mobile-music/lib/library/browse_query.dart

import '../settings/settings_store.dart';
import '../subsonic/models.dart';

/// Session-scoped filter for a browse view: an optional genre and release year.
/// Held in `state/providers.dart` (not persisted) so the app never silently
/// reopens filtered. Sort order *is* persisted (see [AppSettings]).
class BrowseFilter {
  const BrowseFilter({this.genre, this.year});

  /// Case-insensitive genre match, or null for "all genres".
  final String? genre;

  /// Exact release-year match, or null for "all years".
  final int? year;

  bool get isActive => genre != null || year != null;

  int get activeCount => (genre != null ? 1 : 0) + (year != null ? 1 : 0);

  BrowseFilter copyWith({Object? genre = _unset, Object? year = _unset}) =>
      BrowseFilter(
        genre: identical(genre, _unset) ? this.genre : genre as String?,
        year: identical(year, _unset) ? this.year : year as int?,
      );

  static const Object _unset = Object();
}

/// Distinct, display-cased genres from a set of raw genre strings, sorted
/// alphabetically. Dedupes case-insensitively (keeping first-seen casing) so a
/// server that mixes "Rock"/"rock" collapses to one entry.
List<String> distinctGenres(Iterable<String?> raw) {
  final byKey = <String, String>{};
  for (final g in raw) {
    final v = g?.trim();
    if (v == null || v.isEmpty) continue;
    byKey.putIfAbsent(v.toLowerCase(), () => v);
  }
  final out = byKey.values.toList()
    ..sort((a, b) => a.toLowerCase().compareTo(b.toLowerCase()));
  return out;
}

/// Distinct release years present, newest first.
List<int> distinctYears(Iterable<int?> raw) {
  final set = <int>{};
  for (final y in raw) {
    if (y != null && y > 0) set.add(y);
  }
  final out = set.toList()..sort((a, b) => b.compareTo(a));
  return out;
}

bool _genreMatches(String? itemGenre, String? filterGenre) {
  if (filterGenre == null) return true;
  return itemGenre != null &&
      itemGenre.toLowerCase() == filterGenre.toLowerCase();
}

int _byString(String? a, String? b) =>
    (a ?? '').toLowerCase().compareTo((b ?? '').toLowerCase());

/// Compare where a null [a]/[b] always sorts *last*, regardless of [descending].
/// Takes bare [Comparable] so both `int` (`Comparable<num>`) and `DateTime` work.
int _nullsLast(Comparable? a, Comparable? b, {bool descending = false}) {
  if (a == null && b == null) return 0;
  if (a == null) return 1;
  if (b == null) return -1;
  final c = a.compareTo(b);
  return descending ? -c : c;
}

/// Filter then sort albums for the browse grid. Pure — no I/O.
List<Album> applyAlbumQuery(
  List<Album> albums,
  BrowseFilter filter,
  AlbumSort sort,
) {
  final out = albums
      .where((a) => _genreMatches(a.genre, filter.genre))
      .where((a) => filter.year == null || a.year == filter.year)
      .toList();

  switch (sort) {
    case AlbumSort.nameAsc:
      out.sort((a, b) => _byString(a.name, b.name));
    case AlbumSort.artistAsc:
      out.sort((a, b) {
        final c = _byString(a.artist, b.artist);
        return c != 0 ? c : _byString(a.name, b.name);
      });
    case AlbumSort.yearDesc:
      out.sort((a, b) {
        final c = _nullsLast(a.year, b.year, descending: true);
        return c != 0 ? c : _byString(a.name, b.name);
      });
    case AlbumSort.yearAsc:
      out.sort((a, b) {
        final c = _nullsLast(a.year, b.year);
        return c != 0 ? c : _byString(a.name, b.name);
      });
    case AlbumSort.recentlyAdded:
      out.sort((a, b) {
        final c = _nullsLast(a.createdAt, b.createdAt, descending: true);
        return c != 0 ? c : _byString(a.name, b.name);
      });
  }
  return out;
}

/// Filter then sort tracks for the browse list. Pure — no I/O.
List<Song> applyTrackQuery(
  List<Song> songs,
  BrowseFilter filter,
  TrackSort sort,
) {
  final out = songs
      .where((s) => _genreMatches(s.genre, filter.genre))
      .where((s) => filter.year == null || s.year == filter.year)
      .toList();

  switch (sort) {
    case TrackSort.titleAsc:
      out.sort((a, b) => _byString(a.title, b.title));
    case TrackSort.artistAsc:
      out.sort((a, b) {
        final c = _byString(a.artist, b.artist);
        return c != 0 ? c : _byString(a.title, b.title);
      });
    case TrackSort.albumAsc:
      out.sort((a, b) {
        final c = _byString(a.album, b.album);
        if (c != 0) return c;
        final t = _nullsLast(a.track, b.track);
        return t != 0 ? t : _byString(a.title, b.title);
      });
    case TrackSort.yearDesc:
      out.sort((a, b) {
        final c = _nullsLast(a.year, b.year, descending: true);
        return c != 0 ? c : _byString(a.title, b.title);
      });
    case TrackSort.recentlyAdded:
      out.sort((a, b) {
        final c = _nullsLast(a.createdAt, b.createdAt, descending: true);
        return c != 0 ? c : _byString(a.title, b.title);
      });
  }
  return out;
}