feat: add riverpod based favorite album provider

lib/provider/spotify/album/favorite.dart

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+part of '../spotify.dart';
+
+class FavoriteAlbumState extends PaginatedState<AlbumSimple> {
+  FavoriteAlbumState({
+    required super.items,
+    required super.offset,
+    required super.limit,
+  });
+
+  @override
+  FavoriteAlbumState copyWith({
+    items,
+    offset,
+    limit,
+  }) {
+    return FavoriteAlbumState(
+      items: items ?? this.items,
+      offset: offset ?? this.offset,
+      limit: limit ?? this.limit,
+    );
+  }
+}
+
+class FavoriteAlbumNotifier
+    extends PaginatedAsyncNotifier<AlbumSimple, FavoriteAlbumState>
+    with SpotifyMixin<FavoriteAlbumState> {
+  @override
+  Future<List<AlbumSimple>> fetch(int offset, int limit) {
+    return spotify.me
+        .savedAlbums()
+        .getPage(limit, offset)
+        .then((value) => value.items?.toList() ?? []);
+  }
+
+  @override
+  build() async {
+    ref.watch(spotifyProvider);
+    return FavoriteAlbumState(
+      items: await fetch(0, 20),
+      offset: 0,
+      limit: 20,
+    );
+  }
+
+  Future<void> saveAlbums(List<String> ids) async {
+    if (state.value == null) return;
+
+    await spotify.me.saveAlbums(ids);
+
+    state = await AsyncValue.guard(() async {
+      final albums = await spotify.albums.list(ids);
+
+      return state.value!.copyWith(
+        items: [
+          ...state.value!.items,
+          ...albums,
+        ],
+      );
+    });
+  }
+}

lib/provider/spotify/spotify.dart

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+library spotify;
+
+import 'package:spotify/spotify.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:spotube/provider/spotify_provider.dart';
+
+part 'album/favorite.dart';
+part 'utils/mixin.dart';
+part 'utils/state.dart';
+part 'utils/provider.dart';

lib/provider/spotify/utils/mixin.dart

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+part of '../spotify.dart';
+
+mixin SpotifyMixin<T> on AsyncNotifier<T> {
+  SpotifyApi get spotify => ref.read(spotifyProvider);
+}

lib/provider/spotify/utils/provider.dart

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+part of '../spotify.dart';
+
+abstract class PaginatedAsyncNotifier<K, T extends PaginatedState<K>>
+    extends AsyncNotifier<T> {
+  Future<List<K>> fetch(int offset, int limit);
+
+  Future<void> fetchMore() async {
+    if (state.value == null || !state.value!.hasMore) return;
+
+    await update(
+      (state) async {
+        final items = await fetch(state.offset + state.limit, state.limit);
+        return state.copyWith(
+          items: [
+            ...state.items,
+            ...items,
+          ],
+          offset: state.offset + state.limit,
+        ) as T;
+      },
+    );
+  }
+}

lib/provider/spotify/utils/state.dart

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+part of '../spotify.dart';
+
+abstract class PaginatedState<K> {
+  final List<K> items;
+  final int offset;
+  final int limit;
+  final bool hasMore;
+
+  PaginatedState({
+    required this.items,
+    required this.offset,
+    required this.limit,
+  }) : hasMore = items.length >= limit;
+
+  PaginatedState<K> copyWith({List<K>? items, int? offset, int? limit});
+}