action_sheet: Add "Mark Topic As Read" button

Adds button to mark all messages in a topic as read. The button:
- Appears only when the topic has unread messages
- Uses mark_topic_as_read API for server feature level < 155
- Uses messages/flags/narrow API for server feature level >= 155
- Shows error dialog if the request fails

fixes: #1225

assets/l10n/app_en.arb

@@ -716,5 +716,13 @@
   "emojiPickerSearchEmoji": "Search emoji",
   "@emojiPickerSearchEmoji": {
     "description": "Hint text for the emoji picker search text field."
+  },
+  "actionSheetOptionMarkTopicAsRead": "Mark Topic As Read",
+  "@actionSheetOptionMarkTopicAsRead": {
+    "description": "Option to mark a specific topic as read in the action sheet."
+  },
+  "errorMarkTopicAsReadFailed": "Failed to mark the topic as read. Please try again.",
+  "@errorMarkTopicAsReadFailed": {
+    "description": "Error message displayed when marking a topic as read fails."
   }
 }

lib/generated/l10n/zulip_localizations.dart

@@ -1070,6 +1070,18 @@ abstract class ZulipLocalizations {
   /// In en, this message translates to:
   /// **'Search emoji'**
   String get emojiPickerSearchEmoji;
+
+  /// Option to mark a specific topic as read in the action sheet.
+  ///
+  /// In en, this message translates to:
+  /// **'Mark Topic As Read'**
+  String get actionSheetOptionMarkTopicAsRead;
+
+  /// Error message displayed when marking a topic as read fails.
+  ///
+  /// In en, this message translates to:
+  /// **'Failed to mark the topic as read. Please try again.'**
+  String get errorMarkTopicAsReadFailed;
 }
 
 class _ZulipLocalizationsDelegate extends LocalizationsDelegate<ZulipLocalizations> {

lib/generated/l10n/zulip_localizations_ar.dart

@@ -564,4 +564,10 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
 
   @override
   String get emojiPickerSearchEmoji => 'Search emoji';
+
+  @override
+  String get actionSheetOptionMarkTopicAsRead => 'Mark Topic As Read';
+
+  @override
+  String get errorMarkTopicAsReadFailed => 'Failed to mark the topic as read. Please try again.';
 }

lib/generated/l10n/zulip_localizations_en.dart

@@ -564,4 +564,10 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
 
   @override
   String get emojiPickerSearchEmoji => 'Search emoji';
+
+  @override
+  String get actionSheetOptionMarkTopicAsRead => 'Mark Topic As Read';
+
+  @override
+  String get errorMarkTopicAsReadFailed => 'Failed to mark the topic as read. Please try again.';
 }

lib/generated/l10n/zulip_localizations_ja.dart

@@ -564,4 +564,10 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
 
   @override
   String get emojiPickerSearchEmoji => 'Search emoji';
+
+  @override
+  String get actionSheetOptionMarkTopicAsRead => 'Mark Topic As Read';
+
+  @override
+  String get errorMarkTopicAsReadFailed => 'Failed to mark the topic as read. Please try again.';
 }

lib/generated/l10n/zulip_localizations_nb.dart

@@ -564,4 +564,10 @@ class ZulipLocalizationsNb extends ZulipLocalizations {
 
   @override
   String get emojiPickerSearchEmoji => 'Search emoji';
+
+  @override
+  String get actionSheetOptionMarkTopicAsRead => 'Mark Topic As Read';
+
+  @override
+  String get errorMarkTopicAsReadFailed => 'Failed to mark the topic as read. Please try again.';
 }

lib/generated/l10n/zulip_localizations_pl.dart

@@ -564,4 +564,10 @@ class ZulipLocalizationsPl extends ZulipLocalizations {
 
   @override
   String get emojiPickerSearchEmoji => 'Szukaj emoji';
+
+  @override
+  String get actionSheetOptionMarkTopicAsRead => 'Mark Topic As Read';
+
+  @override
+  String get errorMarkTopicAsReadFailed => 'Failed to mark the topic as read. Please try again.';
 }

lib/generated/l10n/zulip_localizations_ru.dart

@@ -564,4 +564,10 @@ class ZulipLocalizationsRu extends ZulipLocalizations {
 
   @override
   String get emojiPickerSearchEmoji => 'Поиск эмодзи';
+
+  @override
+  String get actionSheetOptionMarkTopicAsRead => 'Mark Topic As Read';
+
+  @override
+  String get errorMarkTopicAsReadFailed => 'Failed to mark the topic as read. Please try again.';
 }

lib/generated/l10n/zulip_localizations_sk.dart

@@ -564,4 +564,10 @@ class ZulipLocalizationsSk extends ZulipLocalizations {
 
   @override
   String get emojiPickerSearchEmoji => 'Hľadať emotikon';
+
+  @override
+  String get actionSheetOptionMarkTopicAsRead => 'Mark Topic As Read';
+
+  @override
+  String get errorMarkTopicAsReadFailed => 'Failed to mark the topic as read. Please try again.';
 }

lib/widgets/action_sheet.dart

@@ -240,6 +240,14 @@ void showTopicActionSheet(BuildContext context, {
       pageContext: context);
   }));
 
