/*!
 * router
 * Copyright(c) 2013 Roman Shtylman
 * Copyright(c) 2014 Douglas Christopher Wilson
 * MIT Licensed
 */

'use strict'

/**
 * Module dependencies.
 * @private
 */

var debug = require('debug')('router')
var flatten = require('array-flatten')
var methods = require('methods')
var mixin = require('utils-merge')
var parseUrl = require('parseurl')
var setPrototypeOf = require('setprototypeof')
var Layer = require('./lib/layer')
var Route = require('./lib/route')

/**
 * Module variables.
 * @private
 */

var slice = Array.prototype.slice

/* istanbul ignore next */
var defer = typeof setImmediate === 'function'
  ? setImmediate
  : function(fn){ process.nextTick(fn.bind.apply(fn, arguments)) }

/**
 * Expose `Router`.
 */

module.exports = Engine
module.exports.Route = Route
module.exports.sanitizeUse = sanitizeUse
module.exports.methods = methods.concat('all')

/**
 * Initialize a new `Router` with the given `options`.
 *
 * @param {object} options
 * @return {Router} which is an callable function
 * @public
 */

function Engine(options) {
  var opts = options || {}

  function router(req, res, next) {
    router.handle(req, res, next)
  }

  // inherit from the correct prototype
  setPrototypeOf(router, this)

  router.mergeParams = opts.mergeParams
  router.params = {}
  router.stack = []

  return router
}

/**
 * Engine prototype inherits from a Function.
 */

Engine.prototype = Object.create(Function.prototype)

/**
 * Allow the `Layer` and `Route` to be overriden in child implementations.
 */
Engine.prototype.Layer = Layer
Engine.prototype.Route = Route

/**
 * Map the given param placeholder `name`(s) to the given callback.
 *
 * Parameter mapping is used to provide pre-conditions to routes
 * which use normalized placeholders. For example a _:user_id_ parameter
 * could automatically load a user's information from the database without
 * any additional code.
 *
 * The callback uses the same signature as middleware, the only difference
 * being that the value of the placeholder is passed, in this case the _id_
 * of the user. Once the `next()` function is invoked, just like middleware
 * it will continue on to execute the route, or subsequent parameter functions.
 *
 * Just like in middleware, you must either respond to the request or call next
 * to avoid stalling the request.
 *
 *  router.param('user_id', function(req, res, next, id){
 *    User.find(id, function(err, user){
 *      if (err) {
 *        return next(err)
 *      } else if (!user) {
 *        return next(new Error('failed to load user'))
 *      }
 *      req.user = user
 *      next()
 *    })
 *  })
 *
 * @param {string} name
 * @param {function} fn
 * @public
 */

Engine.prototype.param = function param(name, fn) {
  if (!name) {
    throw new TypeError('argument name is required')
  }

  if (typeof name !== 'string') {
    throw new TypeError('argument name must be a string')
  }

  if (!fn) {
    throw new TypeError('argument fn is required')
  }

  if (typeof fn !== 'function') {
    throw new TypeError('argument fn must be a function')
  }

  var params = this.params[name]

  if (!params) {
    params = this.params[name] = []
  }

  params.push(fn)

  return this
}

/**
 * Dispatch a req, res into the router.
 *
 * @private
 */

Engine.prototype.handle = function handle(req, res, callback) {
  if (!callback) {
    throw new TypeError('argument callback is required')
  }

  debug('dispatching %s %s', req.method, req.url)

  var idx = 0
  var methods
  var protohost = getProtohost(req.url) || ''
  var removed = ''
  var self = this
  var slashAdded = false
  var paramcalled = {}

  // middleware and routes
  var stack = this.stack

  // manage inter-router variables
  var parentParams = req.params
  var parentUrl = req.baseUrl || ''
  var done = restore(callback, req, 'baseUrl', 'next', 'params')

  // setup next layer
  req.next = next

  // for options requests, respond with a default if nothing else responds
  if (req.method === 'OPTIONS') {
    methods = []
    done = wrap(done, generateOptionsResponder(res, methods))
  }

