Keep topics data up-to-date by handling events

assets/l10n/app_en.arb

@@ -84,6 +84,10 @@
   "@actionSheetOptionMarkChannelAsRead": {
     "description": "Label for marking a channel as read."
   },
+  "actionSheetOptionTopicList": "Topic list",
+  "@actionSheetOptionTopicList": {
+    "description": "Label for navigating to a channel's topic-list page."
+  },
   "actionSheetOptionMuteTopic": "Mute topic",
   "@actionSheetOptionMuteTopic":  {
     "description": "Label for muting a topic on action sheet."
@@ -713,6 +717,10 @@
   "@mainMenuMyProfile": {
     "description": "Label for main-menu button leading to the user's own profile."
   },
+  "topicsButtonLabel": "TOPICS",
+  "@topicsButtonLabel": {
+    "description": "Label for message list button leading to topic-list page. (Use ALL CAPS for cased alphabets: Latin, Greek, Cyrillic, etc.)"
+  },
   "channelFeedButtonTooltip": "Channel feed",
   "@channelFeedButtonTooltip": {
     "description": "Tooltip for button to navigate to a given channel's feed"

lib/generated/l10n/zulip_localizations.dart

@@ -236,6 +236,12 @@ abstract class ZulipLocalizations {
   /// **'Mark channel as read'**
   String get actionSheetOptionMarkChannelAsRead;
 
+  /// Label for navigating to a channel's topic-list page.
+  ///
+  /// In en, this message translates to:
+  /// **'Topic list'**
+  String get actionSheetOptionTopicList;
+
   /// Label for muting a topic on action sheet.
   ///
   /// In en, this message translates to:
@@ -1064,6 +1070,12 @@ abstract class ZulipLocalizations {
   /// **'My profile'**
   String get mainMenuMyProfile;
 
+  /// Label for message list button leading to topic-list page. (Use ALL CAPS for cased alphabets: Latin, Greek, Cyrillic, etc.)
+  ///
+  /// In en, this message translates to:
+  /// **'TOPICS'**
+  String get topicsButtonLabel;
+
   /// Tooltip for button to navigate to a given channel's feed
   ///
   /// In en, this message translates to:

lib/generated/l10n/zulip_localizations_ar.dart

@@ -76,6 +76,9 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
   @override
   String get actionSheetOptionMarkChannelAsRead => 'Mark channel as read';
 
+  @override
+  String get actionSheetOptionTopicList => 'Topic list';
+
   @override
   String get actionSheetOptionMuteTopic => 'Mute topic';
 
@@ -584,6 +587,9 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
   @override
   String get mainMenuMyProfile => 'My profile';
 
+  @override
+  String get topicsButtonLabel => 'TOPICS';
+
   @override
   String get channelFeedButtonTooltip => 'Channel feed';
 

lib/generated/l10n/zulip_localizations_en.dart

@@ -76,6 +76,9 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
   @override
   String get actionSheetOptionMarkChannelAsRead => 'Mark channel as read';
 
+  @override
+  String get actionSheetOptionTopicList => 'Topic list';
+
   @override
   String get actionSheetOptionMuteTopic => 'Mute topic';
 
@@ -584,6 +587,9 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
   @override
   String get mainMenuMyProfile => 'My profile';
 
+  @override
+  String get topicsButtonLabel => 'TOPICS';
+
   @override
   String get channelFeedButtonTooltip => 'Channel feed';
 

lib/generated/l10n/zulip_localizations_ja.dart

@@ -76,6 +76,9 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
   @override
   String get actionSheetOptionMarkChannelAsRead => 'Mark channel as read';
 
+  @override
+  String get actionSheetOptionTopicList => 'Topic list';
+
   @override
   String get actionSheetOptionMuteTopic => 'Mute topic';
 
@@ -584,6 +587,9 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
   @override
   String get mainMenuMyProfile => 'My profile';
 
+  @override
+  String get topicsButtonLabel => 'TOPICS';
+
   @override
   String get channelFeedButtonTooltip => 'Channel feed';
 

lib/generated/l10n/zulip_localizations_nb.dart

@@ -76,6 +76,9 @@ class ZulipLocalizationsNb extends ZulipLocalizations {
   @override
   String get actionSheetOptionMarkChannelAsRead => 'Mark channel as read';
 
+  @override
+  String get actionSheetOptionTopicList => 'Topic list';
+
   @override
   String get actionSheetOptionMuteTopic => 'Mute topic';
 
@@ -584,6 +587,9 @@ class ZulipLocalizationsNb extends ZulipLocalizations {
   @override
   String get mainMenuMyProfile => 'My profile';
 
+  @override
+  String get topicsButtonLabel => 'TOPICS';
+
   @override
   String get channelFeedButtonTooltip => 'Channel feed';
 

lib/generated/l10n/zulip_localizations_pl.dart

@@ -78,6 +78,9 @@ class ZulipLocalizationsPl extends ZulipLocalizations {
   String get actionSheetOptionMarkChannelAsRead =>
       'Oznacz kanał jako przeczytany';
 
