// Ghi file ZIP không nén (đủ để xuất workspace) — không cần thư viện ngoài.

const CRC_TABLE = (() => {
  const t = new Uint32Array(256);
  for (let n = 0; n < 256; n++) {
    let c = n;
    for (let k = 0; k < 8; k++) c = c & 1 ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
    t[n] = c >>> 0;
  }
  return t;
})();

export function crc32(data: Uint8Array): number {
  let c = 0xffffffff;
  for (let i = 0; i < data.length; i++) c = CRC_TABLE[(c ^ data[i]) & 0xff] ^ (c >>> 8);
  return (c ^ 0xffffffff) >>> 0;
}

/** files: đường dẫn → nội dung văn bản. */
export function makeZip(files: Record<string, string>): Blob {
  const enc = new TextEncoder();
  const parts: Uint8Array[] = [];
  const central: Uint8Array[] = [];
  let offset = 0;
  const now = new Date();
  const time = (now.getHours() << 11) | (now.getMinutes() << 5) | (now.getSeconds() >> 1);
  const date = ((now.getFullYear() - 1980) << 9) | ((now.getMonth() + 1) << 5) | now.getDate();

  for (const [path, text] of Object.entries(files)) {
    const name = enc.encode(path.replace(/^\/+/, ''));
    const data = enc.encode(text);
    const crc = crc32(data);

    const local = new Uint8Array(30 + name.length);
    const lv = new DataView(local.buffer);
    lv.setUint32(0, 0x04034b50, true);
    lv.setUint16(4, 20, true);
    lv.setUint16(6, 0x0800, true);
    lv.setUint16(8, 0, true);
    lv.setUint16(10, time, true);
    lv.setUint16(12, date, true);
    lv.setUint32(14, crc, true);
    lv.setUint32(18, data.length, true);
    lv.setUint32(22, data.length, true);
    lv.setUint16(26, name.length, true);
    local.set(name, 30);

    const cd = new Uint8Array(46 + name.length);
    const cv = new DataView(cd.buffer);
    cv.setUint32(0, 0x02014b50, true);
    cv.setUint16(4, 20, true);
    cv.setUint16(6, 20, true);
    cv.setUint16(8, 0x0800, true);
    cv.setUint16(10, 0, true);
    cv.setUint16(12, time, true);
    cv.setUint16(14, date, true);
    cv.setUint32(16, crc, true);
    cv.setUint32(20, data.length, true);
    cv.setUint32(24, data.length, true);
    cv.setUint16(28, name.length, true);
    cv.setUint32(42, offset, true);
    cd.set(name, 46);

    parts.push(local, data);
    central.push(cd);
    offset += local.length + data.length;
  }

  const cdSize = central.reduce((n, c) => n + c.length, 0);
  const end = new Uint8Array(22);
  const ev = new DataView(end.buffer);
  ev.setUint32(0, 0x06054b50, true);
  ev.setUint16(8, central.length, true);
  ev.setUint16(10, central.length, true);
  ev.setUint32(12, cdSize, true);
  ev.setUint32(16, offset, true);

  return new Blob([...parts, ...central, end] as BlobPart[], { type: 'application/zip' });
}