  // setup basic req values
  req.baseUrl = parentUrl
  req.originalUrl = req.originalUrl || req.url

  next()

  function next(err) {
    var layerError = err === 'route' || err === 'router'
      ? null
      : err

    // remove added slash
    if (slashAdded) {
      req.url = req.url.substr(1)
      slashAdded = false
    }

    // restore altered req.url
    if (removed.length !== 0) {
      req.baseUrl = parentUrl
      req.url = protohost + removed + req.url.substr(protohost.length)
      removed = ''
    }

    // no more matching layers
    if (err === 'router' || idx >= stack.length) {
      defer(done, layerError)
      return
    }

    // get pathname of request
    var path = getPathname(req)

    if (path == null) {
      return done(layerError)
    }

    // find next matching layer
    var layer
    var match
    var route

    while (!match && idx < stack.length) {
      layer = stack[idx++]
      match = layer.match(path, req, res)
      route = layer.route

      if (!match) {
        continue
      }

      if (!route) {
        // process non-route handlers normally
        continue
      }

      if (layerError) {
        // routes do not match with a pending error
        match = false
        continue
      }

      var method = req.method
      var has_method = route._handles_method(method)

      // build up automatic options response
      if (!has_method && method === 'OPTIONS' && methods) {
        methods.push.apply(methods, route._methods())
      }

      // don't even bother matching route
      if (!has_method && method !== 'HEAD') {
        match = false
        continue
      }
    }

    // no match
    if (!match) {
      return done(layerError)
    }

    var layerPath = match.path
    var layerParams = decodeLayerParams(match.params)

    if (layerParams instanceof Error) {
      return done(layerParams)
    }

    // store route for dispatch on change
    if (route) {
      req.route = route
    }

    // Capture one-time layer values
    req.params = self.mergeParams
      ? mergeParams(layerParams, parentParams)
      : layerParams

    // this should be done for the layer
    self.process_params(match, paramcalled, req, res, function (err) {
      if (err) {
        return next(layerError || err)
      }

      if (route) {
        return layer.handle_request(req, res, next)
      }

      trim_prefix(layer, layerError, layerPath, path)
    })
  }

  function trim_prefix(layer, layerError, layerPath, path) {
    var c = path[layerPath.length]

    if (c && c !== '/') {
      next(layerError)
      return
    }

     // Trim off the part of the url that matches the route
     // middleware (.use stuff) needs to have the path stripped
    if (layerPath.length !== 0) {
      debug('trim prefix (%s) from url %s', layerPath, req.url)
      removed = layerPath
      req.url = protohost + req.url.substr(protohost.length + removed.length)

      // Ensure leading slash
      if (!protohost && req.url[0] !== '/') {
        req.url = '/' + req.url
        slashAdded = true
      }

      // Setup base URL (no trailing slash)
      req.baseUrl = parentUrl + (removed[removed.length - 1] === '/'
        ? removed.substring(0, removed.length - 1)
        : removed)
    }

    debug('%s %s : %s', layer.name, layerPath, req.originalUrl)

    if (layerError) {
      layer.handle_error(layerError, req, res, next)
    } else {
      layer.handle_request(req, res, next)
    }
  }
}

/**
 * Process any parameters for the layer.
 *
 * @private
 */

Engine.prototype.process_params = function process_params(match, called, req, res, done) {
  var params = this.params

  // captured parameters from the layer, keys and values
  var keys = match.params && Object.keys(match.params)

  // fast track
  if (!keys || keys.length === 0) {
    return done()
  }

  var i = 0
  var paramIndex = 0
  var key
  var paramVal
  var paramCallbacks
  var paramCalled

  // process params in order
  // param callbacks can be async
  function param(err) {
    if (err) {
      return done(err)
    }

    if (i >= keys.length ) {
      return done()
    }

    paramIndex = 0
    key = keys[i++]

    if (!key) {
      return done()
    }

    paramVal = req.params[key]
    paramCallbacks = params[key]
    paramCalled = called[key]

    if (paramVal === undefined || !paramCallbacks) {
      return param()
    }

    // param previously called with same value or error occurred
    if (paramCalled && (paramCalled.match === paramVal
      || (paramCalled.error && paramCalled.error !== 'route'))) {
      // restore value
      req.params[key] = paramCalled.value

