import 'dart:io';

/// Liest ID3-Tags (v1 + v2) und eingebettetes Cover aus MP3-Dateien
class Id3Reader {
  /// Gibt Metadaten zurück: titel, kuenstler, album, coverBytes
  static Map<String, dynamic> lesen(String filepath) {
    final result = <String, dynamic>{
      'titel': '',
      'kuenstler': '',
      'album': '',
      'cover': null,
    };

    try {
      final file = File(filepath);
      if (!file.existsSync()) return result;

      final bytes = file.readAsBytesSync();
      // ID3v1 (letzte 128 Bytes)
      if (bytes.length > 128) {
        final tag = bytes.sublist(bytes.length - 128);
        if (String.fromCharCodes(tag.sublist(0, 3)) == 'TAG') {
          result['titel'] = _trimNull(tag.sublist(3, 33)).trim();
          result['kuenstler'] = _trimNull(tag.sublist(33, 63)).trim();
          result['album'] = _trimNull(tag.sublist(63, 93)).trim();
        }
      }

      // ID3v2 Header (Anfang der Datei) für Cover
      if (bytes.length > 10 && String.fromCharCodes(bytes.sublist(0, 3)) == 'ID3') {
        final size = _synchSafeInt(bytes, 6);
        var pos = 10;
        // Frame-Header lesen
        while (pos < size && pos + 10 < bytes.length) {
          final frameId = String.fromCharCodes(bytes.sublist(pos, pos + 4));
          final frameSize = _frameSize(bytes, pos + 4);
          pos += 10;
          if (frameId == 'APIC' && pos + frameSize <= bytes.length) {
            // APIC = Attached Picture
            var p = pos;
            // Encoding (1 Byte) + MIME-Type
            final enc = bytes[p]; p += 1;
            var mimeEnd = p;
            while (mimeEnd < bytes.length && bytes[mimeEnd] != 0) mimeEnd++;
            final mime = String.fromCharCodes(bytes.sublist(p, mimeEnd));
            p = mimeEnd + 1;
            // Picture Type (1 Byte)
            p += 1;
            // Description (null-terminated)
            var descEnd = p;
            while (descEnd < bytes.length) {
              if (enc == 1 || enc == 2) {
                if (descEnd + 1 < bytes.length && bytes[descEnd] == 0 && bytes[descEnd + 1] == 0) break;
                descEnd += 2;
              } else {
                if (bytes[descEnd] == 0) break;
                descEnd += 1;
              }
            }
            p = descEnd + (enc == 1 || enc == 2 ? 2 : 1);
            final remaining = pos + frameSize - p;
            if (remaining > 0 && p + remaining <= bytes.length) {
              result['cover'] = bytes.sublist(p, p + remaining);
            }
            break;
          }
          pos += frameSize;
        }
      }
    } catch (_) {}

    // Fallback: Dateiname als Titel
    if (result['titel'].isEmpty) {
      result['titel'] = filepath.split('/').last.replaceAll('.mp3', '').replaceAll('.m4a', '');
    }
    return result;
  }

  static String _trimNull(List<int> bytes) {
    final end = bytes.indexWhere((b) => b == 0);
    return String.fromCharCodes(end < 0 ? bytes : bytes.sublist(0, end));
  }

  static int _synchSafeInt(List<int> bytes, int offset) {
    return (bytes[offset] << 21) | (bytes[offset + 1] << 14) | (bytes[offset + 2] << 7) | bytes[offset + 3];
  }

  static int _frameSize(List<int> bytes, int offset) {
    return (bytes[offset] << 24) | (bytes[offset + 1] << 16) | (bytes[offset + 2] << 8) | bytes[offset + 3];
  }
}