Add PUT /users/:id endpoint to update a user

CLAUDE.md

@@ -0,0 +1,9 @@
+# CLAUDE.md
+
+## Architecture
+- routes/users.js — the users resource, one route per action
+- db/store.js — the in-memory data helper all routes go through
+- tests/update-user.test.js — the tests
+
+
+

NOTES.md

@@ -0,0 +1,26 @@
+# NOTES.md
+
+## Plan
+Plan the new endpoint "update a user" to 
+
+- update an existing user by id (PUT /users/:id)
+- validate the input, rejecting missing or invalid fields with a clear error
+- return a sensible "not found" response when the user doesn't exist, rather than crashing
+- go through db/store.js for data access, following the existing pattern
+
+The repo already contains the tests for this endpoint, in tests/update-user.test.js. They start red — making them pass is how 
+
+
+## Tasks
+
+[ ] Add the updateUser function to db/store.js
+[ ] Add the PUT /users/:id route to routes/users.js
+[ ] Add input validation (return 400 for missing fields)
+[ ] Add 404 handling for non-existent users
+
+## Commits
+First commit contains changes to db/store.js
+Second commit contains the creation of the new endpoint (+ input validation, 400 and 404 return responses)
+
+## Model
+I will use opusplan

db/store.js

@@ -24,4 +24,16 @@ 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

@@ -32,4 +32,22 @@ router.post("/", (req, res) => {
   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 (!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;