Implement update user endpoint

Author: lointaiine-cloud

NOTES.md

@@ -0,0 +1,15 @@
+# Notes
+
+## Implementation
+
+Added `PUT /users/:id` to update an existing user by ID. The endpoint validates that both `name` and `email` are provided, returns `400` when either field is missing, returns `404` when the requested user does not exist, and returns the updated user with status `200` on success.
+
+The in-memory store now provides an `updateUser` helper that finds the user, updates its name and email, and returns the updated record.
+
+## Testing
+
+The existing grading tests were left unchanged. The implementation is designed to satisfy the success, missing-user, and missing-field cases covered by those tests.
+
+## Design decision
+
+Validation is performed in the route before calling the store helper, while the store helper is responsible only for locating and updating the user. This keeps HTTP concerns in the route and data operations in the store.

db/store.js

@@ -1,5 +1,5 @@
 // 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
+// project stays easy to run. Data is not persisted — it resets every time
 // the server restarts.
 
 let users = [
@@ -24,4 +24,22 @@ function createUser({ name, email }) {
   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

@@ -3,12 +3,10 @@ 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);
@@ -20,7 +18,6 @@ router.get("/:id", (req, res) => {
   res.json(user);
 });
 
-// POST /users — create a user; name and email are required
 router.post("/", (req, res) => {
   const { name, email } = req.body;
 
@@ -32,4 +29,21 @@ router.post("/", (req, res) => {
   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;