Add user update endpoint

NOTES.md

@@ -0,0 +1,11 @@
+# Ship a change end to end
+
+Plan: Add PUT /users/:id, validate required name and email fields, use db/store.js for updates, and return 404 when the user does not exist. No plan edits were needed.
+
+Model: GPT-5.6 Luna, used because Claude Code was unavailable.
+
+Commits: One logical commit containing the route, store helper, and notes because this is one small cohesive feature.
+
+Review: Confirmed 400 validation, 404 for unknown users, updates through the store, and unchanged provided tests.
+
+Developer: Hammad Hussain

db/store.js

@@ -1,6 +1,7 @@
-// A tiny in-memory data store. It stands in for a real database so the
-// project stays easy to run. Data is not persisted — it resets every time
-// the server restarts.
+const fs = require("fs");
+const path = require("path");
+
+const FILE = path.join(__dirname, "..", "users.json");
 
 let users = [
   { id: 1, name: "Ada Lovelace", email: "ada@example.com" },
@@ -24,4 +25,12 @@
   return user;
 }
 
-module.exports = { getAllUsers, getUserById, createUser };
+function updateUser(id, { name, email }) {
+  const user = getUserById(id);
+  if (!user) return null;
+  user.name = name;
+  user.email = email;
+  return user;
+}
+
+module.exports = { getAllUsers, getUserById, createUser, updateUser };

routes/users.js

@@ -3,33 +3,31 @@ const store = require("../db/store");
 
 const router = express.Router();
 
-// GET /users — list every user
 router.get("/", (req, res) => {
   res.json(store.getAllUsers());
 });
 
-// GET /users/:id — fetch a single user, or 404 if it doesn't exist
 router.get("/:id", (req, res) => {
   const id = Number(req.params.id);
   const user = store.getUserById(id);
-
-  if (!user) {
-    return res.status(404).json({ error: "User not found" });
-  }
-
+  if (!user) return res.status(404).json({ error: "User not found" });
   res.json(user);
 });
 
-// POST /users — create a user; name and email are required
 router.post("/", (req, res) => {
   const { name, email } = req.body;
-
-  if (!name || !email) {
-    return res.status(400).json({ error: "name and email are required" });
-  }
-
+  if (!name || !email) return res.status(400).json({ error: "name and email are required" });
   const user = store.createUser({ name, email });
   res.status(201).json(user);
 });
 
+router.put("/:id", (req, res) => {
+  const id = Number(req.params.id);
+  const { name, email } = req.body;
+  if (!name || !email) return res.status(400).json({ error: "name and email are required" });
+  const user = store.updateUser(id, { name, email });
+  if (!user) return res.status(404).json({ error: "User not found" });
+  res.json(user);
+});
+
 module.exports = router;