feat(details): implement similar headlines bloc

- Fetches similar headlines
- Filters out current headline
- Handles loading, empty, and error states

Author: fulleni

lib/headline-details/bloc/similar_headlines_bloc.dart

@@ -0,0 +1,64 @@
+import 'dart:async';
+
+import 'package:bloc/bloc.dart';
+import 'package:equatable/equatable.dart';
+import 'package:ht_data_repository/ht_data_repository.dart';
+import 'package:ht_shared/ht_shared.dart' show Headline, HtHttpException;
+
+part 'similar_headlines_event.dart';
+part 'similar_headlines_state.dart';
+
+class SimilarHeadlinesBloc
+    extends Bloc<SimilarHeadlinesEvent, SimilarHeadlinesState> {
+  SimilarHeadlinesBloc({
+    required HtDataRepository<Headline> headlinesRepository,
+  })  : _headlinesRepository = headlinesRepository,
+        super(SimilarHeadlinesInitial()) {
+    on<FetchSimilarHeadlines>(_onFetchSimilarHeadlines);
+  }
+
+  final HtDataRepository<Headline> _headlinesRepository;
+  static const int _similarHeadlinesLimit = 5;
+
+  Future<void> _onFetchSimilarHeadlines(
+    FetchSimilarHeadlines event,
+    Emitter<SimilarHeadlinesState> emit,
+  ) async {
+    emit(SimilarHeadlinesLoading());
+    try {
+      final currentHeadline = event.currentHeadline;
+      if (currentHeadline.category == null ||
+          currentHeadline.category!.id.isEmpty) {
+        emit(SimilarHeadlinesEmpty());
+        return;
+      }
+
+      final queryParams = {
+        'categories': currentHeadline.category!.id,
+      };
+
+      final response = await _headlinesRepository.readAllByQuery(
+        queryParams,
+        limit: _similarHeadlinesLimit + 1, // Fetch one extra to check if current is there
+      );
+
+      // Filter out the current headline from the results
+      final similarHeadlines = response.items
+          .where((headline) => headline.id != currentHeadline.id)
+          .toList();
+
+      // Take only the required limit after filtering
+      final finalSimilarHeadlines = similarHeadlines.take(_similarHeadlinesLimit).toList();
+
+      if (finalSimilarHeadlines.isEmpty) {
+        emit(SimilarHeadlinesEmpty());
+      } else {
+        emit(SimilarHeadlinesLoaded(similarHeadlines: finalSimilarHeadlines));
+      }
+    } on HtHttpException catch (e) {
+      emit(SimilarHeadlinesError(message: e.message));
+    } catch (e) {
+      emit(SimilarHeadlinesError(message: 'An unexpected error occurred: $e'));
+    }
+  }
+}