server.js

const express = require("express");
const app = express();
const {Server} = require('socket.io');
const http = require('http'); 
const ACTIONS = require("./src/Actions");
const path = require('path');


const server = http.createServer(app);
const io = new Server(server);

app.use(express.static('build'));
app.use((req,res) => {
    res.sendFile(path.join(__dirname, 'build', 'index.html'));
})

const userSocketMap = {};

function getAllConnectedClients(roomId){
    // MAP
    return Array.from(io.sockets.adapter.rooms.get(roomId) || [] ).map((socketId)=>{
        return {
            socketId,
            username:userSocketMap[socketId],
        }
    });
}

io.on('connection',(socket)=>{
    console.log("User Joined with a socket id : ",socket.id);
    //console.log("socket id:",socket.id , "username: ",);
    //console.log("socket looks like this: ", socket);

    socket.on(ACTIONS.JOIN, ({roomId,username}) => {

        userSocketMap[socket.id] = username; // "socket:id = oeifhofhh" = "username: abcxyz"  -> mapping like this
        socket.join(roomId);
        const clients = getAllConnectedClients(roomId);
        clients.forEach(({socketId}) => {
            io.to(socketId).emit(ACTIONS.JOINED, {
                clients,
                username,
                socketId:socket.id,
            })
        })

    });

    socket.on(ACTIONS.CODE_CHANGE, ({roomId,code}) => {
        socket.in(roomId).emit(ACTIONS.CODE_CHANGE, {code});
    });

    socket.on(ACTIONS.SYNC_CODE, ({socketId,code}) => {
        io.to(socketId).emit(ACTIONS.CODE_CHANGE, {code});
    });

    socket.on('disconnecting', ()=>{
        const rooms = [...socket.rooms];
        rooms.forEach((roomId) => {
            socket.in(roomId).emit(ACTIONS.DISCONNECTED,{
                socketId:socket.id,
                username:userSocketMap[socket.id],
            });
        });
        delete userSocketMap[socket.id];
        socket.leave();
    });
})

const PORT = process.env.PORT || 5000;
server.listen(PORT,()=> console.log(`Listening on port ${PORT}`))