// Mock server: static UI + local tile backend (proxy -> OSM, disk-cached).
// The UI only ever talks to localhost; swap the upstream for a real
// tileserver-gl later without touching the frontend.
const http = require('http');
const fs = require('fs');
const path = require('path');
const { Readable } = require('stream');

const PORT = 8077;
const ROOT = __dirname;
const CACHE = path.join(__dirname, '.tilecache');
fs.mkdirSync(CACHE, { recursive: true });

const mime = {
  '.html': 'text/html', '.js': 'text/javascript', '.css': 'text/css',
  '.json': 'application/json', '.svg': 'image/svg+xml', '.png': 'image/png',
};

http.createServer((req, res) => {
  const u = new URL(req.url, 'http://x');

  // ---- tile backend -------------------------------------------------
  if (u.pathname.startsWith('/tiles/')) {
    const parts = u.pathname.split('/');
    const [z, x, y] = [parts[2], parts[3], (parts[4] || '').replace(/\.png$/, '')];
    if (!/^\d+$/.test(z) || !/^\d+$/.test(x) || !/^\d+$/.test(y)) { res.writeHead(400); return res.end(); }
    const file = path.join(CACHE, `${z}/${x}`, `${y}.png`);
    const upstream = `https://tile.openstreetmap.org/${z}/${x}/${y}.png`;
    res.setHeader('Access-Control-Allow-Origin', '*');
    res.setHeader('Content-Type', 'image/png');
    res.setHeader('Cache-Control', 'public, max-age=86400');
    if (fs.existsSync(file)) { res.writeHead(200); fs.createReadStream(file).pipe(res); return; }
    fs.mkdirSync(path.dirname(file), { recursive: true });
    const fail = (code) => { if (!res.headersSent) { res.writeHead(code); res.end(); } else res.destroy(); };
    fetch(upstream, { headers: { 'User-Agent': 'mapmock-dev/0.1 (local tile proxy)', 'Referer': `http://localhost:${PORT}/` } })
      .then(r => {
        if (!r.ok) { return fail(r.status); }
        const body = Readable.fromWeb(r.body);
        body.on('error', () => fail(502));
        res.writeHead(200);
        const ws = fs.createWriteStream(file, { flags: 'x' });
        ws.on('error', () => {});
        body.pipe(ws); body.pipe(res);
      })
      .catch(() => fail(502));
    return;
  }

  // ---- static -------------------------------------------------------
  let p = u.pathname === '/' ? '/index.html' : u.pathname;
  const file = path.join(ROOT, p);
  if (!file.startsWith(ROOT)) { res.writeHead(403); return res.end(); }
  fs.readFile(file, (e, d) => {
    if (e) { res.writeHead(404); return res.end('not found'); }
    res.writeHead(200, { 'Content-Type': mime[path.extname(file)] || 'application/octet-stream' });
    res.end(d);
  });
}).listen(PORT, '0.0.0.0', () => console.log(`map mock: http://localhost:${PORT}  (tiles: /tiles/{z}/{x}/{y}.png)`));