+  @override
+  String get actionSheetOptionTopicList => 'Topic list';
+
   @override
   String get actionSheetOptionMuteTopic => 'Wycisz wątek';
 
@@ -593,6 +596,9 @@ class ZulipLocalizationsPl extends ZulipLocalizations {
   @override
   String get mainMenuMyProfile => 'Mój profil';
 
+  @override
+  String get topicsButtonLabel => 'TOPICS';
+
   @override
   String get channelFeedButtonTooltip => 'Strumień kanału';
 

lib/generated/l10n/zulip_localizations_ru.dart

@@ -78,6 +78,9 @@ class ZulipLocalizationsRu extends ZulipLocalizations {
   String get actionSheetOptionMarkChannelAsRead =>
       'Отметить канал как прочитанный';
 
+  @override
+  String get actionSheetOptionTopicList => 'Topic list';
+
   @override
   String get actionSheetOptionMuteTopic => 'Отключить тему';
 
@@ -597,6 +600,9 @@ class ZulipLocalizationsRu extends ZulipLocalizations {
   @override
   String get mainMenuMyProfile => 'Мой профиль';
 
+  @override
+  String get topicsButtonLabel => 'TOPICS';
+
   @override
   String get channelFeedButtonTooltip => 'Лента канала';
 

lib/generated/l10n/zulip_localizations_sk.dart

@@ -76,6 +76,9 @@ class ZulipLocalizationsSk extends ZulipLocalizations {
   @override
   String get actionSheetOptionMarkChannelAsRead => 'Mark channel as read';
 
+  @override
+  String get actionSheetOptionTopicList => 'Topic list';
+
   @override
   String get actionSheetOptionMuteTopic => 'Stlmiť tému';
 
@@ -586,6 +589,9 @@ class ZulipLocalizationsSk extends ZulipLocalizations {
   @override
   String get mainMenuMyProfile => 'Môj profil';
 
+  @override
+  String get topicsButtonLabel => 'TOPICS';
+
   @override
   String get channelFeedButtonTooltip => 'Channel feed';
 

lib/generated/l10n/zulip_localizations_uk.dart

@@ -79,6 +79,9 @@ class ZulipLocalizationsUk extends ZulipLocalizations {
   String get actionSheetOptionMarkChannelAsRead =>
       'Позначити канал як прочитаний';
 
+  @override
+  String get actionSheetOptionTopicList => 'Topic list';
+
   @override
   String get actionSheetOptionMuteTopic => 'Заглушити тему';
 
@@ -596,6 +599,9 @@ class ZulipLocalizationsUk extends ZulipLocalizations {
   @override
   String get mainMenuMyProfile => 'Мій профіль';
 
+  @override
+  String get topicsButtonLabel => 'TOPICS';
+
   @override
   String get channelFeedButtonTooltip => 'Стрічка каналу';
 

lib/model/channel.dart

@@ -1,8 +1,15 @@
+import 'dart:async';
+
+import 'package:collection/collection.dart';
 import 'package:flutter/foundation.dart';
 
 import '../api/model/events.dart';
 import '../api/model/initial_snapshot.dart';
 import '../api/model/model.dart';
+import '../api/route/channels.dart';
+import 'store.dart';
+
+final _apiGetStreamTopics = getStreamTopics;  // similar to _apiSendMessage in lib/model/message.dart
 
 /// The portion of [PerAccountStore] for channels, topics, and stuff about them.
 ///
@@ -34,6 +41,26 @@ mixin ChannelStore {
   /// and [streamsByName].
   Map<int, Subscription> get subscriptions;
 
+  /// Fetch topics in a stream from the server.
+  ///
+  /// The results from the last successful fetch
+  /// can be retrieved with [getStreamTopics].
+  Future<void> fetchTopics(int streamId);
+
+  /// Pairs of the known topics and its latest message ID, in the given stream.
+  ///
+  /// Returns null if the data has never been fetched yet.
+  /// To fetch it from the server, use [fetchTopics].
+  ///
+  /// The result is guaranteed to be sorted by [GetStreamTopicsEntry.maxId], and the
+  /// topics are guaranteed to be distinct.
+  ///
+  /// In some cases, the same maxId affected by message moves can be present in
+  /// multiple [GetStreamTopicsEntry] entries.  For this reason, the caller
+  /// should not rely on [getStreamTopics] to determine which topic the message
+  /// is in.  Instead, refer to [PerAccountStore.messages].
+  List<GetStreamTopicsEntry>? getStreamTopics(int streamId);
+
   /// The visibility policy that the self-user has for the given topic.
   ///
   /// This does not incorporate the user's channel-level policy,
@@ -161,8 +188,11 @@ enum VisibilityEffect {
 /// Generally the only code that should need this class is [PerAccountStore]
 /// itself.  Other code accesses this functionality through [PerAccountStore],
 /// or through the mixin [ChannelStore] which describes its interface.
-class ChannelStoreImpl with ChannelStore {
-  factory ChannelStoreImpl({required InitialSnapshot initialSnapshot}) {
+class ChannelStoreImpl extends PerAccountStoreBase with ChannelStore {
+  factory ChannelStoreImpl({
+    required CorePerAccountStore core,
+    required InitialSnapshot initialSnapshot,
+  }) {
     final subscriptions = Map.fromEntries(initialSnapshot.subscriptions.map(
       (subscription) => MapEntry(subscription.streamId, subscription)));
 
