const http = require("http");
const fs = require("fs");
const path = require("path");

const PORT = process.env.PORT || 3000;
const DATA = path.join(__dirname, "data.json");

function readData() {
  try { return JSON.parse(fs.readFileSync(DATA, "utf8")); } catch (_) { return { tasks: [], schedule: [], reminders: [], settings: { theme: "light", notifications: true } }; }
}
function writeData(data) {
  fs.writeFileSync(DATA, JSON.stringify(data, null, 2));
}
function body(req) {
  return new Promise((resolve) => {
    let s = "";
    req.on("data", (c) => (s += c));
    req.on("end", () => { try { resolve(JSON.parse(s || "{}")); } catch (_) { resolve({}); } });
  });
}

http.createServer(async (req, res) => {
  res.setHeader("Access-Control-Allow-Origin", "*");
  res.setHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
  res.setHeader("Access-Control-Allow-Headers", "Content-Type");
  if (req.method === "OPTIONS") { res.writeHead(200); return res.end(); }

  const url = req.url.split("?")[0];

  // API: задачи
  if (req.method === "GET" && url === "/api/tasks") {
    const data = readData();
    res.writeHead(200, { "Content-Type": "application/json" });
    return res.end(JSON.stringify(data.tasks || []));
  }
  if (req.method === "POST" && url === "/api/tasks") {
    const data = readData();
    const task = await body(req);
    task.id = Date.now();
    task.status = task.status || "pending";
    task.createdAt = new Date().toISOString().slice(0, 10);
    data.tasks.push(task);
    writeData(data);
    res.writeHead(200, { "Content-Type": "application/json" });
    return res.end(JSON.stringify({ ok: true, task }));
  }
  if (req.method === "PUT" && url.startsWith("/api/tasks/")) {
    const id = parseInt(url.split("/").pop());
    const data = readData();
    const idx = data.tasks.findIndex(t => t.id === id);
    if (idx === -1) { res.writeHead(404); return res.end("Not found"); }
    const updates = await body(req);
    data.tasks[idx] = { ...data.tasks[idx], ...updates };
    writeData(data);
    res.writeHead(200, { "Content-Type": "application/json" });
    return res.end(JSON.stringify({ ok: true }));
  }
  if (req.method === "DELETE" && url.startsWith("/api/tasks/")) {
    const id = parseInt(url.split("/").pop());
    const data = readData();
    data.tasks = data.tasks.filter(t => t.id !== id);
    writeData(data);
    res.writeHead(200, { "Content-Type": "application/json" });
    return res.end(JSON.stringify({ ok: true }));
  }

  // API: расписание
  if (req.method === "GET" && url === "/api/schedule") {
    const data = readData();
    res.writeHead(200, { "Content-Type": "application/json" });
    return res.end(JSON.stringify(data.schedule || []));
  }
  if (req.method === "POST" && url === "/api/schedule") {
    const data = readData();
    const item = await body(req);
    item.id = Date.now();
    data.schedule.push(item);
    writeData(data);
    res.writeHead(200, { "Content-Type": "application/json" });
    return res.end(JSON.stringify({ ok: true }));
  }
  if (req.method === "DELETE" && url.startsWith("/api/schedule/")) {
    const id = parseInt(url.split("/").pop());
    const data = readData();
    data.schedule = data.schedule.filter(s => s.id !== id);
    writeData(data);
    res.writeHead(200, { "Content-Type": "application/json" });
    return res.end(JSON.stringify({ ok: true }));
  }

  // API: статистика
  if (req.method === "GET" && url === "/api/stats") {
    const data = readData();
    const tasks = data.tasks || [];
    const now = new Date();
    const today = now.toISOString().slice(0, 10);
    const stats = {
      total: tasks.length,
      completed: tasks.filter(t => t.status === "completed").length,
      pending: tasks.filter(t => t.status === "pending").length,
      overdue: tasks.filter(t => t.status === "overdue" || (t.status === "pending" && t.dueDate < today)).length,
      bySubject: {},
      weekActivity: [0, 0, 0, 0, 0, 0, 0]
    };
    tasks.forEach(t => {
      stats.bySubject[t.subject] = (stats.bySubject[t.subject] || 0) + 1;
      if (t.createdAt) {
        const d = new Date(t.createdAt);
        const dayIdx = d.getDay();
        stats.weekActivity[dayIdx]++;
      }
    });
    res.writeHead(200, { "Content-Type": "application/json" });
    return res.end(JSON.stringify(stats));
  }

  // Статика
  let file = url === "/" ? "/index.html" : url;
  const full = path.join(__dirname, file);
  if (full.startsWith(__dirname) && fs.existsSync(full) && fs.statSync(full).isFile()) {
    const ext = path.extname(full);
    const type = ext === ".css" ? "text/css" : ext === ".js" ? "application/javascript" : "text/html";
    res.writeHead(200, { "Content-Type": type + "; charset=utf-8" });
    return res.end(fs.readFileSync(full));
  }
  res.writeHead(404); res.end("Not found");
}).listen(PORT, () => console.log("Сервер запущен на порту " + PORT));