server.js

const express = require("express");
const http = require("http");
const path = require("path");
const socketIO = require("socket.io");
const { initGame, gameLoop, getUpdateVelocity } = require('./game');
const { FRAME_RATE } = require('./constants');
const { makeid } = require('./utils');

const state = {};
const clientRooms = {};


const app = express();
const server = http.Server(app);
const io = socketIO(server);

app.set("port", 5000);
app.use(express.static(__dirname + "/public"));

app.get("/", function (request, response) {
    response.sendFile(path.join(__dirname + "/public", "index.html"));
});

server.listen(5000, function () {
    console.log("Start server on port 5000")
});

io.on("connection", client => {
    client.on('keydown', handleKeydown);
    client.on('newGame', handleNewGame);
    client.on('joinGame', handleJoinGame);

    // join to existing room
    function handleJoinGame(roomName) {
        const room = io.sockets.adapter.rooms.get(roomName);

        let numClients = 0;
        if (room) {
            numClients = room.size;
        }

        if (numClients === 0) {
            client.emit('unknownCode');
            return;
        } else if (numClients > 1) {
            client.emit('tooManyPlayers');
            return;
        }

        clientRooms[client.id] = roomName;

        client.join(roomName);
        client.number = 2;
        client.emit('init', 2);

        startGameInterval(roomName);
    }

    // new game creating
    function handleNewGame(){
        let roomName = makeid(5);
        clientRooms[client.id] = roomName;
        client.emit('gameCode', roomName);

        state[roomName] = initGame();

        client.join(roomName);
        client.number = 1;
        client.emit('init', 1);
    }

    function handleKeydown(keyCode){
        const roomName = clientRooms[client.id];

        if (!roomName) {
            return;
        }
        try {
            keyCode = parseInt(keyCode);
        } catch (e) {
            console.error(e);
            return;
        }
        const vel = getUpdateVelocity(keyCode);

        if (vel) {
            state[roomName].players[client.number - 1].vel = vel;
        }
    }
});


// game session
function startGameInterval(roomName) {
    const intervalId = setInterval(() => {
        const winner = gameLoop(state[roomName]);

        if (!winner) {
            emitGameState(roomName, state[roomName]);
        } else {
            emitGameOver(roomName, winner);
            state[roomName] = null;
            clearInterval(intervalId);
        }
    }, 2000 / FRAME_RATE);
}

function emitGameState(roomName, state) {
    io.sockets.in(roomName)
        .emit('gameState', JSON.stringify(state));
}

function emitGameOver(roomName, winner) {
    io.sockets.in(roomName)
        .emit('gameOver', JSON.stringify({ winner }));
}