Integrate logging system into Flutter app with service registration and testing setup

finlog_app/fluttery/lib/fluttery.dart

@@ -1,5 +1,61 @@
-/// A Calculator.
-class Calculator {
-  /// Returns [value] plus 1.
-  int addOne(int value) => value + 1;
+library;
+
+import 'package:fluttery/logger/logger.dart';
+import 'package:fluttery/src/logger/logger_impl.dart';
+import 'package:kiwi/kiwi.dart';
+
+/// A class to manage services.
+class App {
+  static final _AppService _appService = _AppService();
+
+  /// Registers a service with a factory function to instantiate the implementation.
+  ///
+  /// This ensures that the implementation is created when the service is requested.
+  ///
+  /// `implFactory` - A factory method to create the service implementation.
+  static void registerService<T extends Service>(T Function() implFactory) {
+    _appService.registerSingleton<T>(implFactory);
+  }
+
+  /// Retrieves the registered service.
+  ///
+  /// Returns an instance of the registered service.
+  static T service<T extends Service>() {
+    return _appService.resolve<T>();
+  }
+
+  /// Registers the default services required by the application.
+  static void registerDefaultServices() {
+    registerService<Logger>(() => LoggerImpl());
+  }
+}
+
+/// Abstract class to represent a service.
+abstract class Service {}
+
+/// Internal class to manage the registration and resolution of services.
+class _AppService {
+  static _AppService? _singleton;
+
+  static final KiwiContainer _kiwi = KiwiContainer();
+
+  /// Factory constructor to ensure singleton instance of _AppService.
+  factory _AppService() => _singleton ??= _AppService._();
+
+  /// Private constructor.
+  _AppService._();
+
+  /// Registers a singleton service with a factory function to create the instance.
+  ///
+  /// `serviceFactory` - A factory method to create the service implementation.
+  void registerSingleton<T extends Service>(T Function() serviceFactory) {
+    _kiwi.registerFactory<T>((c) => serviceFactory());
+  }
+
+  /// Resolves and retrieves the registered service.
+  ///
+  /// Returns an instance of the registered service.
+  T resolve<T extends Service>() {
+    return _kiwi.resolve<T>();
+  }
 }