/**
 * Module dependencies.
 */

var qs = require('querystring')
  , parse = require('url').parse
  , readFileSync = require('fs').readFileSync
  , crypto = require('crypto')
  , base64id = require('base64id')
  , transports = require('./transports')
  , EventEmitter = require('events').EventEmitter
  , Socket = require('./socket')
  , WebSocketServer = require('ws').Server
  , debug = require('debug')('engine');

/**
 * Module exports.
 */

module.exports = Server;

/**
 * Server constructor.
 *
 * @param {Object} options
 * @api public
 */

function Server(opts){
  if (!(this instanceof Server)) {
    return new Server(opts);
  }

  this.clients = {};
  this.clientsCount = 0;

  opts = opts || {};
  this.pingTimeout = opts.pingTimeout || 60000;
  this.pingInterval = opts.pingInterval || 25000;
  this.upgradeTimeout = opts.upgradeTimeout || 10000;
  this.maxHttpBufferSize = opts.maxHttpBufferSize || 10E7;
  this.transports = opts.transports || Object.keys(transports);
  this.allowUpgrades = false !== opts.allowUpgrades;
  this.allowRequest = opts.allowRequest;
  this.cookie = false !== opts.cookie ? (opts.cookie || 'io') : false;

  // initialize websocket server
  if (~this.transports.indexOf('websocket')) {
    this.ws = new WebSocketServer({ noServer: true, clientTracking: false });
  }
}

/**
 * Protocol errors mappings.
 */

Server.errors = {
  UNKNOWN_TRANSPORT: 0,
  UNKNOWN_SID: 1,
  BAD_HANDSHAKE_METHOD: 2,
  BAD_REQUEST: 3
};

Server.errorMessages = {
  0: 'Transport unknown',
  1: 'Session ID unknown',
  2: 'Bad handshake method',
  3: 'Bad request'
};

/**
 * Inherits from EventEmitter.
 */

Server.prototype.__proto__ = EventEmitter.prototype;

/**
 * Hash of open clients.
 *
 * @api public
 */

Server.prototype.clients;

/**
 * Returns a list of available transports for upgrade given a certain transport.
 *
 * @return {Array}
 * @api public
 */

Server.prototype.upgrades = function(transport){
  if (!this.allowUpgrades) return [];
  return transports[transport].upgradesTo || [];
};

/**
 * Verifies a request.
 *
 * @param {http.ServerRequest}
 * @return {Boolean} whether the request is valid
 * @api private
 */

Server.prototype.verify = function(req, upgrade, fn){
  // transport check
  var transport = req._query.transport;
  if (!~this.transports.indexOf(transport)) {
    debug('unknown transport "%s"', transport);
    return fn(Server.errors.UNKNOWN_TRANSPORT, false);
  }

  // sid check
  var sid = req._query.sid;
  if (sid) {
    if (!this.clients.hasOwnProperty(sid))
      return fn(Server.errors.UNKNOWN_SID, false);
    if (!upgrade && this.clients[sid].transport.name !== transport) {
      debug('bad request: unexpected transport without upgrade');
      return fn(Server.errors.BAD_REQUEST, false);
    }
  } else {
    // handshake is GET only
    if ('GET' != req.method) return fn(Server.errors.BAD_HANDSHAKE_METHOD, false);
    if (!this.allowRequest) return fn(null, true);
    return this.allowRequest(req, fn);
  }

  fn(null, true);
};

/**
 * Prepares a request by processing the query string.
 *
 * @api private
 */

Server.prototype.prepare = function(req){
  // try to leverage pre-existing `req._query` (e.g: from connect)
  if (!req._query) {
    req._query = ~req.url.indexOf('?') ? qs.parse(parse(req.url).query) : {};
  }
};

/**
 * Closes all clients.
 *
 * @api public
 */

Server.prototype.close = function(){
  debug('closing all open clients');
  for (var i in this.clients) {
    this.clients[i].close();
  }
  return this;
};

/**
 * Handles an Engine.IO HTTP request.
 *
 * @param {http.ServerRequest} request
 * @param {http.ServerResponse|http.OutgoingMessage} response
 * @api public
 */

Server.prototype.handleRequest = function(req, res){
  debug('handling "%s" http request "%s"', req.method, req.url);
  this.prepare(req);
  req.res = res;

  var self = this;
  this.verify(req, false, function(err, success) {
    if (!success) {
      sendErrorMessage(req, res, err);
      return;
    }

    if (req._query.sid) {
      debug('setting new request for existing client');
      self.clients[req._query.sid].transport.onRequest(req);
    } else {
      self.handshake(req._query.transport, req);
    }
  });
};

