Step 5: Read, update and delete

const http = require("http");

const todos = [];
let nextId = 1;

function send(res, status, data) {
  res.writeHead(status, { "Content-Type": "application/json" });
  res.end(JSON.stringify(data));
}
function readBody(req) {
  return new Promise((resolve, reject) => {
    let raw = "";
    req.on("data", (chunk) => (raw += chunk));
    req.on("end", () => {
      try {
        resolve(raw ? JSON.parse(raw) : {});
      } catch (err) {
        reject(new Error("Invalid JSON"));
      }
    });
  });
}

function validate(body) {
  if (typeof body.title !== "string" || body.title.trim() === "") return "title is required";
  if (body.title.length > 100) return "title must be 100 characters or fewer";
  return null;
}

async function handle(req, res) {
  try {
    const match = req.url.match(/^\/todos\/(\d+)$/);
    const id = match ? Number(match[1]) : null;

    if (req.method === "GET" && req.url === "/todos") return send(res, 200, todos);

    if (req.method === "POST" && req.url === "/todos") {
      const body = await readBody(req);
      const problem = validate(body);
      if (problem) return send(res, 400, { error: problem });
      const todo = { id: nextId++, title: body.title.trim(), done: false };
      todos.push(todo);
      return send(res, 201, todo);
    }

    if (id !== null) {
      const todo = todos.find((t) => t.id === id);
      if (!todo) return send(res, 404, { error: "Todo not found" });

      if (req.method === "GET") return send(res, 200, todo);
      if (req.method === "PATCH") {
        const body = await readBody(req);
        if (typeof body.done === "boolean") todo.done = body.done;
        if (body.title !== undefined) {
          const problem = validate(body);
          if (problem) return send(res, 400, { error: problem });
          todo.title = body.title.trim();
        }
        return send(res, 200, todo);
      }
      if (req.method === "DELETE") {
        todos.splice(todos.indexOf(todo), 1);
        res.writeHead(204);
        return res.end();
      }
    }
    send(res, 404, { error: "Not found" });
  } catch (err) {
    send(res, 400, { error: err.message });
  }
}

// ---- demo: start on a free port, make a few requests, stop ----
const server = http.createServer(handle);
server.listen(0, async () => {
  const base = `http://localhost:${server.address().port}`;
  const call = async (method, path, body) => {
    const res = await fetch(base + path, { method, body: body ? JSON.stringify(body) : undefined });
    const text = await res.text();
    console.log(method, path, "->", res.status, text || "(empty)");
  };
  await call("POST", "/todos", { title: "Write tests" });
  await call("GET", "/todos/1");
  await call("PATCH", "/todos/1", { done: true });
  await call("PATCH", "/todos/1", { title: "" });
  await call("GET", "/todos/99");
  await call("DELETE", "/todos/1");
  await call("GET", "/todos");
  server.close();
});

POST /todos -> 201 {"id":1,"title":"Write tests","done":false}
GET /todos/1 -> 200 {"id":1,"title":"Write tests","done":false}
PATCH /todos/1 -> 200 {"id":1,"title":"Write tests","done":true}
PATCH /todos/1 -> 400 {"error":"title is required"}
GET /todos/99 -> 404 {"error":"Todo not found"}
DELETE /todos/1 -> 204 (empty)
GET /todos -> 200 []