feat(app): undo deleting a card

Deleting a card, from the list or while studying, asks first ("Delete
flashcard?"), then offers Undo for a few seconds ("Flashcard deleted").
Meanwhile the card leaves every list and session; once the time to
undo is over, its revisions are blanked and it is deleted for good, as
notes and studysets already are (CardDeletions, a DelayedDeletions).
Undo while studying puts the card back into the round where it was.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/test/core/dependencies/person_scope_test.dart

@@ -6,6 +6,7 @@ import 'package:halkyon_learn_flutter/src/core/dependencies/person_dependencies.
 import 'package:halkyon_learn_flutter/src/core/dependencies/person_scope.dart';
 import 'package:halkyon_learn_flutter/src/core/sync/sync_service.dart';
 import 'package:halkyon_learn_flutter/src/feature/auth/model/auth_status.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/learning_path/data/learning_path_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/learning_path/data/learning_path_repository.dart';
@@ -62,6 +63,7 @@ PersonDependencies personDependencies({Future<void> Function()? onDispose}) {
     assets: assets,
     deletions: StudysetDeletions(studysets, cards, notes, paths, pdfSources),
     noteDeletions: NoteDeletions(notes),
+    cardDeletions: CardDeletions(cards),
     pathDeletions: LearningPathDeletions(paths),
     stepDeletions: StepDeletions(paths),
     pdfDeletions: PdfDeletions(pdfSources),

halkyon_learn_flutter/test/feature/card/bloc/card_blocs_test.dart

@@ -1,6 +1,7 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:halkyon_learn_flutter/src/core/content/rich_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/bloc/card_list_bloc.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/study/data/review_repository.dart';
@@ -22,14 +23,17 @@ void main() {
   late CardRepository cards;
   late TagRepository tags;
   late ReviewRepository reviews;
+  late CardDeletions deletions;
 
   setUp(() {
     gateway = FakeCardGateway();
     cards = CardRepository(gateway);
     tags = TagRepository(FakeTagGateway(), cardChanges: cards.changes);
     reviews = ReviewRepository(FakeReviewGateway());
+    deletions = CardDeletions(cards, undoWindow: Duration.zero);
   });
   tearDown(() async {
+    await deletions.dispose();
     await reviews.dispose();
     await tags.dispose();
     await cards.dispose();
@@ -40,7 +44,7 @@ void main() {
       'a card reported or buried shows so, and either is taken back',
       () async {
         final id = await cards.create('japanese', card('猫', 'cat'));
-        final bloc = CardListBloc(cards, tags, reviews, 'japanese')
+        final bloc = CardListBloc(cards, tags, reviews, deletions, 'japanese')
           ..add(const CardListEventStarted());
         addTearDown(bloc.close);
         Future<CardListStateLoaded> next(
@@ -70,7 +74,7 @@ void main() {
 
     test('lists the cards and follows every change', () async {
       await cards.create('japanese', card('猫', 'cat'));
-      final bloc = CardListBloc(cards, tags, reviews, 'japanese')
+      final bloc = CardListBloc(cards, tags, reviews, deletions, 'japanese')
         ..add(const CardListEventStarted());
       addTearDown(bloc.close);
 
@@ -100,7 +104,7 @@ void main() {
     test('moves a card', () async {
       await cards.create('japanese', card('a', ''));
       await cards.create('japanese', card('b', ''));
-      final bloc = CardListBloc(cards, tags, reviews, 'japanese')
+      final bloc = CardListBloc(cards, tags, reviews, deletions, 'japanese')
         ..add(const CardListEventStarted());
       addTearDown(bloc.close);
       final loaded = await bloc.stream.firstWhere(
@@ -137,7 +141,7 @@ void main() {
       await tags.setTagsOf(ids[0], {noun});
       await tags.setTagsOf(ids[1], {noun});
       await tags.setTagsOf(ids[2], {verb});
-      bloc = CardListBloc(cards, tags, reviews, 'japanese')
+      bloc = CardListBloc(cards, tags, reviews, deletions, 'japanese')
         ..add(const CardListEventStarted());
     });
     tearDown(() => bloc.close());

halkyon_learn_flutter/test/feature/card/widget/card_widgets_test.dart

@@ -110,10 +110,8 @@ void main() {
     expect(find.text('Changed on two devices'), findsOneWidget);
   });
 
-  testWidgets("a card's options delete it, after asking", (tester) async {
-    final id = await cards.create('japanese', card('猫', 'cat'));
-    await showList(tester);
-
+  /// Deletes the card shown through its options, saying yes.
+  Future<void> delete(WidgetTester tester) async {
     await tester.tap(
       find.descendant(
         of: find.byType(CardTile),
@@ -126,11 +124,38 @@ void main() {
     await tester.pump();
     await tester.pump();
     await tester.pumpAndSettle();
+    expect(find.text('Delete flashcard?'), findsOneWidget);
     await tester.tap(find.widgetWithText(FilledButton, 'Delete'));
     await tester.pumpAndSettle();
+  }
 
