SpotiFLAC-Mobile/lib/utils/artist_utils.dart

final RegExp _artistNameSplitPattern = RegExp(
  r'\s*(?:,|;|&|\bx\b)\s*|\s+\b(?:feat(?:uring)?|ft|with)\.?(?=\s|$)\s*',
  caseSensitive: false,
);

const artistTagModeJoined = 'joined';
const artistTagModeSplitVorbis = 'split_vorbis';
const artistTagModePrimary = 'primary';

const artistTagModes = {
  artistTagModeJoined,
  artistTagModeSplitVorbis,
  artistTagModePrimary,
};

// Same separator set as the Rust tag writer and the Android finalizer, so
// every write path stores the same primary artist. Unlike the display split
// above, a standalone "x" needs spaces on both sides ("Malcolm X" stays).
final RegExp _primaryArtistSeparator = RegExp(
  r'\s*[,;&]\s*|\s+x\s+|\s+(?:feat(?:uring)?|ft|with)\.?(?:\s+|$)',
  caseSensitive: false,
);
final RegExp _metadataKeyPunctuation = RegExp(r'[^A-Z0-9]');

List<String> splitArtistNames(String rawArtists) {
  final raw = rawArtists.trim();
  if (raw.isEmpty) return const [];

  return raw
      .split(_artistNameSplitPattern)
      .map((part) => part.trim())
      .where((part) => part.isNotEmpty)
      .toList(growable: false);
}

String primaryArtistName(String artists, {String? albumArtist}) {
  final preferred = albumArtist?.trim() ?? '';
  final normalizedPreferred = preferred.toLowerCase();
  final useAlbumArtist =
      preferred.isNotEmpty &&
      normalizedPreferred != 'various artists' &&
      normalizedPreferred != 'various' &&
      normalizedPreferred != 'va';
  final source = useAlbumArtist ? preferred : artists.trim();
  final split = splitArtistNames(source);
  if (split.isNotEmpty) return split.first;

  final fallback = splitArtistNames(artists);
  return fallback.isNotEmpty ? fallback.first : artists.trim();
}

bool shouldSplitVorbisArtistTags(String mode) {
  return mode == artistTagModeSplitVorbis;
}

bool isPrimaryArtistTagMode(String mode) =>
    mode.trim().toLowerCase() == artistTagModePrimary;

/// The first credited artist, or the trimmed value when nothing separates it.
String primaryArtistTagValue(String rawArtists) {
  final trimmed = rawArtists.trim();
  for (final part in trimmed.split(_primaryArtistSeparator)) {
    final artist = part.trim();
    if (artist.isNotEmpty) return artist;
  }
  return trimmed;
}

/// Mode for rewriting tags that already exist or that the user typed (editor,
/// lyrics embedding). Primary is meant for provider credits at download and
/// re-enrichment time and would silently discard names here.
String artistTagModeForExistingTags(String mode) =>
    isPrimaryArtistTagMode(mode) ? artistTagModeJoined : mode;

/// Artist tag value written for [mode]. Joined and split modes keep the full
/// credit; Vorbis splitting happens in the writers.
String artistTagValueForMode(String value, String mode) =>
    isPrimaryArtistTagMode(mode) ? primaryArtistTagValue(value) : value;

/// Rewrites artist and album-artist entries of an embed metadata map for
/// [mode], whichever key spelling the caller used (ARTIST, album_artist,
/// "ALBUM ARTIST", albumArtist). Other entries and empty values are kept.
Map<String, String> applyArtistTagModeToMetadata(
  Map<String, String> metadata,
  String mode,
) {
  if (!isPrimaryArtistTagMode(mode)) return metadata;
  return {
    for (final entry in metadata.entries)
      entry.key: switch (entry.key.toUpperCase().replaceAll(
        _metadataKeyPunctuation,
        '',
      )) {
        'ARTIST' || 'ALBUMARTIST' when entry.value.trim().isNotEmpty =>
          primaryArtistTagValue(entry.value),
        _ => entry.value,
      },
  };
}

List<String> splitArtistTagValues(String rawArtists) {
  final seen = <String>{};
  final values = <String>[];
  for (final part in splitArtistNames(rawArtists)) {
    final key = part.toLowerCase();
    if (seen.add(key)) {
      values.add(part);
    }
  }

  if (values.isNotEmpty) {
    return values;
  }

  final trimmed = rawArtists.trim();
  return trimmed.isEmpty ? const [] : <String>[trimmed];
}