feat: Implement HeadlineDetailsBloc

- Fetches headline by ID
- Handles loading and error states
- Provides headline data

Author: fulleni

lib/headline-details/bloc/headline_details_bloc.dart

@@ -0,0 +1,46 @@
+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, NotFoundException;
+
+part 'headline_details_event.dart';
+part 'headline_details_state.dart';
+
+class HeadlineDetailsBloc
+    extends Bloc<HeadlineDetailsEvent, HeadlineDetailsState> {
+  HeadlineDetailsBloc({required HtDataRepository<Headline> headlinesRepository})
+      : _headlinesRepository = headlinesRepository,
+        super(HeadlineDetailsInitial()) {
+    on<FetchHeadlineById>(_onFetchHeadlineById);
+    on<HeadlineProvided>(_onHeadlineProvided);
+  }
+
+  final HtDataRepository<Headline> _headlinesRepository;
+
+  Future<void> _onFetchHeadlineById(
+    FetchHeadlineById event,
+    Emitter<HeadlineDetailsState> emit,
+  ) async {
+    emit(HeadlineDetailsLoading());
+    try {
+      final headline = await _headlinesRepository.read(id: event.headlineId);
+      emit(HeadlineDetailsLoaded(headline: headline));
+    } on NotFoundException catch (e) {
+      emit(HeadlineDetailsFailure(message: e.message));
+    } on HtHttpException catch (e) {
+      emit(HeadlineDetailsFailure(message: e.message));
+    } catch (e) {
+      emit(HeadlineDetailsFailure(message: 'An unexpected error occurred: $e'));
+    }
+  }
+
+  void _onHeadlineProvided(
+    HeadlineProvided event,
+    Emitter<HeadlineDetailsState> emit,
+  ) {
+    emit(HeadlineDetailsLoaded(headline: event.headline));
+  }
+}

lib/headline-details/bloc/headline_details_event.dart

@@ -0,0 +1,24 @@
+part of 'headline_details_bloc.dart';
+
+abstract class HeadlineDetailsEvent extends Equatable {
+  const HeadlineDetailsEvent();
+
+  @override
+  List<Object> get props => [];
+}
+
+class FetchHeadlineById extends HeadlineDetailsEvent {
+  const FetchHeadlineById(this.headlineId);
+  final String headlineId;
+
+  @override
+  List<Object> get props => [headlineId];
+}
+
+class HeadlineProvided extends HeadlineDetailsEvent {
+  const HeadlineProvided(this.headline);
+  final Headline headline;
+
+  @override
+  List<Object> get props => [headline];
+}

lib/headline-details/bloc/headline_details_state.dart

@@ -0,0 +1,30 @@
+part of 'headline_details_bloc.dart';
+
+abstract class HeadlineDetailsState extends Equatable {
+  const HeadlineDetailsState();
+
+  @override
+  List<Object> get props => [];
+}
+
+class HeadlineDetailsInitial extends HeadlineDetailsState {}
+
+class HeadlineDetailsLoading extends HeadlineDetailsState {}
+
+class HeadlineDetailsLoaded extends HeadlineDetailsState {
+  const HeadlineDetailsLoaded({required this.headline});
+
+  final Headline headline;
+
+  @override
+  List<Object> get props => [headline];
+}
+
+class HeadlineDetailsFailure extends HeadlineDetailsState {
+  const HeadlineDetailsFailure({required this.message});
+
+  final String message;
+
+  @override
+  List<Object> get props => [message];
+}