server.js

// server.js
// where your node app starts

///////////////////////
//https://www.npmjs.com/package/btoa
function btoa(str) {
  var buffer;

  if (str instanceof Buffer) {
    buffer = str;
  } else {
    buffer = Buffer.from(str.toString(), 'binary');
  }

  return buffer.toString('base64');
}

//https://stackoverflow.com/questions/6274339/how-can-i-shuffle-an-array
function arrShuffle(a) {
    var j, x, i;
    for (i = a.length - 1; i > 0; i--) {
        j = Math.floor(Math.random() * (i + 1));
        x = a[i];
        a[i] = a[j];
        a[j] = x;
    }
    return a;
}

////////////


var SUIT = ["diamond","club","heart","spade"]
var RANK = ["A","7","8","9","10","J","Q","K"]
//var RANK = ["A","2","3","4","5","6","7","8","9","10","J","Q","K"]
var SYMBOLS = {diamond:"♦",club:"♣",heart:"♥",spade:"♠"}
var COLORS = {diamond:"red",club:"black",heart:"red",spade:"black"}
var cards = [];
var CARD_WIDTH = 50;
var CARD_HEIGHT = 70;
var WIDTH = 800;
var HEIGHT = 800;

function randId(){
  return btoa((""+Math.random()).slice(2));
}

function newDeck() {

  var deck = []
  for (var i = 0; i < 4; i++){
    for (var j = 0; j < 8; j++){
      deck.push({
        suit:SUIT[i], 
        rank:RANK[j], 
        x: 0, 
        y: 0, z:0,
        targ: {x:0,y:0},
        resolve_dl: 0,
      })
    }
  }
  deck.push({suit:"red",rank:"joker", 
             x:0, y:0, z:0, resolve_dl: 0,
             targ: {x:0,y:0}});
  // deck.push({suit:"black",rank:"joker",
  //            x: 0, y: 0, z:0, resolve_dl: 0,
  //            targ: {x:0,y:0}});
  function makeId(card){
    return card.suit+"-"+card.rank+"-"+randId();
  }
  for (var i = 0; i < deck.length; i++){
    deck[i].id = makeId(deck[i]);
  }
  shuffleDeck(deck);
  return deck;
}

function shuffleDeck(deck){
  arrShuffle(deck);
  for (var i = 0; i < deck.length; i++){
    deck[i].x = WIDTH/2+10+CARD_HEIGHT/2+i*1;
    deck[i].y = HEIGHT/2-i*1;
    deck[i].z = i;
  }
}

function getCardById(cards,id){
  for (var i = 0; i < cards.length; i++){
    if (cards[i].id == id){
      return cards[i];
    }
  }
}



////////////////////


var express = require('express'); 
var app = express();
var server = app.listen(process.env.PORT || 300);
app.use(express.static('public'));
console.log('server running')

var io = require('socket.io')(server);


var welcome_messages = [
  "welcome to card-server",
  "where multiple persons can mess around with the same deck of cards online",
  "click and drag on a card to move it, or click and drag a selection to move multiple cards",
  // "create or go to a room by appending <code>?room=</code> to the URL, or click on one of the suggested links in the <b>Rooms</b> panel",
  "share the URL with your friends to invite them to your room",
]



var rooms = {"lobby":newRoom("lobby")};
serverMessages(rooms.lobby,welcome_messages);

function newRoom(name){
  return {name:name, messages:[], players:{}, cards:newDeck(), empty_time:0};
}

function locatePlayer(id){
  for (var k in rooms){
    if (id in rooms[k].players){
      return k;
    }
  }
}

function updateServerData(data){
  var room = rooms[locatePlayer(data.id)];
  if (room == undefined){
    console.log("err: player id belongs to no room: "+data.id);
    return;
  }
  if (data.op == "movc"){
    console.log("card-move received: ",data);
    for (var i = 0; i < data.cards.length; i++){
      var cd = getCardById(room.cards, data.cards[i]);
      if (cd == undefined){
        console.log("err: moving a card that does not exist",data.cards[i]);
        continue;
      }
      
      cd.x = data.targs[i].x;
      cd.y = data.targs[i].y;
      cd.z = data.targs[i].z;
    }
  