/**
 * Sends an Engine.IO Error Message
 *
 * @param {http.ServerResponse} response
 * @param {code} error code
 * @api private
 */

 function sendErrorMessage(req, res, code) {
    var headers = { 'Content-Type': 'application/json' };

    if (req.headers.origin) {
      headers['Access-Control-Allow-Credentials'] = 'true';
      headers['Access-Control-Allow-Origin'] = req.headers.origin;
    } else {
      headers['Access-Control-Allow-Origin'] = '*';
    }
    res.writeHead(400, headers);
    res.end(JSON.stringify({
      code: code,
      message: Server.errorMessages[code]
    }));
 }

/**
 * Handshakes a new client.
 *
 * @param {String} transport name
 * @param {Object} request object
 * @api private
 */

Server.prototype.handshake = function(transport, req){
  var id = base64id.generateId();

  debug('handshaking client "%s"', id);

  var transportName = transport;
  try {
    var transport = new transports[transport](req);
    if ('polling' == transportName) {
      transport.maxHttpBufferSize = this.maxHttpBufferSize;
    }

    if (req._query && req._query.b64) {
      transport.supportsBinary = false;
    } else {
      transport.supportsBinary = true;
    }
  }
  catch (e) {
    sendErrorMessage(req, req.res, Server.errors.BAD_REQUEST);
    return;
  }
  var socket = new Socket(id, this, transport, req);
  var self = this;

  if (false !== this.cookie) {
    transport.on('headers', function(headers){
      headers['Set-Cookie'] = self.cookie + '=' + id;
    });
  }

  transport.onRequest(req);

  this.clients[id] = socket;
  this.clientsCount++;

  socket.once('close', function(){
    delete self.clients[id];
    self.clientsCount--;
  });

  this.emit('connection', socket);
};

/**
 * Handles an Engine.IO HTTP Upgrade.
 *
 * @api public
 */

Server.prototype.handleUpgrade = function(req, socket, upgradeHead){
  this.prepare(req);

  var self = this;
  this.verify(req, true, function(err, success) {
    if (!success) {
      socket.end();
      return;
    }

    var head = new Buffer(upgradeHead.length);
    upgradeHead.copy(head);
    upgradeHead = null;

    // delegate to ws
    self.ws.handleUpgrade(req, socket, head, function(conn){
      self.onWebSocket(req, conn);
    });
  });
};

/**
 * Called upon a ws.io connection.
 *
 * @param {ws.Socket} websocket
 * @api private
 */

Server.prototype.onWebSocket = function(req, socket){
  if (!transports[req._query.transport].prototype.handlesUpgrades) {
    debug('transport doesnt handle upgraded requests');
    socket.close();
    return;
  }

  // get client id
  var id = req._query.sid;

  // keep a reference to the ws.Socket
  req.websocket = socket;

  if (id) {
    if (!this.clients[id]) {
      debug('upgrade attempt for closed client');
      socket.close();
    } else if (this.clients[id].upgraded) {
      debug('transport had already been upgraded');
      socket.close();
    } else {
      debug('upgrading existing transport');
      var transport = new transports[req._query.transport](req);
      if (req._query && req._query.b64) {
        transport.supportsBinary = false;
      } else {
        transport.supportsBinary = true;
      }
      this.clients[id].maybeUpgrade(transport);
    }
  } else {
    this.handshake(req._query.transport, req);
  }
};

/**
 * Captures upgrade requests for a http.Server.
 *
 * @param {http.Server} server
 * @param {Object} options
 * @api public
 */

Server.prototype.attach = function(server, options){
  var self = this;
  var options = options || {};
  var path = (options.path || '/engine.io').replace(/\/$/, '');

  var destroyUpgrade = (options.destroyUpgrade !== undefined) ? options.destroyUpgrade : true;
  var destroyUpgradeTimeout = options.destroyUpgradeTimeout || 1000;

  // normalize path
  path += '/';

  function check (req) {
    return path == req.url.substr(0, path.length);
  }

  // cache and clean up listeners
  var listeners = server.listeners('request').slice(0);
  server.removeAllListeners('request');
  server.on('close', self.close.bind(self));

  // add request handler
  server.on('request', function(req, res){
    if (check(req)) {
      debug('intercepting request for path "%s"', path);
      self.handleRequest(req, res);
    } else {
      for (var i = 0, l = listeners.length; i < l; i++) {
        listeners[i].call(server, req, res);
      }
    }
  });

  if(~self.transports.indexOf('websocket')) {
    server.on('upgrade', function (req, socket, head) {
      if (check(req)) {
        self.handleUpgrade(req, socket, head);
      } else if (false !== options.destroyUpgrade) {
        // default node behavior is to disconnect when no handlers
        // but by adding a handler, we prevent that
        // and if no eio thing handles the upgrade
        // then the socket needs to die!
        setTimeout(function() {
           if (socket.writable && socket.bytesWritten <= 0) {
             return socket.end();
           }
        }, options.destroyUpgradeTimeout);
      }
    });
  }
};