var util = require('./util');
var express = require('express');
var http = require('http');
var EventEmitter = require('events').EventEmitter;
var WebSocketServer = require('ws').Server;
var url = require('url');



function PeerServer(options) {
  if (!(this instanceof PeerServer)) return new PeerServer(options);
  EventEmitter.call(this);

  this._app = express();
  this._httpServer = http.createServer(this._app);
  this._app.use(express.bodyParser());
  this._app.use(this._allowCrossDomain);

  this._options = util.extend({
    port: 80,
    debug: false,
    timeout: 5000
  }, options);

  util.debug = this._options.debug;

  // Listen on user-specified port and create WebSocket server as well.
  this._httpServer.listen(this._options.port);
  this._wss = new WebSocketServer({ path: '/ws', server: this._httpServer });

  // WebSockets that are opened or HTTP responses (which are paired with
  // something in timeouts.
  this._clients = {};
  // Timeouts for HTTP responses.
  this._timeouts = {};
  // Connections waiting for another peer.
  this._outstandingOffers = {};

  // Initailize WebSocket server handlers.
  this._initializeWSS();

  // Initialize HTTP routes. This is only used for the first few milliseconds
  // before a socket is opened for a Peer.
  this._initializeHTTP();
};

util.inherits(PeerServer, EventEmitter);

/** Handle CORS */
PeerServer.prototype._allowCrossDomain = function(req, res, next) {
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type');

  next();
}

/** Initialize WebSocket server. */
PeerServer.prototype._initializeWSS = function() {
  var self = this;
  this._wss.on('connection', function(socket) {
    var id = url.parse(socket.upgradeReq.url, true).query.id;
    if (!!id && !!self._clients[id]) {
      // If response client and timeout exist, overwrite and clear.
      if (!!self._timeouts[id]) {
        clearTimeout(self._timeouts[id]);
        delete self._timeouts[id];
        self._clients[id].end(JSON.stringify({ type: 'HTTP-SOCKET' }));
      } else {
        socket.send(JSON.stringify({ type: 'ID-TAKEN', msg: 'ID is taken' }));
        socket.close();
        return;
      }
    } else if (id === undefined) {
      id = self._generateClientId();
    }
    socket.send(JSON.stringify({ type: 'OPEN', id: id }));

    // Save the socket for this id.
    self._clients[id] = socket;

    self._processOutstandingOffers(id);

    // Cleanup after a socket closes.
    socket.on('close', function() {
      util.log('Socket closed:', id);
      self._removePeer(id);
    });
    // Handle messages from peers.
    socket.on('message', function(data) {
      try {
        var message = JSON.parse(data);
        util.log(message);

        switch (message.type) {
          case 'LEAVE':
            // Clean up if a Peer sends a LEAVE.
            if (!message.dst) {
              self._removePeer(id);
              break;
            }
          // ICE candidates
          case 'CANDIDATE':
          // Offer or answer between peers.
          case 'OFFER':
          case 'ANSWER':
          // Firefoxism (connectDataConnection ports)
          case 'PORT':
            // Use the ID we know to be correct to prevent spoofing.
            message.src = id;
            self._handleTransmission(message);
            break;
          default:
            util.prettyError('Message unrecognized');
        }
      } catch(e) {
        util.log('Invalid message', data);
      }
    });
  });
};


/** Process outstanding peer offers. */
PeerServer.prototype._processOutstandingOffers = function(id) {
  var offers = this._outstandingOffers[id];
  if (offers === undefined) {
    return;
  }
  var sources = Object.keys(offers);
  for (var i = 0, ii = sources.length; i < ii; i += 1) {
    var messages = offers[sources[i]];
    for (var j = 0, jj = messages.length; j < jj; j += 1) {
      this._handleTransmission.apply(this, messages[j]);
    }
    delete this._outstandingOffers[id][sources[i]];
  }
};

/** Initialize HTTP server routes. */
PeerServer.prototype._initializeHTTP = function() {
  var self = this;

  this._app.options('/*', function(req, res, next) {
    res.send(200);
  });