  }else if (data.op == "msg"){
    console.log("msg received:",data);
    room.messages.push(data);
    
  }else if (data.op == "name"){
    room.players[data.id].name = data.text;
    console.log("set name: "+data.id + "="+data.text);
  
  }else if (data.op == "room"){
    if (!(data.text in rooms)){
      rooms[data.text] = newRoom(data.text);
      console.log("new room opened: "+data.text);
    }
    if (locatePlayer(data.id) != data.text){
      rooms[data.text].players[data.id] = room.players[data.id]; 
      delete room.players[data.id];
    }
  }else if (data.op == "shfl"){
    shuffleDeck(room.cards);
    room.messages.push({id:data.id, timestamp:data.timestamp, name:room.players[data.id].name, text:"[SHUFFLE]"});
  }
}

function getDataForClient(id){
  var room = rooms[locatePlayer(id)];
  return Object.assign({}, room, {"room_list":Object.keys(rooms).slice(0,32)});
}

function maintainRooms(){
  for (var k in rooms){
    // console.log(k,Object.keys(rooms[k].players).length);
    if (Object.keys(rooms[k].players).length==0){
      rooms[k].empty_time += 1;
    }else{
      rooms[k].empty_time = 0;
    }
    if (rooms[k].empty_time > 999){
      console.log("closing room due to inactivity: ",k,rooms[k].empty_time);
      if ( k != "lobby"){
        delete rooms[k];
      }else{
        shuffleDeck(rooms[k].cards);
        rooms[k].messages = []
        rooms[k].empty_time = 0;
        serverMessages(rooms[k],welcome_messages);
        console.log("reset",k,rooms[k].empty_time);
      }
    }
  }
  
}

function serverMessages(room, msgs){
  for (var i = 0; i < msgs.length; i++){
    room.messages.push({id:"server message", timestamp:(new Date()).getTime(), name:"", text:msgs[i]});
  }
}


function newConnection(socket){
	console.log('new connection: ' + socket.id);
  socket.on('client-start', onClientStart);
	socket.on('client-update', onClientUpdate);
	socket.on('disconnect', onClientExit);

	function onClientStart(data){
		var added = false;
    var sillyname = socket.id.slice(0,6);
    
    if (data.room != undefined){
      if (!(data.room in rooms)){
        rooms[data.room] = newRoom(data.room);
      }
      var headcnt = Object.keys(rooms[data.room].players).length;
      if (headcnt < 4){
        rooms[data.room].players[socket.id]= ({name:sillyname, idx:headcnt});
        added = true;
      }
      
    }
    if (!added){
      for (var k in rooms){
        var headcnt = Object.keys(rooms[k].players).length;
        if (headcnt < 4){
          rooms[k].players[socket.id]= ({name:sillyname, idx:headcnt});
          added = true;
          break;
        }
      }
    }
    if (!added){
      var randname = "room-"+randId().slice(0,3);
      while (randname in rooms){
        randname = "room-"+randId().slice(0,3);
      }
      rooms[randname] = newRoom(randname);
      rooms[randname].players[socket.id]= ({name:sillyname, idx:0});
    }
    var self_id = socket.id;
    var self_socket = socket;
		setInterval(heartbeat, 200);
		function heartbeat(){
      maintainRooms();
			self_socket.emit('server-update', getDataForClient(self_id));
		} 
	}
  
	function onClientUpdate(data){
    updateServerData(data);
	}
  
	function onClientExit(){
    var room = rooms[locatePlayer(socket.id)];
    if (room != undefined){
      delete room.players[socket.id];
    }
    console.log(socket.id+' disconnected');
	}
}	


io.sockets.on('connection', newConnection);