import { StringType } from 'token-types';
import { type ITokenizer } from 'strtok3';

export async function isTarHeaderChecksumMatches(tokenizer: ITokenizer): Promise<boolean> {
  const blockSize = 512;
  const typeflagOffset = 156;
  let blockIndex = 0;

  while (true) {
    const header = new Uint8Array(blockSize);
    const size = await tokenizer.peekBuffer(header, { mayBeLess: true });

    console.debug(`Reading block at index ${blockIndex}, bytes read: ${size}`);

    if (size < blockSize) {
      console.debug('Less than 512 bytes read — exiting.');
      break;
    }

    if (header.every(byte => byte === 0)) {
      console.debug('Encountered empty block — assuming end of archive.');
      break;
    }

    const typeflag = String.fromCharCode(header[typeflagOffset]);
    console.debug(`typeflag: "${typeflag}"`);

    const rawSumStr = new StringType(8, 'ascii').get(header, 148);
    const cleanedSumStr = rawSumStr.replace(/\0.*$/, '').trim();

    if (cleanedSumStr === '') {
      console.debug('Checksum field empty or spaces — skipping block.');
      await tokenizer.ignore(blockSize);
      blockIndex++;
      continue;
    }

    const readSum = Number.parseInt(cleanedSumStr, 8);

    console.debug(`Raw checksum string: "${rawSumStr}", cleaned: "${cleanedSumStr}", parsed: ${readSum}`);

    if (Number.isNaN(readSum)) {
      console.debug('Checksum is NaN — skipping block.');
      await tokenizer.ignore(blockSize);
      blockIndex++;
      continue;
    }

    let sum = 0;
    for (let i = 0; i < blockSize; i++) {
      sum += (i >= 148 && i < 156) ? 0x20 : header[i];
    }

    console.debug(`Calculated checksum: ${sum}`);

    if (readSum === sum) {
      console.debug('Checksum valid.');
      if (typeflag !== 'g' && typeflag !== 'x') {
        return true;  // Found valid regular header
      } else {
        console.debug(`Skipping extended header of type "${typeflag}".`);
      }
    } else {
      console.debug('Checksum mismatch — skipping block.');
    }

    await tokenizer.ignore(blockSize);
    blockIndex++;
  }

  return false;
}