// parseZip — разбор ZIP: центральный каталог → записи {name, data, dosMs, isDir}.
// Поддерживаются методы 0 (store) и 8 (deflate). Без внешних библиотек.

import { decodeZipName } from './decode_zip_name.js';
import { inflateRaw } from './inflate_raw.js';
import { dosToMs } from './dos_to_ms.js';

export async function parseZip(buf) {
  const dv = new DataView(buf.buffer, buf.byteOffset, buf.byteLength);
  let eocd = -1;
  for (let i = buf.length - 22; i >= 0; i--) {
    if (dv.getUint32(i, true) === 0x06054b50) { eocd = i; break; }
  }
  if (eocd < 0) throw new Error('Не ZIP');
  const cdSize = dv.getUint32(eocd + 12, true);
  const cdOffset = dv.getUint32(eocd + 16, true);

  const entries = [];
  let pos = cdOffset;
  const cdEnd = cdOffset + cdSize;
  while (pos < cdEnd) {
    if (dv.getUint32(pos, true) !== 0x02014b50) break;
    const flags = dv.getUint16(pos + 8, true);
    const method = dv.getUint16(pos + 10, true);
    const modTime = dv.getUint16(pos + 12, true);
    const modDate = dv.getUint16(pos + 14, true);
    const compSize = dv.getUint32(pos + 20, true);
    const nameLen = dv.getUint16(pos + 28, true);
    const extraLen = dv.getUint16(pos + 30, true);
    const commentLen = dv.getUint16(pos + 32, true);
    const localOffset = dv.getUint32(pos + 42, true);

    const nameBytes = buf.slice(pos + 46, pos + 46 + nameLen);
    const name = decodeZipName(nameBytes, (flags & 0x800) !== 0);

    const lhNameLen = dv.getUint16(localOffset + 26, true);
    const lhExtraLen = dv.getUint16(localOffset + 28, true);
    const dataStart = localOffset + 30 + lhNameLen + lhExtraLen;
    const comp = buf.slice(dataStart, dataStart + compSize);

    let data;
    if (method === 0) data = comp;
    else if (method === 8) data = await inflateRaw(comp);
    else throw new Error('Метод сжатия ' + method + ' не поддерживается');

    entries.push({ name, data, dosMs: dosToMs(modDate, modTime), isDir: name.endsWith('/') });
    pos += 46 + nameLen + extraLen + commentLen;
  }
  return entries;
}