type DownloadableFile = {
  name: string;
  url: string;
};

type ZipEntry = {
  name: Uint8Array;
  data: Uint8Array;
  crc: number;
  offset: number;
};

export async function downloadFilesAsZip(files: DownloadableFile[], archiveName: string) {
  if (!files.length) return;
  const usedNames = new Set<string>();
  const entries: ZipEntry[] = [];
  for (let index = 0; index < files.length; index += 1) {
    const file = files[index];
    const response = await fetch(file.url, { credentials: "same-origin" });
    if (!response.ok) throw new Error(`下载第 ${index + 1} 个图层失败`);
    const data = new Uint8Array(await response.arrayBuffer());
    const safeName = uniqueFileName(sanitizeFileName(file.name) || `layer-${index}.png`, usedNames);
    entries.push({ name: new TextEncoder().encode(safeName), data, crc: crc32(data), offset: 0 });
  }
  const blob = zipBlob(entries);
  const href = URL.createObjectURL(blob);
  const anchor = document.createElement("a");
  anchor.href = href;
  anchor.download = sanitizeFileName(archiveName) || "seedream-layers.zip";
  document.body.appendChild(anchor);
  anchor.click();
  anchor.remove();
  window.setTimeout(() => URL.revokeObjectURL(href), 1000);
}

function zipBlob(entries: ZipEntry[]) {
  const localParts: Uint8Array[] = [];
  let offset = 0;
  for (const entry of entries) {
    entry.offset = offset;
    const header = new Uint8Array(30 + entry.name.length);
    const view = new DataView(header.buffer);
    view.setUint32(0, 0x04034b50, true);
    view.setUint16(4, 20, true);
    view.setUint16(6, 0x0800, true);
    view.setUint16(8, 0, true);
    view.setUint32(14, entry.crc, true);
    view.setUint32(18, entry.data.length, true);
    view.setUint32(22, entry.data.length, true);
    view.setUint16(26, entry.name.length, true);
    header.set(entry.name, 30);
    localParts.push(header, entry.data);
    offset += header.length + entry.data.length;
  }

  const centralOffset = offset;
  const centralParts: Uint8Array[] = [];
  for (const entry of entries) {
    const header = new Uint8Array(46 + entry.name.length);
    const view = new DataView(header.buffer);
    view.setUint32(0, 0x02014b50, true);
    view.setUint16(4, 20, true);
    view.setUint16(6, 20, true);
    view.setUint16(8, 0x0800, true);
    view.setUint16(10, 0, true);
    view.setUint32(16, entry.crc, true);
    view.setUint32(20, entry.data.length, true);
    view.setUint32(24, entry.data.length, true);
    view.setUint16(28, entry.name.length, true);
    view.setUint32(42, entry.offset, true);
    header.set(entry.name, 46);
    centralParts.push(header);
    offset += header.length;
  }

  const end = new Uint8Array(22);
  const endView = new DataView(end.buffer);
  endView.setUint32(0, 0x06054b50, true);
  endView.setUint16(8, entries.length, true);
  endView.setUint16(10, entries.length, true);
  endView.setUint32(12, offset - centralOffset, true);
  endView.setUint32(16, centralOffset, true);
  return new Blob([...localParts, ...centralParts, end].map(arrayBufferCopy), { type: "application/zip" });
}

function arrayBufferCopy(value: Uint8Array) {
  const copy = new Uint8Array(value.byteLength);
  copy.set(value);
  return copy.buffer;
}

function sanitizeFileName(value: string) {
  return value.trim().replace(/[\\/:*?"<>|\u0000-\u001f]/g, "-").replace(/^\.+/, "").slice(0, 120);
}

function uniqueFileName(name: string, used: Set<string>) {
  if (!used.has(name)) {
    used.add(name);
    return name;
  }
  const dot = name.lastIndexOf(".");
  const base = dot > 0 ? name.slice(0, dot) : name;
  const extension = dot > 0 ? name.slice(dot) : "";
  let index = 2;
  while (used.has(`${base}-${index}${extension}`)) index += 1;
  const result = `${base}-${index}${extension}`;
  used.add(result);
  return result;
}

const crcTable = Array.from({ length: 256 }, (_, index) => {
  let value = index;
  for (let bit = 0; bit < 8; bit += 1) value = (value & 1) ? 0xedb88320 ^ (value >>> 1) : value >>> 1;
  return value >>> 0;
});

function crc32(data: Uint8Array) {
  let crc = 0xffffffff;
  for (const value of data) crc = crcTable[(crc ^ value) & 0xff] ^ (crc >>> 8);
  return (crc ^ 0xffffffff) >>> 0;
}