import argparse
import os
import sys
from pathlib import Path


def _key():
  # Steam radio key.
  return bytes.fromhex("""
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ee635b12158d1bccabf9394c9303bfa7
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  """)


def _xor(buf, off, key):
  # Absolute offset.
  if off < 0:
    raise ValueError('Negative ENQ offset.')
  size = len(key)
  idx = off % size
  out = bytearray(buf)
  for i in range(len(out)):
    out[i] ^= key[idx]
    idx += 1
    # Repeating table.
    if idx == size:
      idx = 0
  return bytes(out)


def decode(enq: Path, mp3: Path) -> int:
    """ENQ to MP3.

    Returns byte count.
    Failed writes can
    leave partial output.
    """
    key = _key()
    off = 0
    # No overwrites.
    # Keep the header.
    # ENQ stays intact.
    with enq.open('rb') as fin, mp3.open('xb') as fout:
      while True:
        buf = fin.read(1024 * 1024)
        if not buf:
          break
        fout.write(_xor(buf, off, key))
        # Next read's offset.
        off += len(buf)
    return off


def decode_tree(folder: Path) -> tuple[int, int, int]:
    """Walk radio folders.

    Returns counts:
    decoded, skipped,
    failed. Links are
    not followed.
    """
    if not folder.is_dir():
        raise NotADirectoryError(str(folder))
    done = skipped = failed = 0
    errors = []
    for base, dirs, files in os.walk(folder, onerror=errors.append):
        base = Path(base)
        # Stay in this tree.
        dirs[:] = [name for name in dirs
                   if not (base / name).is_symlink()
                   and not (base / name).is_junction()]
        for name in sorted(files):
            enq = base / name
            # Not linked audio.
            if enq.suffix.lower() != '.enq' or enq.is_symlink():
                continue
            mp3 = enq.with_suffix('.mp3')
            try:
                size = decode(enq, mp3)
            except FileExistsError:
                # Creation races too.
                skipped += 1
                print('Skipped existing output: %s' % mp3)
            except (OSError, ValueError) as exc:
                # Try the next file.
                failed += 1
                print('Failed: %s: %s' % (enq, exc), file=sys.stderr)
            else:
                done += 1
                print('Recovered %d bytes: %s' % (size, mp3))
    for exc in errors:
        # Include scan errors.
        print('Cannot scan: %s' % exc, file=sys.stderr)
    return done, skipped, failed + len(errors)


def _cli():
  cli = argparse.ArgumentParser(description="Rig'n'Roll ENQ to MP3")
  cli.add_argument('folder', type=Path, help='Folder to search recursively for ENQ files')
  opt = cli.parse_args()
  if not opt.folder.is_dir():
    cli.error('Input must be an existing folder')
  return cli, opt


def main():
  cli, opt = _cli()
  try:
    done, skipped, failed = decode_tree(opt.folder)
  except (OSError, ValueError) as exc:
    cli.error(str(exc))
  print('Decoded: %d; skipped: %d; failed: %d' % (done, skipped, failed))
  return 1 if failed else 0


if __name__ == '__main__':
    sys.exit(main())