encode method

List<int> encode(MetadataV1Body data)

Implementation

List<int> encode(MetadataV1Body data) {
  int start = bytes.length - 128;

  final codec = ByteCodec();
  List<int> output = List.from(bytes);

  // exist ID3v1 tags
  if (start >= 0 && codec.decode(output.sublist(start, start + 3)) == 'TAG') {
    start += 3;
  } else {
    start = bytes.length;
    final append = List.filled(128, 0x00);
    output.addAll(append);
    final idBytes = codec.encode('TAG', limitByteLength: 3);
    output.replaceRange(start, start + 3, idBytes);
    start += 3;
  }

  // Title
  if (data.title != null) {
    List<int> titleBytes = codec.encode(data.title!, limitByteLength: 30);
    output.replaceRange(start, start + 30, titleBytes);
  }
  start += 30;

  // Artist
  if (data.artist != null) {
    List<int> artistBytes = codec.encode(data.artist!, limitByteLength: 30);
    output.replaceRange(start, start + 30, artistBytes);
  }
  start += 30;

  // Album
  if (data.album != null) {
    List<int> albumBytes = codec.encode(data.album!, limitByteLength: 30);
    output.replaceRange(start, start + 30, albumBytes);
  }
  start += 30;

  // Year
  if (data.year != null) {
    List<int> yearBytes = codec.encode(data.year!, limitByteLength: 4);
    output.replaceRange(start, start + 4, yearBytes);
  }
  start += 4;

  // Track
  if (data.track != null) {
    assert(data.track! <= 255 && data.track! >= 0);

    if (data.comment != null) {
      List<int> commentBytes =
          codec.encode(data.comment!, limitByteLength: 28);
      output.replaceRange(start, start + 28, commentBytes);
    }
    start += 28;

    // Reverse
    output.replaceRange(start, start + 1, [0x01]);
    start += 1;

    List<int> trackBytes = [data.track!];
    output.replaceRange(start, start + 1, trackBytes);
    start += 1;
  } else {
    // Comment
    if (data.comment != null) {
      List<int> commentBytes =
          codec.encode(data.comment!, limitByteLength: 30);
      output.replaceRange(start, start + 30, commentBytes);
    }
    start += 30;
  }

  // Genre
  if (data.genre != null) {
    assert(data.genre! <= 125 && data.genre! >= 0);
    List<int> genreBytes = [data.genre!];
    output.replaceRange(start, start + 1, genreBytes);
  }
  start += 1;
  return output;
}