// A store-only ZIP writer (spec 002 §2): covers are JPEG/PNG/WebP and don't shrink, so no compression.

export interface ZipEntry {
  name: string;
  bytes: Uint8Array;
  modified: Date;
}

export class ZipError extends Error {
  override name = "ZipError";
}

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;
})();

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

/** MS-DOS time and date, from the UTC fields (ZIP has no time zone). */
function dosTime(d: Date): { time: number; date: number } {
  return {
    time: (d.getUTCHours() << 11) | (d.getUTCMinutes() << 5) | (d.getUTCSeconds() >> 1),
    date: ((Math.max(d.getUTCFullYear(), 1980) - 1980) << 9) | ((d.getUTCMonth() + 1) << 5) | d.getUTCDate(),
  };
}

const UTF8_NAMES = 0x0800;
const LIMIT = 0xffffffff;

export function zipStore(entries: readonly ZipEntry[]): Uint8Array {
  const names = entries.map((e) => new TextEncoder().encode(e.name));
  const local = entries.reduce((sum, e, i) => sum + 30 + names[i]!.length + e.bytes.length, 0);
  const central = names.reduce((sum, n) => sum + 46 + n.length, 0);
  if (local + central + 22 > LIMIT) throw new ZipError("These covers add up to more than 4 GiB; select fewer.");

  const out = new Uint8Array(local + central + 22);
  const view = new DataView(out.buffer);
  const offsets: number[] = [];
  const crcs: number[] = [];
  let at = 0;
  entries.forEach((e, i) => {
    const name = names[i]!;
    const { time, date } = dosTime(e.modified);
    const crc = crc32(e.bytes);
    offsets.push(at);
    crcs.push(crc);
    view.setUint32(at, 0x04034b50, true);
    view.setUint16(at + 4, 20, true);
    view.setUint16(at + 6, UTF8_NAMES, true);
    view.setUint16(at + 8, 0, true);
    view.setUint16(at + 10, time, true);
    view.setUint16(at + 12, date, true);
    view.setUint32(at + 14, crc, true);
    view.setUint32(at + 18, e.bytes.length, true);
    view.setUint32(at + 22, e.bytes.length, true);
    view.setUint16(at + 26, name.length, true);
    view.setUint16(at + 28, 0, true);
    out.set(name, at + 30);
    out.set(e.bytes, at + 30 + name.length);
    at += 30 + name.length + e.bytes.length;
  });
  const centralStart = at;
  entries.forEach((e, i) => {
    const name = names[i]!;
    const { time, date } = dosTime(e.modified);
    view.setUint32(at, 0x02014b50, true);
    view.setUint16(at + 4, 20, true);
    view.setUint16(at + 6, 20, true);
    view.setUint16(at + 8, UTF8_NAMES, true);
    view.setUint16(at + 10, 0, true);
    view.setUint16(at + 12, time, true);
    view.setUint16(at + 14, date, true);
    view.setUint32(at + 16, crcs[i]!, true);
    view.setUint32(at + 20, e.bytes.length, true);
    view.setUint32(at + 24, e.bytes.length, true);
    view.setUint16(at + 28, name.length, true);
    // extra, comment, disk number, internal attributes: 0
    view.setUint32(at + 38, 0, true);
    view.setUint32(at + 42, offsets[i]!, true);
    out.set(name, at + 46);
    at += 46 + name.length;
  });
  view.setUint32(at, 0x06054b50, true);
  view.setUint16(at + 8, entries.length, true);
  view.setUint16(at + 10, entries.length, true);
  view.setUint32(at + 12, at - centralStart, true);
  view.setUint32(at + 16, centralStart, true);
  return out;
}