      // next param
      return param(paramCalled.error)
    }

    called[key] = paramCalled = {
      error: null,
      match: paramVal,
      value: paramVal
    }

    paramCallback()
  }

  // single param callbacks
  function paramCallback(err) {
    var fn = paramCallbacks[paramIndex++]

    // store updated value
    paramCalled.value = req.params[key]

    if (err) {
      // store error
      paramCalled.error = err
      param(err)
      return
    }

    if (!fn) return param()

    try {
      fn(req, res, paramCallback, paramVal, key)
    } catch (e) {
      paramCallback(e)
    }
  }

  param()
}

/**
 * Use the given middleware function, with optional path, defaulting to "/".
 *
 * Use (like `.all`) will run for any http METHOD, but it will not add
 * handlers for those methods so OPTIONS requests will not consider `.use`
 * functions even if they could respond.
 *
 * The other difference is that _route_ path is stripped and not visible
 * to the handler function. The main effect of this feature is that mounted
 * handlers can operate without any code changes regardless of the "prefix"
 * pathname.
 *
 * @public
 */

Engine.prototype.use = function use(path, match, handlers) {
  if (!path) {
    throw new TypeError('argument path is required')
  }

  if (!match) {
    throw new TypeError('argument match is required')
  }

  if (typeof match !== 'function') {
    throw new TypeError('argument match must be a function')
  }

  if (!Array.isArray(handlers) || handlers.length === 0) {
    throw new TypeError('argument handler is required')
  }

  var layerMatch = path === '/' ? fast_slash : match

  for (var i = 0; i < handlers.length; i++) {
    var fn = handlers[i]

    if (typeof fn !== 'function') {
      throw new TypeError('argument handler must be a function')
    }

    // add the middleware
    debug('use %s %s', path, fn.name || '<anonymous>')

    var layer = new this.Layer(path, layerMatch, fn)
    layer.route = undefined
    this.stack.push(layer)
  }

  return this
}

/**
 * Create a new Route for the given path.
 *
 * Each route contains a separate middleware stack and VERB handlers.
 *
 * See the Route api documentation for details on adding handlers
 * and middleware to routes.
 *
 * @param {function} path
 * @return {Route}
 * @public
 */

Engine.prototype.route = function route(path, match) {
  if (!path) {
    throw new TypeError('argument path is required')
  }

  if (!match) {
    throw new TypeError('argument match is required')
  }

  if (typeof match !== 'function') {
    throw new TypeError('argument match must be a function')
  }

  var route = new this.Route(path)
  var layer = new this.Layer(path, match, handle)

  function handle(req, res, next) {
    route.dispatch(req, res, next)
  }

  layer.route = route

  this.stack.push(layer)

  return route
}

/**
 * Generate a callback that will make an OPTIONS response.
 *
 * @param {OutgoingMessage} res
 * @param {array} methods
 * @private
 */

function generateOptionsResponder(res, methods) {
  return function onDone(fn, err) {
    if (err || methods.length === 0) {
      return fn(err)
    }

    trySendOptionsResponse(res, methods, fn)
  }
}

/**
 * Get pathname of request.
 *
 * @param {IncomingMessage} req
 * @private
 */

function getPathname(req) {
  try {
    return parseUrl(req).pathname
  } catch (err) {
    return undefined
  }
}

/**
 * Get get protocol + host for a URL.
 *
 * @param {string} url
 * @private
 */

function getProtohost(url) {
  if (url.length === 0 || url[0] === '/') {
    return undefined
  }

  var searchIndex = url.indexOf('?')
  var pathLength = searchIndex !== -1
    ? searchIndex
    : url.length
  var fqdnIndex = url.substr(0, pathLength).indexOf('://')

  return fqdnIndex !== -1
    ? url.substr(0, url.indexOf('/', 3 + fqdnIndex))
    : undefined
}