+  final unreadCount = store.unreads.countInTopicNarrow(channelId, topic);
+  if (unreadCount > 0) {
+    optionButtons.add(MarkTopicAsReadButton(
+      channelId: channelId,
+      topic: topic,
+      pageContext: context));
+  }
+
   if (optionButtons.isEmpty) {
     // TODO(a11y): This case makes a no-op gesture handler; as a consequence,
     //   we're presenting some UI (to people who use screen-reader software) as
@@ -372,6 +380,31 @@ class UserTopicUpdateButton extends ActionSheetMenuItemButton {
   }
 }
 
+class MarkTopicAsReadButton extends ActionSheetMenuItemButton {
+  const MarkTopicAsReadButton({
+    super.key,
+    required this.channelId,
+    required this.topic,
+    required super.pageContext,
+  });
+
+  final int channelId;
+  final TopicName topic;
+
+  @override IconData get icon => ZulipIcons.message_checked;
+
+  @override
+  String label(ZulipLocalizations zulipLocalizations) {
+    return zulipLocalizations.actionSheetOptionMarkTopicAsRead;
+  }
+
+  @override void onPressed() async {
+    if (!pageContext.mounted) return;
+    final narrow = TopicNarrow(channelId, topic);
+    await markNarrowAsRead(pageContext, narrow);
+  }
+}
+
 /// Show a sheet of actions you can take on a message in the message list.
 ///
 /// Must have a [MessageListPage] ancestor.

test/widgets/action_sheet_test.dart

@@ -1061,6 +1061,82 @@ void main() {
       });
     });
 
+    group('MarkTopicAsReadButton', () {
+      Future<void> setupToTopicActionSheetWithUnreadMessages(WidgetTester tester, {
+        ZulipStream? channel,
+      }) async {
+        addTearDown(testBinding.reset);
+
+        final effectiveChannel = channel ?? eg.stream();
+        const topicName = TopicName('test topic');
+        final message = eg.streamMessage(stream: effectiveChannel, topic: 'test topic');
+        await testBinding.globalStore.add(eg.selfAccount, eg.initialSnapshot(
+          realmUsers: [eg.selfUser],
+          streams: [effectiveChannel],
+          subscriptions: [eg.subscription(effectiveChannel)]));
+        store = await testBinding.globalStore.perAccount(eg.selfAccount.id);
+        connection = store.connection as FakeApiConnection;
+
+        connection.prepare(json: eg.newestGetMessagesResult(
+          foundOldest: true, messages: [message]).toJson());
+
+        await store.addMessage(message);
+        store.unreads.streams[effectiveChannel.streamId] ??= {};
+        store.unreads.streams[effectiveChannel.streamId]![topicName] ??= QueueList<int>();
+        store.unreads.streams[effectiveChannel.streamId]![topicName]!.add(message.id);
+
+        await tester.pumpWidget(TestZulipApp(accountId: eg.selfAccount.id,
+          child: MessageListPage(initNarrow: TopicNarrow(effectiveChannel.streamId, topicName))));
+        await tester.pumpAndSettle();
+
+        await tester.longPress(find.byType(ZulipAppBar));
+        await tester.pump(const Duration(milliseconds: 250));
+      }
+
+      Future<void> setupToTopicActionSheetWithNoUnreadMessages(WidgetTester tester) async {
+        addTearDown(testBinding.reset);
+
+        final channel = eg.stream();
+        const topicName = TopicName('test topic');
+        final message = eg.streamMessage(stream: channel, topic: 'test topic', flags: [MessageFlag.read]);
+
+        await testBinding.globalStore.add(eg.selfAccount, eg.initialSnapshot(
+          realmUsers: [eg.selfUser],
+          streams: [channel],
+          subscriptions: [eg.subscription(channel)]));
+        store = await testBinding.globalStore.perAccount(eg.selfAccount.id);
+        connection = store.connection as FakeApiConnection;
+
+        connection.prepare(json: eg.newestGetMessagesResult(
+          foundOldest: true, messages: [message]).toJson());
+
+        await store.addMessage(message);
+
+        await tester.pumpWidget(TestZulipApp(accountId: eg.selfAccount.id,
+          child: MessageListPage(initNarrow: TopicNarrow(channel.streamId, topicName))));
+        await tester.pumpAndSettle();
+
+        await tester.longPress(find.byType(ZulipAppBar));
+        await tester.pump(const Duration(milliseconds: 250));
+      }
+
+      group('visibility', () {
+        testWidgets('shows button when topic has unread messages', (tester) async {
+          await setupToTopicActionSheetWithUnreadMessages(tester);
+
+          final zulipLocalizations = GlobalLocalizations.zulipLocalizations;
+          check(find.text(zulipLocalizations.actionSheetOptionMarkTopicAsRead)).findsOne();
+        });
+
+        testWidgets('hides button when topic has no unread messages', (tester) async {
+          await setupToTopicActionSheetWithNoUnreadMessages(tester);
+
+          final zulipLocalizations = GlobalLocalizations.zulipLocalizations;
+          check(find.text(zulipLocalizations.actionSheetOptionMarkTopicAsRead)).findsNothing();
+        });
+      });
+    });
+
     group('MessageActionSheetCancelButton', () {
       final zulipLocalizations = GlobalLocalizations.zulipLocalizations;