server logic started

.gitignore

@@ -1,2 +1,5 @@
 # NPM modules
-/node_modules
+/node_modules
+
+# NPM cache
+package-lock.json

app.js

@@ -0,0 +1,47 @@
+const path = require('path');
+const helmet = require('helmet');
+const http = require('http');
+const socketIoServer = require('socket.io');
+const express = require('express');
+
+const PORT = parseInt(process.env.PORT) || 3000;
+
+const EV_CONNECT = 'connection';
+const EV_MESSAGE = 'message';
+const EV_CHAT_MESSAGE = 'chat_message';
+const EV_DISCONNECT = 'disconnect';
+
+const app = express();
+const server = http.createServer(app);
+const io = socketIoServer(server);
+
+// Express middlewares
+app.use(helmet());
+app.use(express.static(path.join(__dirname, 'public')));
+
+// Listen for socket connections
+io.on(EV_CONNECT, (socket) => {
+  console.log(`client socket ${socket.id} connected`);
+
+  // Welcome the new user
+  socket.emit(EV_MESSAGE, 'Welcome to NoChat!');
+
+  // Send to all users except the new user
+  socket.broadcast.emit(EV_MESSAGE, 'A user has joined the chat.');
+
+  // When a user disconnects
+  socket.on(EV_DISCONNECT, () => {
+    io.emit(EV_MESSAGE, 'A user has left the chat.');
+  });
+
+  // When a user sends a message
+  socket.on(EV_CHAT_MESSAGE, (message) => {
+    // We broadcast it to every user
+    io.emit(EV_MESSAGE, message);
+  });
+});
+
+// Start Express server
+server.listen(PORT, () => {
+  console.log(`listening on port ${PORT}`);
+});