plezy/lib/screens/libraries/library_alpha_bar_strategy.dart

import '../../media/library_first_character.dart';
import '../../media/media_backend.dart';
import '../../services/plex_client.dart';
import 'alpha_jump_helper.dart';

/// Backend-specific alpha-jump-bar behaviour.
///
/// Plex libraries use real per-letter counts from
/// `/library/sections/{id}/firstCharacter`, so the bar is scroll-position
/// driven — tapping a letter scrolls to that letter's cumulative offset and
/// the highlighted letter follows the visible row.
///
/// MediaBrowser libraries have no per-letter count endpoint. The bar
/// synthesises the 27-letter alphabet (`#`, `A`–`Z`) and acts as a name-prefix
/// filter that refetches the page when the user picks a letter (matching the
/// server web clients' UX).
abstract class LibraryAlphaBarStrategy {
  /// Whether the bar should be rendered at all. Implementations consider
  /// total item count, sort key, and current filter state.
  bool shouldShow({
    required int totalItemCount,
    required int loadedCharacterCount,
    required String? sortKey,
    required bool isFolderGrouping,
    required String? mediaBrowserAlphaPrefix,
    required bool isPhone,
  });

  /// Load the first-character buckets for the current filter state.
  /// Returns the new helper plus the synthesised character list — the caller
  /// stores both in widget state.
  Future<({List<LibraryFirstCharacter> chars, AlphaJumpHelper helper})> loadCharacters({
    required Map<String, String> filters,
    required int? typeId,
    required bool descending,
  });

  /// Letter to highlight given the current scroll-derived index. Plex maps
  /// the index back through the cumulative offsets; MediaBrowser backends echo
  /// back whatever filter is active.
  String currentLetter(int index, AlphaJumpHelper helper, {String? mediaBrowserAlphaPrefix});

  /// Handle a tap on the letter at [targetIndex]. Plex strategies invoke
  /// [onPlexJump] with the cumulative item index for in-grid scrolling;
  /// MediaBrowser strategies invoke [onMediaBrowserPrefixChange] with the next
  /// `NameStartsWith` prefix (or `null` to clear the filter when the user
  /// re-taps the active letter). Each strategy ignores the callback that
  /// doesn't apply to its UX, so callers can wire both unconditionally.
  void onLetterPressed(
    int targetIndex,
    AlphaJumpHelper helper, {
    required String? currentMediaBrowserPrefix,
    required void Function(int index) onPlexJump,
    required void Function(String? nextPrefix) onMediaBrowserPrefixChange,
  });

  /// Construct the right strategy for [backend].
  factory LibraryAlphaBarStrategy.forBackend(
    MediaBackend backend, {
    required PlexClient Function() plexClientProvider,
    required String libraryKey,
    required bool isShared,
  }) {
    return switch (backend) {
      MediaBackend.plex => PlexAlphaBarStrategy(
        plexClientProvider: plexClientProvider,
        libraryKey: libraryKey,
        isShared: isShared,
      ),
      MediaBackend.jellyfin || MediaBackend.emby => const MediaBrowserAlphaBarStrategy(),
    };
  }
}

/// Plex strategy — calls `/library/sections/{id}/firstCharacter` for real
/// per-letter counts and uses the cumulative offsets to drive scroll
/// position.
class PlexAlphaBarStrategy implements LibraryAlphaBarStrategy {
  final PlexClient Function() plexClientProvider;
  final String libraryKey;
  final bool isShared;

  PlexAlphaBarStrategy({required this.plexClientProvider, required this.libraryKey, required this.isShared});

  @override
  bool shouldShow({
    required int totalItemCount,
    required int loadedCharacterCount,
    required String? sortKey,
    required bool isFolderGrouping,
    required String? mediaBrowserAlphaPrefix,
    required bool isPhone,
  }) {
    if (isFolderGrouping) return false;
    if (loadedCharacterCount < 6 || totalItemCount < 80) return false;
    final s = sortKey ?? '';
    return s.isEmpty || s.startsWith('titleSort');
  }

