Add tags field to todos and ?tag= filter on GET /todos

- Add tags:[] to all seed todo objects
- POST /todos accepts optional tags array (defaults to [])
- GET /todos?tag=<value> filters to todos whose tags include that value (case-sensitive)

Closes #14

index.js

@@ -0,0 +1,52 @@
+const express = require('express');
+const { name, version } = require('./package.json');
+
+const app = express();
+const PORT = 3000;
+
+app.use(express.json());
+
+let todos = [
+  { id: 1, title: 'Buy groceries', done: false, tags: [] },
+  { id: 2, title: 'Walk the dog', done: true, tags: [] },
+  { id: 3, title: 'Read a book', done: false, tags: [] },
+];
+
+let nextId = 4;
+
+app.get('/healthz', (req, res) => {
+  res.json({ ok: true });
+});
+
+app.get('/version', (req, res) => {
+  res.json({ name, version });
+});
+
+app.get('/todos', (req, res) => {
+  const { tag } = req.query;
+  if (tag !== undefined) {
+    return res.json(todos.filter(t => t.tags.includes(tag)));
+  }
+  res.json(todos);
+});
+
+app.post('/todos', (req, res) => {
+  const { title, tags } = req.body;
+  const todo = { id: nextId++, title, done: false, tags: Array.isArray(tags) ? tags : [] };
+  todos.push(todo);
+  res.status(201).json(todo);
+});
+
+app.delete('/todos/:id', (req, res) => {
+  const id = parseInt(req.params.id, 10);
+  const index = todos.findIndex(t => t.id === id);
+  if (index === -1) {
+    return res.status(404).end();
+  }
+  todos.splice(index, 1);
+  res.status(204).end();
+});
+
+app.listen(PORT, () => {
+  console.log(`Server listening on http://localhost:${PORT}`);
+});