/**
 * Merge params with parent params
 *
 * @private
 */

function mergeParams(params, parent) {
  if (typeof parent !== 'object' || !parent) {
    return params
  }

  // make copy of parent for base
  var obj = mixin({}, parent)

  // simple non-numeric merging
  if (!(0 in params) || !(0 in parent)) {
    return mixin(obj, params)
  }

  var i = 0
  var o = 0

  // determine numeric gap in params
  while (i in params) {
    i++
  }

  // determine numeric gap in parent
  while (o in parent) {
    o++
  }

  // offset numeric indices in params before merge
  for (i--; i >= 0; i--) {
    params[i + o] = params[i]

    // create holes for the merge when necessary
    if (i < o) {
      delete params[i]
    }
  }

  return mixin(obj, params)
}

/**
 * Restore obj props after function
 *
 * @private
 */

function restore(fn, obj) {
  var props = new Array(arguments.length - 2)
  var vals = new Array(arguments.length - 2)

  for (var i = 0; i < props.length; i++) {
    props[i] = arguments[i + 2]
    vals[i] = obj[props[i]]
  }

  return function(err){
    // restore vals
    for (var i = 0; i < props.length; i++) {
      obj[props[i]] = vals[i]
    }

    return fn.apply(this, arguments)
  }
}

/**
 * Send an OPTIONS response.
 *
 * @private
 */

function sendOptionsResponse(res, methods) {
  var options = Object.create(null)

  // build unique method map
  for (var i = 0; i < methods.length; i++) {
    options[methods[i]] = true
  }

  // construct the allow list
  var allow = Object.keys(options).sort().join(', ')

  // send response
  res.setHeader('Allow', allow)
  res.setHeader('Content-Length', Buffer.byteLength(allow))
  res.setHeader('Content-Type', 'text/plain')
  res.setHeader('X-Content-Type-Options', 'nosniff')
  res.end(allow)
}

/**
 * Try to send an OPTIONS response.
 *
 * @private
 */

function trySendOptionsResponse(res, methods, next) {
  try {
    sendOptionsResponse(res, methods)
  } catch (err) {
    next(err)
  }
}

/**
 * Wrap a function
 *
 * @private
 */

function wrap(old, fn) {
  return function proxy() {
    var args = new Array(arguments.length + 1)

    args[0] = old
    for (var i = 0, len = arguments.length; i < len; i++) {
      args[i + 1] = arguments[i]
    }

    fn.apply(this, args)
  }
}

/**
 * Attempt to decode layer parameters
 */

function decodeLayerParams(params) {
  try {
    return decodeParams(params)
  } catch (err) {
    return err
  }
}

/**
 * Decode all param values
 *
 * @param {object} params
 * @return {object}
 */

function decodeParams(params) {
  var decodedParams = {}

  if (params) {
    var keys = Object.keys(params)

    for (var i = 0; i < keys.length; i++) {
      var key = keys[i]

      decodedParams[key] = decodeParam(params[key])
    }
  }

  return decodedParams
}

/**
 * Decode param value
 *
 * @param {string} val
 * @return {string}
 * @api private
 */

function decodeParam(val){
  if (typeof val !== 'string' || val.length === 0) {
    return val
  }

  try {
    return decodeURIComponent(val)
  } catch (err) {
    if (err instanceof URIError) {
      err.message = 'Failed to decode param \'' + val + '\''
      err.status = 400
    }

    throw err
  }
}

/**
 * Helper for sanitizing `Router.prototype.use` arguments.
 */

function sanitizeUse(handler) {
  var offset = 0
  var path = '/'

  // default path to '/'
  // disambiguate router.use([handler])
  if (handler != null && typeof handler !== 'function') {
    var arg = handler

    while (Array.isArray(arg) && arg.length !== 0) {
      arg = arg[0]
    }

    // first arg is the path
    if (typeof arg !== 'function') {
      offset = 1
      path = handler
    }
  }

  var callbacks = flatten(slice.call(arguments, offset))

  return { path: path, callbacks: callbacks }
}

/**
 * Always return path match.
 */

function fast_slash () {
  return { path: '' }
}