  @override
  Future<({List<LibraryFirstCharacter> chars, AlphaJumpHelper helper})> loadCharacters({
    required Map<String, String> filters,
    required int? typeId,
    required bool descending,
  }) async {
    if (isShared) {
      // Shared libraries don't support first-characters.
      return (chars: const <LibraryFirstCharacter>[], helper: AlphaJumpHelper(const []));
    }
    final client = plexClientProvider();
    final params = Map<String, String>.from(filters);
    params['includeCollections'] = '1';
    final chars = await client.getFirstCharacters(libraryKey, type: typeId, filters: params.isNotEmpty ? params : null);
    return (chars: chars, helper: AlphaJumpHelper(chars, descending: descending));
  }

  @override
  String currentLetter(int index, AlphaJumpHelper helper, {String? mediaBrowserAlphaPrefix}) =>
      helper.currentLetter(index);

  /// Plex jumps the grid to the cumulative offset for the tapped letter —
  /// the helper's letter list already encodes the per-letter ranges from
  /// the server's `/firstCharacter` counts.
  @override
  void onLetterPressed(
    int targetIndex,
    AlphaJumpHelper helper, {
    required String? currentMediaBrowserPrefix,
    required void Function(int index) onPlexJump,
    required void Function(String? nextPrefix) onMediaBrowserPrefixChange,
  }) {
    onPlexJump(targetIndex);
  }
}

/// MediaBrowser strategy — synthesises the 27-letter alphabet locally and
/// uses the bar as a `NameStartsWith` filter.
class MediaBrowserAlphaBarStrategy implements LibraryAlphaBarStrategy {
  static const _letters = [
    '#',
    'A',
    'B',
    'C',
    'D',
    'E',
    'F',
    'G',
    'H',
    'I',
    'J',
    'K',
    'L',
    'M',
    'N',
    'O',
    'P',
    'Q',
    'R',
    'S',
    'T',
    'U',
    'V',
    'W',
    'X',
    'Y',
    'Z',
  ];

  const MediaBrowserAlphaBarStrategy();

  @override
  bool shouldShow({
    required int totalItemCount,
    required int loadedCharacterCount,
    required String? sortKey,
    required bool isFolderGrouping,
    required String? mediaBrowserAlphaPrefix,
    required bool isPhone,
  }) {
    if (isPhone) return false;
    if (isFolderGrouping) return false;
    if (loadedCharacterCount == 0) return false;
    return totalItemCount >= 80 || mediaBrowserAlphaPrefix != null;
  }

  @override
  Future<({List<LibraryFirstCharacter> chars, AlphaJumpHelper helper})> loadCharacters({
    required Map<String, String> filters,
    required int? typeId,
    required bool descending,
  }) async {
    final synthetic = [for (final l in _letters) LibraryFirstCharacter(key: l, title: l, size: 1)];
    return (chars: synthetic, helper: AlphaJumpHelper(synthetic, descending: descending));
  }

  @override
  String currentLetter(int index, AlphaJumpHelper helper, {String? mediaBrowserAlphaPrefix}) =>
      mediaBrowserAlphaPrefix ?? '';

  /// MediaBrowser backends reuse the alpha bar as a `NameStartsWith` filter.
  /// We map the bar offset back to a letter (the synthesised `size: 1` entries
  /// make offset == position in [helper.letters]) and toggle the filter —
  /// re-tap the active letter to clear, otherwise set the new prefix.
  @override
  void onLetterPressed(
    int targetIndex,
    AlphaJumpHelper helper, {
    required String? currentMediaBrowserPrefix,
    required void Function(int index) onPlexJump,
    required void Function(String? nextPrefix) onMediaBrowserPrefixChange,
  }) {
    if (targetIndex < 0 || targetIndex >= helper.letters.length) return;
    final letter = helper.letters[targetIndex];
    final next = (currentMediaBrowserPrefix == letter) ? null : letter;
    onMediaBrowserPrefixChange(next);
  }
}