feat: Implement basic chat-app concept

Author: JanefrancessC

chat-app/.gitignore

@@ -0,0 +1 @@
+node_modules/

chat-app/backend/index.js

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+import express from "express";
+import cors from "cors";
+
+const app = express();
+app.use(cors());
+app.use(express.json());
+
+const port = 3000;
+const messages = [
+  {
+    message: "Hello",
+    user: "Jane",
+    time: Date.now() - 6000,
+  },
+  {
+    message: "Hey",
+    user: "John",
+    time: Date.now() - 3000,
+  },
+  {
+    message: "Hi",
+    user: "Bob",
+    time: Date.now(),
+  },
+];
+const callbacksForNewMessages = [];
+
+app.get("/", (req, res) => {
+  res.json({ message: `Welcome to my Chat Application!` });
+});
+
+app.get("/messages", (req, res) => {
+  let since = Number(req.query.since);
+  let longPoll = req.query.longPoll === "true";
+
+  if (since) {
+    const messagesToSend = messages.filter((msg) => msg.time > since);
+    if (messagesToSend.length === 0 && longPoll) {
+      callbacksForNewMessages.push((val) => res.json(val));
+      return;
+    } else res.json(messagesToSend);
+    return;
+  }
+  res.json(messages);
+});
+
+app.post("/messages", (req, res) => {
+  const { message, user } = req.body;
+
+  if (
+    typeof message !== "string" ||
+    typeof user !== "string" ||
+    !message.trim() ||
+    !user.trim()
+  ) {
+    res.status(400).json({ error: `Message and user are required!` });
+    return;
+  }
+
+  messages.push({
+    message,
+    user,
+    time: Date.now(),
+  });
+  while (callbacksForNewMessages.length > 0) {
+    const callback = callbacksForNewMessages.pop();
+    callback([messages[messages.length - 1]]);
+  }
+  res.status(201).json({ success: true });
+});
+
+app.listen(port, () => {
+  console.log(`Chat server listening on port ${port}`);
+});