Initial Flutter booru app

lib/backend/services/favorite_service.dart

@@ -0,0 +1,37 @@
+import '../../core/utils/result.dart';
+import '../models/favorite.dart';
+import '../models/post.dart';
+import '../repositories/favorite_repository.dart';
+import '../repositories/post_repository.dart';
+
+class FavoriteService {
+  FavoriteService(this._repository, [this._postRepository]);
+
+  final FavoriteRepository _repository;
+  final PostRepository? _postRepository;
+
+  Future<Result<void>> addFavorite(Post post) => _repository.add(post);
+  Future<Result<void>> removeFavorite(String postId, String providerId) {
+    return _repository.remove(postId, providerId);
+  }
+
+  Future<Result<bool>> isFavorite(String postId, String providerId) {
+    return _repository.exists(postId, providerId);
+  }
+
+  Future<Result<List<Favorite>>> getFavorites() => _repository.all();
+  Future<Result<List<Post>>> getFavoritePosts() async {
+    final postRepository = _postRepository;
+    if (postRepository == null) return const Success([]);
+    final favoritesResult = await _repository.all();
+    if (favoritesResult is Error<List<Favorite>>) {
+      return Error(favoritesResult.failure);
+    }
+    final favorites = (favoritesResult as Success<List<Favorite>>).data;
+    return postRepository.getCachedPostsByKeys(
+      favorites.map((favorite) => '${favorite.providerId}:${favorite.postId}'),
+    );
+  }
+
+  Future<Result<void>> clearFavorites() => _repository.clear();
+}