reconnect event
   *
   *  * Server: Emitted when the driver has reconnected and re-authenticated.
   *  * ReplicaSet: N/A
   *  * Mongos: Emitted when the driver reconnects and re-authenticates successfully against a Mongos.
   *
   * @event Db#reconnect
   * @type {object}
   */
  
  /**
   * Db error event
   *
   * Emitted after an error occurred against a single server or mongos proxy.
   *
   * @event Db#error
   * @type {MongoError}
   */
  
  /**
   * Db timeout event
   *
   * Emitted after a socket timeout occurred against a single server or mongos proxy.
   *
   * @event Db#timeout
   * @type {MongoError}
   */
  
  /**
   * Db parseError event
   *
   * The parseError event is emitted if the driver detects illegal or corrupt BSON being received from the server.
   *
   * @event Db#parseError
   * @type {MongoError}
   */
  
  /**
   * Db fullsetup event, emitted when all servers in the topology have been connected to at start up time.
   *
   * * Server: Emitted when the driver has connected to the single server and has authenticated.
   * * ReplSet: Emitted after the driver has attempted to connect to all replicaset members.
   * * Mongos: Emitted after the driver has attempted to connect to all mongos proxies.
   *
   * @event Db#fullsetup
   * @type {Db}
   */
  
  // Constants
  Db.SYSTEM_NAMESPACE_COLLECTION = "system.namespaces";
  Db.SYSTEM_INDEX_COLLECTION = "system.indexes";
  Db.SYSTEM_PROFILE_COLLECTION = "system.profile";
  Db.SYSTEM_USER_COLLECTION = "system.users";
  Db.SYSTEM_COMMAND_COLLECTION = "$cmd";
  Db.SYSTEM_JS_COLLECTION = "system.js";
  
  module.exports = Db;
  