/**
 * Minimal, dependency-free ZIP writer (#plugins, M6+). Produces a stored-metadata
 * + deflate ZIP whose central directory matches exactly what the TREK installer's
 * reader (server safe-extract.ts) parses: EOCD -> central headers -> local headers.
 * Kept tiny and in-tree so the SDK stays dependency-free and the artifact format
 * can never drift from the reader.
 */
import zlib from 'node:zlib';

export interface ZipInput {
  /** Archive-relative path, forward slashes (e.g. "server/index.js"). */
  name: string;
  data: Buffer;
}

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

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

/** List the entry names of a ZIP by walking its central directory (reader for `preflight`). */
export function listZipNames(buf: Buffer): string[] {
  // Find the End-Of-Central-Directory record (scan back from the end past any comment).
  let eocd = -1;
  for (let i = buf.length - 22; i >= 0 && i >= buf.length - 22 - 0xffff; i--) {
    if (buf.readUInt32LE(i) === 0x06054b50) { eocd = i; break; }
  }
  if (eocd < 0) throw new Error('not a ZIP archive (no EOCD record)');
  const count = buf.readUInt16LE(eocd + 10);
  let p = buf.readUInt32LE(eocd + 16); // central directory offset
  const names: string[] = [];
  for (let i = 0; i < count; i++) {
    if (buf.readUInt32LE(p) !== 0x02014b50) throw new Error('corrupt central directory');
    const nameLen = buf.readUInt16LE(p + 28);
    const extraLen = buf.readUInt16LE(p + 30);
    const commentLen = buf.readUInt16LE(p + 32);
    names.push(buf.toString('utf8', p + 46, p + 46 + nameLen));
    p += 46 + nameLen + extraLen + commentLen;
  }
  return names;
}

/** Build a ZIP buffer from a flat list of file entries (no directory entries). */
export function makeZip(files: ZipInput[]): Buffer {
  const local: Buffer[] = [];
  const central: Buffer[] = [];
  let offset = 0;

  for (const f of files) {
    const nameBuf = Buffer.from(f.name.replaceAll(/\\/g, '/'), 'utf8');
    const crc = crc32(f.data);
    // Deflate; fall back to stored if that somehow grows the data.
    const deflated = zlib.deflateRawSync(f.data, { level: 9 });
    const useStore = deflated.length >= f.data.length;
    const method = useStore ? 0 : 8;
    const body = useStore ? f.data : deflated;

    const lfh = Buffer.alloc(30);
    lfh.writeUInt32LE(0x04034b50, 0); // local file header signature
    lfh.writeUInt16LE(20, 4); // version needed
    lfh.writeUInt16LE(0, 6); // flags
    lfh.writeUInt16LE(method, 8);
    lfh.writeUInt16LE(0, 10); // mod time
    lfh.writeUInt16LE(0x21, 12); // mod date (fixed, 1980-01-01)
    lfh.writeUInt32LE(crc, 14);
    lfh.writeUInt32LE(body.length, 18); // compressed size
    lfh.writeUInt32LE(f.data.length, 22); // uncompressed size
    lfh.writeUInt16LE(nameBuf.length, 26);
    lfh.writeUInt16LE(0, 28); // extra length
    local.push(lfh, nameBuf, body);

    const cdh = Buffer.alloc(46);
    cdh.writeUInt32LE(0x02014b50, 0); // central header signature
    cdh.writeUInt16LE(20, 4); // version made by
    cdh.writeUInt16LE(20, 6); // version needed
    cdh.writeUInt16LE(0, 8); // flags
    cdh.writeUInt16LE(method, 10);
    cdh.writeUInt16LE(0, 12); // mod time
    cdh.writeUInt16LE(0x21, 14); // mod date
    cdh.writeUInt32LE(crc, 16);
    cdh.writeUInt32LE(body.length, 20);
    cdh.writeUInt32LE(f.data.length, 24);
    cdh.writeUInt16LE(nameBuf.length, 28);
    cdh.writeUInt16LE(0, 30); // extra length
    cdh.writeUInt16LE(0, 32); // comment length
    cdh.writeUInt16LE(0, 34); // disk number
    cdh.writeUInt16LE(0, 36); // internal attributes
    cdh.writeUInt32LE(0, 38); // external attributes (0 = regular file, never symlink)
    cdh.writeUInt32LE(offset, 42); // local header offset
    central.push(cdh, nameBuf);

    offset += lfh.length + nameBuf.length + body.length;
  }

  const centralBuf = Buffer.concat(central);
  const eocd = Buffer.alloc(22);
  eocd.writeUInt32LE(0x06054b50, 0); // EOCD signature
  eocd.writeUInt16LE(0, 4); // this disk
  eocd.writeUInt16LE(0, 6); // central dir start disk
  eocd.writeUInt16LE(files.length, 8); // entries on this disk
  eocd.writeUInt16LE(files.length, 10); // total entries
  eocd.writeUInt32LE(centralBuf.length, 12); // central dir size
  eocd.writeUInt32LE(offset, 16); // central dir offset
  eocd.writeUInt16LE(0, 20); // comment length

  return Buffer.concat([...local, centralBuf, eocd]);
}