REST API

import { createServer } from "http";
import { URL } from "url";

// ── Data store ─────────────────────────────────────────────────────────────
class TaskStore {
  #tasks = new Map();
  #nextId = 1;

  create({ title, description = "", priority = "medium" }) {
    if (!title?.trim())
      throw Object.assign(new Error("title is required"), { status: 400 });
    if (!["low","medium","high"].includes(priority))
      throw Object.assign(new Error("priority must be low, medium, or high"), { status: 400 });

    const task = {
      id:          this.#nextId++,
      title:       title.trim(),
      description: description.trim(),
      priority,
      completed:   false,
      createdAt:   new Date().toISOString(),
      updatedAt:   new Date().toISOString(),
    };
    this.#tasks.set(task.id, task);
    return task;
  }

  findAll(query = {}) {
    let tasks = [...this.#tasks.values()];
    if (query.completed !== undefined)
      tasks = tasks.filter(t => t.completed === (query.completed === "true"));
    if (query.priority)
      tasks = tasks.filter(t => t.priority === query.priority);
    return tasks;
  }

  findById(id) {
    const task = this.#tasks.get(Number(id));
    if (!task) throw Object.assign(new Error(`Task ${id} not found`), { status: 404 });
    return task;
  }

  update(id, data) {
    const task = this.findById(id);   // throws 404 if not found
    const { id: _id, createdAt, ...allowed } = data;   // prevent overriding id/createdAt
    const updated = { ...task, ...allowed, updatedAt: new Date().toISOString() };
    this.#tasks.set(task.id, updated);
    return updated;
  }

  delete(id) {
    this.findById(id);   // throws 404 if not found
    this.#tasks.delete(Number(id));
  }
}

const store = new TaskStore();

// ── HTTP helpers ───────────────────────────────────────────────────────────
function sendJSON(res, status, body) {
  const json = JSON.stringify(body, null, 2);
  res.writeHead(status, {
    "Content-Type": "application/json; charset=utf-8",
    "Content-Length": Buffer.byteLength(json),
    "Access-Control-Allow-Origin": "*",   // CORS: allow any frontend
  });
  res.end(json);
}

function readJSON(req) {
  return new Promise((resolve, reject) => {
    let data = "";
    req.on("data", chunk => { data += chunk; if (data.length > 1e6) req.destroy(); });
    req.on("end", () => {
      if (!data.trim()) return resolve({});
      try { resolve(JSON.parse(data)); }
      catch { reject(Object.assign(new Error("Invalid JSON"), { status: 400 })); }
    });
    req.on("error", reject);
  });
}

// ── Request router ─────────────────────────────────────────────────────────
const server = createServer(async (req, res) => {
  const { pathname, searchParams } = new URL(req.url, "http://localhost");
  const method  = req.method;
  const query   = Object.fromEntries(searchParams);

  // Match /tasks or /tasks/123
  const tasksRoot  = /^\/tasks\/?$/.test(pathname);
  const tasksById  = /^\/tasks\/(\d+)\/?$/.exec(pathname);
  const id         = tasksById?.[1];

  // Logger
  console.log(`${method} ${pathname}`);

  try {
    // OPTIONS — CORS preflight
    if (method === "OPTIONS") {
      res.writeHead(204, { "Access-Control-Allow-Origin":"*","Access-Control-Allow-Methods":"GET,POST,PATCH,DELETE","Access-Control-Allow-Headers":"Content-Type" });
      return res.end();
    }

    // GET /tasks
    if (method === "GET" && tasksRoot) {
      return sendJSON(res, 200, store.findAll(query));
    }

    // POST /tasks
    if (method === "POST" && tasksRoot) {
      const body = await readJSON(req);
      const task = store.create(body);
      return sendJSON(res, 201, task);
    }

    // GET /tasks/:id
    if (method === "GET" && id) {
      return sendJSON(res, 200, store.findById(id));
    }

    // PATCH /tasks/:id
    if (method === "PATCH" && id) {
      const body    = await readJSON(req);
      const updated = store.update(id, body);
      return sendJSON(res, 200, updated);
    }

    // DELETE /tasks/:id
    if (method === "DELETE" && id) {
      store.delete(id);
      res.writeHead(204);
      return res.end();
    }

    sendJSON(res, 404, { error: "Route not found" });

  } catch (e) {
    sendJSON(res, e.status ?? 500, { error: e.message });
    if (!e.status) console.error(e);
  }
});

server.listen(3000, () => console.log("REST API at http://localhost:3000"));

// Test the TaskStore in isolation — no HTTP needed
class TaskStore {
  #tasks = new Map(); #nextId = 1;
  create({title,description="",priority="medium"}) {
    if(!title?.trim()) throw Object.assign(new Error("title required"),{status:400});
    const t={id:this.#nextId++,title:title.trim(),description,priority,completed:false,
             createdAt:new Date().toISOString(),updatedAt:new Date().toISOString()};
    this.#tasks.set(t.id,t); return t;
  }
  findAll(q={}) {
    let r=[...this.#tasks.values()];
    if(q.completed!==undefined) r=r.filter(t=>t.completed===(q.completed==="true"));
    if(q.priority) r=r.filter(t=>t.priority===q.priority);
    return r;
  }
  findById(id){const t=this.#tasks.get(Number(id));if(!t)throw Object.assign(new Error("not found"),{status:404});return t;}
  update(id,data){const t=this.findById(id);const u={...t,...data,updatedAt:new Date().toISOString()};this.#tasks.set(t.id,u);return u;}
  delete(id){this.findById(id);this.#tasks.delete(Number(id));}
}

let pass=0,fail=0;
function test(desc,fn){try{fn();console.log("  ✓",desc);pass++;}catch(e){console.log("  ✗",desc,"—",e.message);fail++;}}

const s = new TaskStore();
const t1 = s.create({title:"Buy milk",priority:"low"});
const t2 = s.create({title:"Write tests",priority:"high"});

test("create assigns id",         () => { if(t1.id!==1) throw new Error(t1.id); });
test("findAll returns both",      () => { if(s.findAll().length!==2) throw new Error(); });
test("findById returns task",     () => { if(s.findById(1).title!=="Buy milk") throw new Error(); });
test("findById 404 throws",       () => { try{s.findById(99);throw new Error("no throw");}catch(e){if(!e.status)throw new Error("no status");} });
test("filter by priority",        () => { if(s.findAll({priority:"high"}).length!==1) throw new Error(); });
test("update changes field",      () => { s.update(1,{completed:true}); if(!s.findById(1).completed) throw new Error(); });
test("filter completed=true",     () => { if(s.findAll({completed:"true"}).length!==1) throw new Error(); });
test("delete removes task",       () => { s.delete(2); if(s.findAll().length!==1) throw new Error(); });
test("delete missing throws 404", () => { try{s.delete(99);throw new Error("no throw");}catch(e){if(!e.status)throw new Error(); } });
test("empty title throws 400",    () => { try{s.create({title:""});throw new Error("no throw");}catch(e){if(e.status!==400)throw e;} });

console.log(\`
\${pass} passed, \${fail} failed\`);

node api.mjs          # start the server
node api.test.mjs     # test the store logic (no server needed)