index.js

const express = require("express");
const app = express();
const http = require("http").Server(app);
const io = require("socket.io")(http);
const port = process.env.PORT || 3000;

app.use(express.static(__dirname + "/public"));

app.get("/", function (req, res) {
  res.sendFile("index.html", { root: __dirname });
});

app.get("/ai", function (req, res) {
  res.sendFile("ai.html", { root: __dirname });
});

app.get("/online", function (req, res) {
  var rand = Math.random().toString(36).slice(2);
  res.redirect("/online/" + rand);
});

app.get("/online/*", function (req, res) {
  res.sendFile("online.html", { root: __dirname });
});

io.on("connection", function (socket) {
  var referer = socket.handshake.headers.referer.split("/");
  var rand = referer[referer.length - 1];

  socket.join(rand);
  var room = io.sockets.adapter.rooms[rand];

  if (!room.game) {
    room.game = {
      players: [],
      history: [],
    };
  }

  if (room.game.players.length === 0) {
    if (Math.random() < 0.5) {
      socket.player = "X";
    } else {
      socket.player = "O";
    }
  } else if (room.game.players.indexOf("X") === -1) {
    socket.player = "X";
  } else if (room.game.players.indexOf("O") === -1) {
    socket.player = "O";
  } else {
    socket.player = null;
  }

  if (socket.player) {
    room.game.players.push(socket.player);
  }

  socket.emit("connection", socket.player, room);
  io.to(rand).emit("someone connected", room);

  socket.on("move", (move) => {
    room.game.history.push(move);
    socket.broadcast.to(rand).emit("move", move);
  });

  socket.on("disconnect", () => {
    if (socket.player) {
      var i = room.game.players.indexOf(socket.player);
      room.game.players.splice(i, 1);
    }
    io.to(rand).emit("someone disconnected", room);
  });
});

http.listen(port, () => {
  console.log("listening on *:" + port);
});