@@ -182,6 +212,7 @@ class ChannelStoreImpl with ChannelStore {
     }
 
     return ChannelStoreImpl._(
+      core: core,
       streams: streams,
       streamsByName: streams.map((_, stream) => MapEntry(stream.name, stream)),
       subscriptions: subscriptions,
@@ -190,6 +221,7 @@ class ChannelStoreImpl with ChannelStore {
   }
 
   ChannelStoreImpl._({
+    required super.core,
     required this.streams,
     required this.streamsByName,
     required this.subscriptions,
@@ -203,6 +235,34 @@ class ChannelStoreImpl with ChannelStore {
   @override
   final Map<int, Subscription> subscriptions;
 
+  /// Maps indexed by stream IDs, of the known latest message IDs in each topic.
+  ///
+  /// For example: `_latestMessageIdsByStreamTopic[stream.id][topic] = maxId`
+  ///
+  /// In some cases, the same message IDs, when affected by message moves, can
+  /// be present for mutliple stream-topic keys.
+  final Map<int, Map<TopicName, int>> _latestMessageIdsByStreamTopic = {};
+
+  @override
+  Future<void> fetchTopics(int streamId) async {
+    final result = await _apiGetStreamTopics(connection, streamId: streamId,
+      allowEmptyTopicName: true);
+    _latestMessageIdsByStreamTopic[streamId] = {
+      for (final GetStreamTopicsEntry(:name, :maxId) in result.topics)
+        name: maxId,
+    };
+  }
+
+  @override
+  List<GetStreamTopicsEntry>? getStreamTopics(int streamId) {
+    final latestMessageIdsInStream = _latestMessageIdsByStreamTopic[streamId];
+    if (latestMessageIdsInStream == null) return null;
+    return [
+      for (final MapEntry(:key, :value) in latestMessageIdsInStream.entries)
+        GetStreamTopicsEntry(maxId: value, name: key),
+    ].sortedBy((value) => -value.maxId);
+  }
+
   @override
   Map<int, Map<TopicName, UserTopicVisibilityPolicy>> get debugTopicVisibility => topicVisibility;
 
@@ -369,4 +429,45 @@ class ChannelStoreImpl with ChannelStore {
       forStream[event.topicName] = visibilityPolicy;
     }
   }
+
+  /// Handle a [MessageEvent], returning whether listeners should be notified.
+  bool handleMessageEvent(MessageEvent event) {
+    if (event.message is! StreamMessage) return false;
+    final StreamMessage(:streamId, :topic) = event.message as StreamMessage;
+
+    final latestMessageIdsByTopic = _latestMessageIdsByStreamTopic[streamId];
+    if (latestMessageIdsByTopic == null) return false;
+    assert(!latestMessageIdsByTopic.containsKey(topic)
+           || latestMessageIdsByTopic[topic]! < event.message.id);
+    latestMessageIdsByTopic[topic] = event.message.id;
+    return true;
+  }
+
+  /// Handle a [UpdateMessageEvent], returning whether listeners should be
+  /// notified.
+  bool handleUpdateMessageEvent(UpdateMessageEvent event) {
+    if (event.moveData == null) return false;
+    final UpdateMessageMoveData(
+      :origStreamId, :origTopic, :newStreamId, :newTopic, :propagateMode,
+    ) = event.moveData!;
+    bool shouldNotify = false;
+
+    final origLatestMessageIdsByTopics = _latestMessageIdsByStreamTopic[origStreamId];
+    if (propagateMode == PropagateMode.changeAll
+        && origLatestMessageIdsByTopics != null) {
+      shouldNotify = origLatestMessageIdsByTopics.remove(origTopic) != null;
+    }
+
+    final newLatestMessageIdsByTopics = _latestMessageIdsByStreamTopic[newStreamId];
+    if (newLatestMessageIdsByTopics != null) {
+      final movedMaxId = event.messageIds.max;
+      if (!newLatestMessageIdsByTopics.containsKey(newTopic)
+          || newLatestMessageIdsByTopics[newTopic]! < movedMaxId) {
+        newLatestMessageIdsByTopics[newTopic] = movedMaxId;
+        shouldNotify = true;
+      }
+    }
+
+    return shouldNotify;
+  }
 }