server.js

var express = require('express');

var app = express();

var port = process.env.PORT || 3000;

app.use('/', express.static('./client'));

var server = app.listen(port);

var io = require('socket.io')({
  transports: ["xhr-polling"],
  'polling duration': 10
}).listen(server);

var users = {};
var queue = [];
var votes = {};
var upvotes = 0;
var downvotes = 0;
var current;
var timeTotal;
var timeLeft;
var sync;
var set;
var switched;

//Helper function to reset the state of clients connected
var reset = function() {
  votes = {};
  upvotes = 0;
  downvotes = 0;
  io.emit('clearVotes');
  io.emit('nextVideo', current);
  io.emit('setQueue', queue);
}

io.on('connection', function(socket) {

  //Receives username from client and emits username, socket id, users online back to client
  socket.on('username', function(username) {
    if (!userExist(users, username) || username === 'anonymous'){
      io.emit('chatMessage', {username: "", message: username + " has joined"});
    }
    users[socket.id] = username;
    io.sockets.connected[socket.id].emit('setUser', username);
    io.sockets.connected[socket.id].emit('setId', socket.id);
    io.emit('usersOnline', users);
  });

  //Sends queue information to client
  socket.on('getQueue', function() {
    if (queue.length) {
      io.sockets.connected[socket.id].emit('setQueue', queue);
    }
  });

  //Sends current video to client
  socket.on('getCurrent', function() {
    if (current) {
      io.sockets.connected[socket.id].emit('setCurrent', current);
    } else {
      io.sockets.connected[socket.id].emit('setVolume');
    }
  });

  //Sends vote information for current video to client
  socket.on('getVotes', function() {
    io.sockets.connected[socket.id].emit('changeVotes', {up: upvotes, down: downvotes});
  });

  //Sends video duration to client
  socket.on('getTime', function() {
    io.sockets.connected[socket.id].emit('setTime', timeTotal - timeLeft || timeTotal);
  });

  //Emits message to all clients
  socket.on('sendMessage', function(data) {
    io.emit('chatMessage', data);
  });

  //Emits alert message only to sender
  socket.on('sendAlert', function(data) {
    socket.emit('chatMessage', data);
  });

  //Emits data to only specific client (private message)
  socket.on('privateMessage', function(data){
    io.sockets.sockets[data.sendToSocketId].emit('chatMessage', data);
    socket.emit('chatMessage', data);
  });

  //Send error message to user on submit
  socket.on('errorMessage', function(data){
    socket.emit('chatMessage', data);
  });

  //Check if user exists
  socket.on('checkUser', function(username){
    var exist = false;
    for (var key in users){
      if (users[key] === username){
        exist = true;
      }
    }
    socket.emit('userExist', exist);
  });

  function userExist(object, username){
    for (var key in object){
      if (users[key] === username){
        return true;
      }
    }
    return false;
  }

  socket.on('enqueue', function(data) {
    if (current) {

      queue.push(data);
      io.emit('addVideo', data);

    } else {
      set = false;
      current = data;
      reset();
    }
  });

  socket.on('dequeue', function(data) {
    var id = socket.id;

    if (id.slice(2) === data.socket) {
      io.emit('removeVideo', data.id);
    }
  });

  socket.on('updateQueue', function(data) {
    queue = data;
    socket.broadcast.emit('refreshQueue', queue);
  });

  socket.on('easterEgg', function() {
    if (queue.length) {
      queue.unshift({ id: 'SbyZDq76T74', 
                      title: 'Meow Mix song', 
                      username: 'Meow Mode', 
                      socket: current.socket });
      current = queue.shift();
      reset();

    } else {
      current = { id: 'SbyZDq76T74', 
                  title: 'Meow Mix song', 
                  username: 'Meow Mode', 
                  socket: socket.id.slice(2) };
      reset();
    }
  });

  //Receives video ended from client and sets current to next in queue
  //Jerry-rigged so that the fastest client emits the switch and locks other clients out for 5 seconds
  socket.on('ended', function() {
    if (!switched) {
      switched = true;
      set = false;
      current = queue.shift();
      reset();
      setTimeout(function() {
        switched = false;
      }, 5000);
    }
  });

  //Allows skipping if event is emitted by client who enqueued video
  socket.on('skip', function(easterEgg) {
    var id = socket.id;
    if (current && id.slice(2) === current.socket || easterEgg) {

      if (queue.length) {
        set = false;
        current = queue.shift();
        reset();
      } else {
        set= false;
        current = null;
        reset();
        io.emit('stopVideo');
      }
    }
  });

  //Start the video sync clock
  socket.on('setDuration', function(duration) {
    if (!set) {
      set = true;
      timeTotal = duration;
      timeLeft = duration;
      clearInterval(sync);
      sync = setInterval(function() {
        timeLeft--;
        if (timeLeft === 0) {
          clearInterval(sync);
        }
      }, 1000);
    }
  });

  //Removes client vote information and delete client on client disconnect
  socket.on('disconnect', function() {
    if (votes[socket.id] === 'up') {
      upvotes--;
    }

    if (votes[socket.id] === 'down') {
      downvotes--;
    }

    io.emit('changeVotes', {up: upvotes, down: downvotes});

    io.emit('chatMessage', {username: "", message: users[socket.id] + " has left"});

    delete users[socket.id];

    io.emit('usersOnline', users);
  });

  //Receives upvote from client and updates vote information; emitting to all clients
  socket.on('upVote', function() {
    if (votes[socket.id] === 'down') {
      votes[socket.id] = 'up';
      downvotes--;
      upvotes++;
    }

    if (votes[socket.id] === undefined) {
      votes[socket.id] = 'up';
      upvotes++;
    }

    io.emit('changeVotes', {up: upvotes, down: downvotes});
  });

  socket.on('downVote', function(){
    if(votes[socket.id] === 'up'){
      votes[socket.id] = 'down';
      upvotes--;
      downvotes++;
    }

    if(votes[socket.id] === undefined) {
      votes[socket.id] = 'down';
      downvotes++;
    }

    //Skips current video if more haters than non-haters
    var haters = downvotes/Object.keys(users).length;

    if(haters > 0.5) {
      if (queue.length) {
        set = false;
        current = queue.shift();
        reset();
      } else {
        set= false;
        current = null;
        reset();
        io.emit('stopVideo');
      }
    }
    
    io.emit('changeVotes', {up: upvotes, down: downvotes});
  });

  //Sends clock time to client when requested
  socket.on('getSync', function() {
    io.sockets.connected[socket.id].emit('setSync', timeTotal - timeLeft || timeTotal);
  });

});