Created redux middleware to store timers

Signed-off-by: Andreas Fahrecker <AndreasFahrecker@gmail.com>

lib/middleware/store_timers_middleware.dart

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+import 'package:redux/redux.dart';
+import 'package:time_progress_calculator/actions/timer_actions.dart';
+import 'package:time_progress_calculator/models/app_state.dart';
+import 'package:time_progress_calculator/models/timer.dart';
+import 'package:time_progress_calculator/persistence/timer_entity.dart';
+import 'package:time_progress_calculator/persistence/timers_repository.dart';
+import 'package:time_progress_calculator/selectors/timer_selectors.dart';
+
+List<Middleware<AppState>> createStoreTimersMiddleware(
+    TimersRepository repository) {
+  final saveTimers = _createSaveTimers(repository);
+  final loadTimers = _createLoadTimers(repository);
+
+  return [
+    TypedMiddleware<AppState, LoadTimersAction>(loadTimers),
+    TypedMiddleware<AppState, AddTimerAction>(saveTimers),
+    TypedMiddleware<AppState, UpdateTimerAction>(saveTimers),
+    TypedMiddleware<AppState, DeleteTimerAction>(saveTimers),
+  ];
+}
+
+Middleware<AppState> _createSaveTimers(TimersRepository repository) {
+  return (Store<AppState> store, dynamic action, NextDispatcher next) {
+    next(action);
+
+    repository.saveTimers(
+      timersSelector(store.state)
+          .map<TimerEntity>((timer) => timer.toEntity())
+          .toList(growable: false),
+    );
+  };
+}
+
+Middleware<AppState> _createLoadTimers(TimersRepository repository) {
+  return (Store<AppState> store, dynamic action, NextDispatcher next) {
+    repository.loadTimers().then((timers) {
+      store.dispatch(
+        TimersLoadedAction(timers.map<Timer>(Timer.fromEntity).toList()),
+      );
+    }).catchError((_) => store.dispatch(TimersNotLoadedAction()));
+  };
+}