Add PUT /users/:id update-user endpoint

NOTES.md

@@ -0,0 +1,9 @@
+The original plan outlined the necessary steps: the updates to routes/users.js and db/store.js. It wanted to write NOTES.ms itself, but I told it not to do it - the task was that I write it myself. I also made sure each step is committed one by one, without pushes in the beginning. I also added a prompt for a small stylistic change to the code it suggested.
+
+I decided to go on with Sonnet. I think this implementation does not need heavy lifting to use Opus, but is critical enough to avoid using Haiku.
+
+I went with one commit/one logical change. I did not push it deliberately until all tests passed.
+
+It found a duplicated condition check, which I told it to refactor since I love clean code.
+
+Added this extra line to reopen pull request, as the platform could not check it first

db/store.js

@@ -24,4 +24,17 @@ function createUser({ name, email }) {
   return user;
 }
 
-module.exports = { getAllUsers, getUserById, createUser };
+function updateUser(id, { name, email }) {
+  const user = getUserById(id);
+
+  if (!user) {
+    return undefined;
+  }
+
+  user.name = name;
+  user.email = email;
+
+  return user;
+}
+
+module.exports = { getAllUsers, getUserById, createUser, updateUser };

routes/users.js

@@ -3,6 +3,10 @@ const store = require("../db/store");
 
 const router = express.Router();
 
+function hasRequiredFields({ name, email }) {
+  return !!name && !!email;
+}
+
 // GET /users — list every user
 router.get("/", (req, res) => {
   res.json(store.getAllUsers());
@@ -24,12 +28,30 @@ router.get("/:id", (req, res) => {
 router.post("/", (req, res) => {
   const { name, email } = req.body;
 
-  if (!name || !email) {
+  if (!hasRequiredFields({ name, email })) {
     return res.status(400).json({ error: "name and email are required" });
   }
 
   const user = store.createUser({ name, email });
   res.status(201).json(user);
 });
 
+// PUT /users/:id — update an existing user; name and email are required
+router.put("/:id", (req, res) => {
+  const id = Number(req.params.id);
+  const { name, email } = req.body;
+
+  if (!hasRequiredFields({ 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;