import { deflateRawSync } from 'zlib';

const CRC_TABLE = (() => {
  const table = 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);
    table[n] = c >>> 0;
  }
  return table;
})();

function crc32(buffer) {
  let crc = 0xffffffff;
  for (const byte of buffer) crc = CRC_TABLE[(crc ^ byte) & 0xff] ^ (crc >>> 8);
  return (crc ^ 0xffffffff) >>> 0;
}

function dosDateTime(date = new Date()) {
  const year = Math.max(1980, date.getFullYear());
  const time = (date.getHours() << 11) | (date.getMinutes() << 5) | Math.floor(date.getSeconds() / 2);
  const day = date.getDate();
  const month = date.getMonth() + 1;
  const dosDate = ((year - 1980) << 9) | (month << 5) | day;
  return { time, date: dosDate };
}

export function createZip(files) {
  const localParts = [];
  const centralParts = [];
  let offset = 0;
  const stamp = dosDateTime();

  for (const file of files) {
    const name = Buffer.from(String(file.name || 'file.bin').replace(/\\/g, '/'), 'utf8');
    const data = Buffer.isBuffer(file.data) ? file.data : Buffer.from(file.data || '');
    const compressed = deflateRawSync(data, { level: 6 });
    const crc = crc32(data);

    const local = Buffer.alloc(30);
    local.writeUInt32LE(0x04034b50, 0);
    local.writeUInt16LE(20, 4);
    local.writeUInt16LE(0x0800, 6);
    local.writeUInt16LE(8, 8);
    local.writeUInt16LE(stamp.time, 10);
    local.writeUInt16LE(stamp.date, 12);
    local.writeUInt32LE(crc, 14);
    local.writeUInt32LE(compressed.length, 18);
    local.writeUInt32LE(data.length, 22);
    local.writeUInt16LE(name.length, 26);
    local.writeUInt16LE(0, 28);
    localParts.push(local, name, compressed);

    const central = Buffer.alloc(46);
    central.writeUInt32LE(0x02014b50, 0);
    central.writeUInt16LE(20, 4);
    central.writeUInt16LE(20, 6);
    central.writeUInt16LE(0x0800, 8);
    central.writeUInt16LE(8, 10);
    central.writeUInt16LE(stamp.time, 12);
    central.writeUInt16LE(stamp.date, 14);
    central.writeUInt32LE(crc, 16);
    central.writeUInt32LE(compressed.length, 20);
    central.writeUInt32LE(data.length, 24);
    central.writeUInt16LE(name.length, 28);
    central.writeUInt16LE(0, 30);
    central.writeUInt16LE(0, 32);
    central.writeUInt16LE(0, 34);
    central.writeUInt16LE(0, 36);
    central.writeUInt32LE(0, 38);
    central.writeUInt32LE(offset, 42);
    centralParts.push(central, name);

    offset += local.length + name.length + compressed.length;
  }

  const centralDirectory = Buffer.concat(centralParts);
  const end = Buffer.alloc(22);
  end.writeUInt32LE(0x06054b50, 0);
  end.writeUInt16LE(0, 4);
  end.writeUInt16LE(0, 6);
  end.writeUInt16LE(files.length, 8);
  end.writeUInt16LE(files.length, 10);
  end.writeUInt32LE(centralDirectory.length, 12);
  end.writeUInt32LE(offset, 16);
  end.writeUInt16LE(0, 20);

  return Buffer.concat([...localParts, centralDirectory, end]);
}