-    expect(gateway.deletions, ['blank $id', 'delete $id']);
+  testWidgets("a card's options delete it, after asking; once the time to "
+      'undo is over, for good', (tester) async {
+    final id = await cards.create('japanese', card('猫', 'cat'));
+    await showList(tester);
+
+    await delete(tester);
+
+    expect(find.text('Flashcard deleted'), findsOneWidget);
     expect(find.text('No flashcards yet'), findsOneWidget);
+    expect(gateway.deletions, isEmpty);
+    await tester.pump(const Duration(seconds: 5));
+    await tester.pumpAndSettle();
+    expect(gateway.deletions, ['blank $id', 'delete $id']);
+  });
+
+  testWidgets('Undo keeps a card deleted a moment ago', (tester) async {
+    await cards.create('japanese', card('猫', 'cat'));
+    await showList(tester);
+
+    await delete(tester);
+    await tester.tap(find.text('Undo'));
+    await tester.pumpAndSettle();
+    await tester.pump(const Duration(seconds: 5));
+    await tester.pumpAndSettle();
+
+    expect(find.text('猫'), findsOneWidget);
+    expect(gateway.deletions, isEmpty);
   });
 
   testWidgets("a card's options report it and bury it, each shown on the "

halkyon_learn_flutter/test/feature/study/bloc/study_session_bloc_test.dart

@@ -3,6 +3,7 @@ import 'dart:math' as math;
 import 'package:clock/clock.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:halkyon_learn_flutter/src/core/content/rich_content.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/settings/data/settings_repository.dart';
@@ -35,6 +36,7 @@ void main() {
   late FakeStudysetGateway studysetGateway;
   late StudysetRepository studysets;
   late CardRepository cards;
+  late CardDeletions deletions;
   late FakeReviewGateway reviewGateway;
   late ReviewRepository reviews;
   late TagRepository tags;
@@ -49,6 +51,7 @@ void main() {
       );
     studysets = StudysetRepository(studysetGateway);
     cards = CardRepository(FakeCardGateway());
+    deletions = CardDeletions(cards, undoWindow: Duration.zero);
     reviewGateway = FakeReviewGateway();
     reviews = ReviewRepository(reviewGateway);
     tags = TagRepository(FakeTagGateway());
@@ -56,6 +59,7 @@ void main() {
     now = DateTime.utc(2026, 10, 5, 9);
   });
   tearDown(() async {
+    await deletions.dispose();
     await studysets.dispose();
     await cards.dispose();
     await tags.dispose();
@@ -66,6 +70,7 @@ void main() {
   StudySessionBloc session() => StudySessionBloc(
     studysets,
     cards,
+    deletions,
     reviews,
     tags,
     settings,
@@ -188,6 +193,8 @@ void main() {
         bloc.add(const StudySessionEventCardDeleted());
         expect((await showing(bloc, '犬')).pills, hasLength(1));
       });
+      // Deleted for good once the time to undo it is over.
+      await Future<void>.delayed(const Duration(milliseconds: 50));
 
       expect(
         (await cards.cardsOf('japanese')).map((each) => each.content.front),
@@ -794,6 +801,7 @@ void main() {
     StudySessionBloc focused(StudyFocus focus) => StudySessionBloc(
       studysets,
       cards,
+      deletions,
       reviews,
       tags,
       settings,

halkyon_learn_flutter/test/feature/study/widget/study_screen_test.dart

@@ -253,7 +253,11 @@ void main() {
     await tester.tap(find.widgetWithText(FilledButton, 'Delete'));
     await tester.pumpAndSettle();
 
+    expect(find.text('Flashcard deleted'), findsOneWidget);
     expect(find.textContaining('犬', findRichText: true), findsOneWidget);
+    // For good once the time to undo it is over.
+    await tester.pump(const Duration(seconds: 5));
+    await tester.pumpAndSettle();
     expect(await cards.cardsOf('japanese'), hasLength(1));
   });
 

halkyon_learn_flutter/test/support/test_dependencies.dart

@@ -20,6 +20,7 @@ import 'package:halkyon_learn_flutter/src/feature/anki/data/anki_package.dart';
 import 'package:halkyon_learn_flutter/src/feature/anki/data/anki_package_reader.dart';
 import 'package:halkyon_learn_flutter/src/feature/auth/data/auth_gateway.dart';
 import 'package:halkyon_learn_flutter/src/feature/auth/data/auth_repository.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_gateway.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/geo_map/data/geo_map_repository.dart';
@@ -170,6 +171,7 @@ Dependencies testDependencies({
           pdfSources,
         );
         final noteDeletions = NoteDeletions(notes);
+        final cardDeletions = CardDeletions(cards);
         final pathDeletions = LearningPathDeletions(paths);
         final stepDeletions = StepDeletions(paths);
         final pdfDeletions = PdfDeletions(pdfSources);
@@ -187,6 +189,7 @@ Dependencies testDependencies({
           assets: assets,
           deletions: deletions,
           noteDeletions: noteDeletions,
+          cardDeletions: cardDeletions,
           pathDeletions: pathDeletions,
           stepDeletions: stepDeletions,
           pdfDeletions: pdfDeletions,
@@ -194,6 +197,7 @@ Dependencies testDependencies({
           onDispose: () async {
             await deletions.dispose();
             await noteDeletions.dispose();
+            await cardDeletions.dispose();
             await pathDeletions.dispose();
             await stepDeletions.dispose();
             await pdfDeletions.dispose();