  // Server sets up HTTP streaming whether you get or post an ID.
  // Retrieve guaranteed random ID.
  this._app.get('/id', function(req, res) {
    var clientId = util.randomId();
    while (!!self._clients[clientId]) {
      clientId = util.randomId();
    }
    self._startStreaming(res, clientId, function() {
      // Chrome hacks.
      res.write('{"id":"' + clientId + '"}\n');
    });
  });

  this._app.post('/id', function(req, res) {
    var id = req.body.id;
    self._startStreaming(res, id);
  });

  this._app.post('/offer', function(req, res) {
    self._handleTransmission(req.body, res);
  });

  this._app.post('/candidate', function(req, res) {
    self._handleTransmission(req.body, res);
  });

  this._app.post('/answer', function(req, res) {
    self._handleTransmission(req.body, res);
  });

  this._app.post('/leave', function(req, res) {
    self._handleTransmission(req.body, res);
  });

  this._app.post('/port', function(req, res) {
    self._handleTransmission(req.body, res);
  });
};

PeerServer.prototype._removePeer = function(id) {
  delete this._clients[id];
  if (this._timeouts[id]) {
    clearTimeout(this._timeouts[id]);
    delete this._timeouts[id];
  }
};

/** Saves a streaming response and takes care of timeouts and headers. */
PeerServer.prototype._startStreaming = function(res, id, write) {
  res.writeHead(200, {'Content-Type': 'application/octet-stream'});
  if (!!write) {
    write();
  }

  var pad = '00';
  var iterations = 10;
  for (var i = 0; i < iterations; i++) {
    pad += pad;
  }
  res.write(pad + '\n');

  // Save res so we can write to it.
  if (!this._clients[id]) {
    this._clients[id] = res;
    // Set timeout to expire.
    var self = this;
    this._timeouts[id] = setTimeout(function() {
      self._removePeer(id);
      res.end(JSON.stringify({ type: 'HTTP-END' }));
    }, 30000);
    this._processOutstandingOffers(id);
  } else {
    res.end(JSON.stringify({ type: 'HTTP-ERROR' }));
  }

};

/** Handles passing on a message. */
PeerServer.prototype._handleTransmission = function(message, res) {
  var type = message.type;
  var src = message.src;
  var dst = message.dst;
  var data = JSON.stringify(message);

  var destination = this._clients[dst];

  if (!!destination) {
    try {
      if (this._timeouts[dst]) {
        data += '\n';
        destination.write(data);
      } else {
        destination.send(data);
      }
      if (!!res) {
        res.send(200);
      }
    } catch (e) {
      // This happens when a peer disconnects without closing connections and
      // the associated WebSocket has not closed.
      util.prettyError(e);
      // Tell other side to stop trying.
      this._removePeer(dst);
      this._handleTransmission({
        type: 'LEAVE',
        src: dst,
        dst: src
      });
      if (!!res) res.send(501);
    }
  } else {
    // Wait 5 seconds for this client to connect/reconnect (XHR) for important
    // messages.
    if (type !== 'LEAVE') {
      var self = this;
      if (!this._outstandingOffers[dst]) {
        this._outstandingOffers[dst] = {};
      }
      if (!this._outstandingOffers[dst][src]) {
        this._outstandingOffers[dst][src] = [];
        setTimeout(function() {
          if(!!self._outstandingOffers[dst][src]) {
            delete self._outstandingOffers[dst][src];
            self._handleTransmission({
              type: 'EXPIRE',
              src: dst,
              dst: src
            });
          }
        }, this._options.timeout);
      }
      this._outstandingOffers[dst][src].push([message]);
      if (!!res) res.send(200);
    } else if (type === 'LEAVE' && !dst) {
      this._removePeer(src);
      if (!!res) res.send(200);
    } else if (src) {
      // Assume a disconnect if the client no longer exists.
      // Unless it's a message from the server.
      this._handleTransmission({
        type: 'EXPIRE',
        src: dst,
        dst: src
      });
      // 410: Resource not available.
      if (!!res) res.send(410);
    }
  }
};

PeerServer.prototype._generateClientId = function() {
  var clientId = util.randomId();
  while (!!this._clients[clientId]) {
    clientId = util.randomId();
  }
  return clientId;
};

exports.PeerServer = PeerServer;