feat: delay when the avatar is not detected (#327)

* test: included undectedDelay

* docs: documented change

* refactor: changed material import for meta

* docs: removed comma

* refactor: fixed typo for "undected"

lib/avatar_detector/bloc/avatar_detector_bloc.dart

@@ -4,6 +4,7 @@ import 'package:avatar_detector_repository/avatar_detector_repository.dart';
 import 'package:bloc/bloc.dart';
 import 'package:camera/camera.dart';
 import 'package:equatable/equatable.dart';
+import 'package:meta/meta.dart';
 import 'package:tensorflow_models/tensorflow_models.dart' as tf;
 
 part 'avatar_detector_event.dart';
@@ -18,6 +19,16 @@ class AvatarDetectorBloc
   }
   final AvatarDetectorRepository _avatarDetectorRepository;
 
+  /// The time to wait before considering the [Avatar] as not detected.
+  @visibleForTesting
+  static const undetectedDelay = Duration(seconds: 2);
+
+  /// The last time the [Avatar] was detected.
+  ///
+  /// Initially set to [DateTime.now] after the model is [_initialized]; then
+  /// set to [DateTime.now] after every [Avatar] detection.
+  late DateTime _lastAvatarDetection;
+
   @override
   Future<void> close() {
     _avatarDetectorRepository.dispose();
@@ -37,6 +48,7 @@ class AvatarDetectorBloc
       emit(
         state.copyWith(status: AvatarDetectorStatus.loaded),
       );
+      _lastAvatarDetection = DateTime.now();
     } on Exception catch (error, trace) {
       addError(error, trace);
       emit(
@@ -61,9 +73,11 @@ class AvatarDetectorBloc
     try {
       final avatar = await _avatarDetectorRepository.detectAvatar(imageData);
       if (avatar == null) {
-        emit(
+        if (DateTime.now().difference(_lastAvatarDetection) > undetectedDelay) {
-          state.copyWith(status: AvatarDetectorStatus.notDetected),
+          emit(
-        );
+            state.copyWith(status: AvatarDetectorStatus.notDetected),
+          );
+        }
       } else {
         emit(
           state.copyWith(
@@ -71,6 +85,7 @@ class AvatarDetectorBloc
             avatar: avatar,
           ),
         );
+        _lastAvatarDetection = DateTime.now();
       }
     } catch (error, stackTrace) {
       addError(error, stackTrace);

test/avatar_detector/bloc/avatar_detector_bloc_test.dart

@@ -161,7 +161,46 @@ void main() {
       blocTest<AvatarDetectorBloc, AvatarDetectorState>(
         'emits [AvatarDetectorStatus.loading, AvatarDetectorStatus.loaded, '
         'AvatarDetectorStatus.estimating, AvatarDetectorStatus.notDetected] '
-        'if detectAvatar returns null.',
+        'if detectAvatar returns null and undetectedDelay elapsed.',
+        setUp: () {
+          when(
+            () => avatarDetectorRepository.detectAvatar(any()),
+          ).thenAnswer((_) async => null);
+        },
+        build: () => AvatarDetectorBloc(avatarDetectorRepository),
+        act: (bloc) async {
+          bloc.add(AvatarDetectorInitialized());
+          await Future<void>.delayed(AvatarDetectorBloc.undetectedDelay);
+          bloc.add(AvatarDetectorEstimateRequested(_FakeCameraImage()));
+        },
+        expect: () => [
+          isInstanceOf<AvatarDetectorState>().having(
+            (state) => state.status,
+            'status',
+            equals(AvatarDetectorStatus.loading),
+          ),
+          isInstanceOf<AvatarDetectorState>().having(
+            (state) => state.status,
+            'status',
+            equals(AvatarDetectorStatus.loaded),
+          ),
+          isInstanceOf<AvatarDetectorState>().having(
+            (state) => state.status,
+            'status',
+            equals(AvatarDetectorStatus.estimating),
+          ),
+          isInstanceOf<AvatarDetectorState>().having(
+            (state) => state.status,
+            'status',
+            equals(AvatarDetectorStatus.notDetected),
+          ),
+        ],
+      );
+
+      blocTest<AvatarDetectorBloc, AvatarDetectorState>(
+        'emits [AvatarDetectorStatus.loading, AvatarDetectorStatus.loaded, '
+        'AvatarDetectorStatus.estimating] '
+        'if detectAvatar returns null and undetectedDelay not elapsed.',
         setUp: () {
           when(
             () => avatarDetectorRepository.detectAvatar(any()),
@@ -189,11 +228,6 @@ void main() {
             'status',
             equals(AvatarDetectorStatus.estimating),
           ),
-          isInstanceOf<AvatarDetectorState>().having(
-            (state) => state.status,
-            'status',
-            equals(AvatarDetectorStatus.notDetected),
-          ),
         ],
       );