/**
 * 极简 ZIP 打包（store 存储，不压缩）。
 *
 * OOXML 容器（xlsx / docx）本质都是 zip 包，这里只实现写文件所需的最小集合：
 * 本地文件头 + 中央目录 + 目录结束记录。不压缩可以省掉 deflate 依赖，
 * 体积对导出场景可以接受，且所有解析器都兼容。
 */

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

const crc32 = (bytes) => {
  let c = 0xffffffff;
  for (let i = 0; i < bytes.length; i += 1) {
    c = CRC_TABLE[(c ^ bytes[i]) & 0xff] ^ (c >>> 8);
  }
  return (c ^ 0xffffffff) >>> 0;
};

const encoder = new TextEncoder();

export const utf8 = (text) => encoder.encode(text);

/**
 * @param {Array<{name: string, data: Uint8Array}>} files
 * @param {string} mimeType
 * @returns {Blob}
 */
export function createZip(files, mimeType) {
  const now = new Date();
  const dosTime =
    (now.getHours() << 11) | (now.getMinutes() << 5) | Math.floor(now.getSeconds() / 2);
  const dosDate =
    ((now.getFullYear() - 1980) << 9) | ((now.getMonth() + 1) << 5) | now.getDate();

  const localParts = [];
  const centralParts = [];
  let offset = 0;

  files.forEach((file) => {
    const nameBytes = utf8(file.name);
    const data = file.data;
    const crc = crc32(data);

    const local = new Uint8Array(30 + nameBytes.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, dosTime, true);
    lv.setUint16(12, dosDate, true);
    lv.setUint32(14, crc, true);
    lv.setUint32(18, data.length, true);
    lv.setUint32(22, data.length, true);
    lv.setUint16(26, nameBytes.length, true);
    lv.setUint16(28, 0, true);
    local.set(nameBytes, 30);

    const central = new Uint8Array(46 + nameBytes.length);
    const cv = new DataView(central.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, dosTime, true);
    cv.setUint16(14, dosDate, true);
    cv.setUint32(16, crc, true);
    cv.setUint32(20, data.length, true);
    cv.setUint32(24, data.length, true);
    cv.setUint16(28, nameBytes.length, true);
    cv.setUint16(30, 0, true);
    cv.setUint16(32, 0, true);
    cv.setUint16(34, 0, true);
    cv.setUint16(36, 0, true);
    cv.setUint32(38, 0, true);
    cv.setUint32(42, offset, true);
    central.set(nameBytes, 46);

    localParts.push(local, data);
    centralParts.push(central);
    offset += local.length + data.length;
  });

  const centralSize = centralParts.reduce((sum, part) => sum + part.length, 0);
  const end = new Uint8Array(22);
  const ev = new DataView(end.buffer);
  ev.setUint32(0, 0x06054b50, true);
  ev.setUint16(4, 0, true);
  ev.setUint16(6, 0, true);
  ev.setUint16(8, files.length, true);
  ev.setUint16(10, files.length, true);
  ev.setUint32(12, centralSize, true);
  ev.setUint32(16, offset, true);
  ev.setUint16(20, 0, true);

  return new Blob([...localParts, ...centralParts, end], { type: mimeType });
}

export default createZip;