Implement in-memory caching for agenda items

lib/core/cache/generic_cache.dart

@@ -0,0 +1,5 @@
+abstract class GenericCache<T> {
+  Future<void> saveItems(List<T> items);
+
+  Future<List<T>?> getCachedItems();
+}

lib/core/cache/in_memory_cache.dart

@@ -0,0 +1,15 @@
+import 'package:devcon_hub/core/cache/generic_cache.dart';
+
+class InMemoryCache<T> implements GenericCache<T> {
+  List<T>? _cache;
+
+  @override
+  Future<void> saveItems(List<T> items) async {
+    _cache = items;
+  }
+
+  @override
+  Future<List<T>?> getCachedItems() async {
+    return _cache;
+  }
+}

lib/features/home/data/repositories/agenda_repository_impl.dart

@@ -1,3 +1,4 @@
+import 'package:devcon_hub/core/cache/generic_cache.dart';
 import 'package:devcon_hub/features/home/data/datasources/agenda_datasource.dart';
 import 'package:devcon_hub/features/home/data/models/agenda_item_response.dart';
 import 'package:devcon_hub/features/home/domain/entities/agenda_item.dart';
@@ -8,14 +9,27 @@ import 'package:devcon_hub/features/home/domain/repositories/agenda_repository.d
 // Maps AgendaResponse to the domain entity AgendaItem using a toEntity() extension or method.
 class AgendaRepositoryImpl implements AgendaRepository {
   final AgendaDataSource _datasource;
+  final GenericCache<AgendaItem> _cache;
 
-  AgendaRepositoryImpl(this._datasource);
+  AgendaRepositoryImpl(this._datasource, this._cache);
 
   @override
   Future<List<AgendaItem>> getAgendaItems() async {
+    final cached = await _cache.getCachedItems();
+    if (cached != null && cached.isNotEmpty) {
+      return cached;
+    }
+
     final items = await _datasource.fetchAgenda();
-    final agendaItems = items.map((item) => item.toEntity()).toList();
+    final agendaItems = _mapAndSort(items);
+
+    await _cache.saveItems(agendaItems);
+
+    return agendaItems;
+  }
 
+  List<AgendaItem> _mapAndSort(List<AgendaItemResponse> responses) {
+    final agendaItems = responses.map((e) => e.toEntity()).toList();
     agendaItems.sort((a, b) => a.startTime!.compareTo(b.startTime!));
     return agendaItems;
   }

lib/features/home/di/di.dart

@@ -1,6 +1,9 @@
 import 'package:cloud_firestore/cloud_firestore.dart';
+import 'package:devcon_hub/core/cache/generic_cache.dart';
+import 'package:devcon_hub/core/cache/in_memory_cache.dart';
 import 'package:devcon_hub/features/home/data/datasources/agenda_datasource.dart';
 import 'package:devcon_hub/features/home/data/repositories/agenda_repository_impl.dart';
+import 'package:devcon_hub/features/home/domain/entities/agenda_item.dart';
 import 'package:devcon_hub/features/home/domain/repositories/agenda_repository.dart';
 import 'package:devcon_hub/features/home/domain/usecases/get_agenda.dart';
 import 'package:get_it/get_it.dart';
@@ -11,8 +14,12 @@ class AgendaInjector {
       ..registerLazySingleton<AgendaDataSource>(
         () => AgendaDataSource(FirebaseFirestore.instance),
       )
+      ..registerLazySingleton<GenericCache<AgendaItem>>(
+        () => InMemoryCache<AgendaItem>(),
+      )
       ..registerLazySingleton<AgendaRepository>(
-        () => AgendaRepositoryImpl(injector<AgendaDataSource>()),
+        () => AgendaRepositoryImpl(
+            injector<AgendaDataSource>(), injector<GenericCache<AgendaItem>>()),
       )
       ..registerLazySingleton(
         () => GetAgendaUseCase(injector<AgendaRepository>()),

test/core/cache/in_memory_cache_test.dart

@@ -0,0 +1,36 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:devcon_hub/core/cache/in_memory_cache.dart';
+
+void main() {
+  group('InMemoryCache', () {
+    late InMemoryCache<String> cache;
+
+    setUp(() {
+      cache = InMemoryCache<String>();
+    });
+
+    test('initially returns null when cache is empty', () async {
+      final result = await cache.getCachedItems();
+      expect(result, isNull);
+    });
+
+    test('saves and retrieves cached items correctly', () async {
+      final items = ['a', 'b', 'c'];
+
+      await cache.saveItems(items);
+      final result = await cache.getCachedItems();
+
+      expect(result, isNotNull);
+      expect(result, equals(items));
+    });
+
+    test('overwrites previous cache when saveItems is called again', () async {
+      await cache.saveItems(['a']);
+      await cache.saveItems(['x', 'y']);
+
+      final result = await cache.getCachedItems();
+
+      expect(result, equals(['x', 'y']));
+    });
+  });
+}

test/features/agenda/data/repositories/agenda_repository_impl_test.dart

@@ -1,3 +1,5 @@
+import 'package:devcon_hub/core/cache/generic_cache.dart';
+import 'package:devcon_hub/core/cache/in_memory_cache.dart';
 import 'package:devcon_hub/features/home/data/datasources/agenda_datasource.dart';
 import 'package:devcon_hub/features/home/data/models/agenda_item_response.dart';
 import 'package:devcon_hub/features/home/data/repositories/agenda_repository_impl.dart';
@@ -10,10 +12,12 @@ class MockAgendaDataSource extends Mock implements AgendaDataSource {}
 void main() {
   late AgendaRepositoryImpl repository;
   late MockAgendaDataSource mockDataSource;
+  late GenericCache<AgendaItem> agendaCache;
 
   setUp(() {
     mockDataSource = MockAgendaDataSource();
-    repository = AgendaRepositoryImpl(mockDataSource);
+    agendaCache = InMemoryCache<AgendaItem>();
+    repository = AgendaRepositoryImpl(mockDataSource, agendaCache);
   });
 
   test('getAgenda returns list of Agenda entities', () async {