import { deflateRawSync } from "node:zlib";

type ZipEntry = Readonly<{ bytes: Uint8Array; path: string }>;

function crc32(bytes: Uint8Array): number {
  let crc = 0xffffffff;
  for (const byte of bytes) {
    crc ^= byte;
    for (let bit = 0; bit < 8; bit += 1) {
      crc = (crc >>> 1) ^ ((crc & 1) === 1 ? 0xedb88320 : 0);
    }
  }
  return (crc ^ 0xffffffff) >>> 0;
}

export function createZip(entries: readonly ZipEntry[], compress = false): Uint8Array {
  const localParts: Buffer[] = [];
  const centralParts: Buffer[] = [];
  let localOffset = 0;
  for (const entry of entries) {
    const name = Buffer.from(entry.path, "utf8");
    const source = Buffer.from(entry.bytes);
    const payload = compress ? deflateRawSync(source) : source;
    const method = compress ? 8 : 0;
    const checksum = crc32(source);
    const local = Buffer.alloc(30);
    local.writeUInt32LE(0x04034b50, 0);
    local.writeUInt16LE(20, 4);
    local.writeUInt16LE(method, 8);
    local.writeUInt32LE(checksum, 14);
    local.writeUInt32LE(payload.byteLength, 18);
    local.writeUInt32LE(source.byteLength, 22);
    local.writeUInt16LE(name.byteLength, 26);
    localParts.push(local, name, payload);

    const central = Buffer.alloc(46);
    central.writeUInt32LE(0x02014b50, 0);
    central.writeUInt16LE(20, 4);
    central.writeUInt16LE(20, 6);
    central.writeUInt16LE(method, 10);
    central.writeUInt32LE(checksum, 16);
    central.writeUInt32LE(payload.byteLength, 20);
    central.writeUInt32LE(source.byteLength, 24);
    central.writeUInt16LE(name.byteLength, 28);
    central.writeUInt32LE(localOffset, 42);
    centralParts.push(central, name);
    localOffset += local.byteLength + name.byteLength + payload.byteLength;
  }
  const centralDirectory = Buffer.concat(centralParts);
  const end = Buffer.alloc(22);
  end.writeUInt32LE(0x06054b50, 0);
  end.writeUInt16LE(entries.length, 8);
  end.writeUInt16LE(entries.length, 10);
  end.writeUInt32LE(centralDirectory.byteLength, 12);
  end.writeUInt32LE(localOffset, 16);
  return Buffer.concat([...localParts, centralDirectory, end]);
}