msglist: Exclude DMs with muted users from applicable narrows

Direct messages of those conversations are excluded where all the
recipients are muted.

Currently the applicable narrows are:
  - CombinedFeedNarrow
  - MentionsNarrow
  - StarredMessagesNarrow

In the future, this will apply to the ReactionsNarrow from the Web app
too, once we have it.

Author: sm-sayedi

lib/model/message.dart

@@ -435,4 +435,10 @@ class MessageStoreImpl extends PerAccountStoreBase with MessageStore {
     // [Poll] is responsible for notifying the affected listeners.
     poll.handleSubmessageEvent(event);
   }
+
+  void handleMutedUsersEvent(MutedUsersEvent event) {
+    for (final view in _messageListViews) {
+      view.handleMutedUsersEvent(event);
+    }
+  }
 }

lib/model/message_list.dart

@@ -12,6 +12,7 @@ import 'channel.dart';
 import 'content.dart';
 import 'narrow.dart';
 import 'store.dart';
+import 'user.dart';
 
 /// The number of messages to fetch in each request.
 const kMessageListFetchBatchSize = 100; // TODO tune
@@ -431,7 +432,10 @@ class MessageListView with ChangeNotifier, _MessageSequence {
         return switch (message.conversation) {
           StreamConversation(:final streamId, :final topic) =>
             store.isTopicVisible(streamId, topic),
-          DmConversation() => true,
+          DmConversation(:final allRecipientIds) => () {
+            return !store.allRecipientsMuted(DmNarrow(
+              allRecipientIds: allRecipientIds, selfUserId: store.selfUserId));
+          }(),
         };
 
       case ChannelNarrow(:final streamId):
@@ -442,8 +446,15 @@ class MessageListView with ChangeNotifier, _MessageSequence {
 
       case TopicNarrow():
       case DmNarrow():
+        return true;
+
       case MentionsNarrow():
+      // case ReactionsNarrow(): // TODO
       case StarredMessagesNarrow():
+        if (message.conversation case DmConversation(:final allRecipientIds)) {
+          return !store.allRecipientsMuted(DmNarrow(
+            allRecipientIds: allRecipientIds, selfUserId: store.selfUserId));
+        }
         return true;
     }
   }
@@ -455,12 +466,13 @@ class MessageListView with ChangeNotifier, _MessageSequence {
     switch (narrow) {
       case CombinedFeedNarrow():
       case ChannelNarrow():
+      case MentionsNarrow():
+      // case ReactionsNarrow(): // TODO
+      case StarredMessagesNarrow():
         return false;
 
       case TopicNarrow():
       case DmNarrow():
-      case MentionsNarrow():
-      case StarredMessagesNarrow():
         return true;
     }
   }
@@ -484,6 +496,22 @@ class MessageListView with ChangeNotifier, _MessageSequence {
     }
   }
 
+  /// Whether this event could affect the result that [_messageVisible]
+  /// would ever have returned for any possible message in this message list.
+  MutenessEffect? _canAffectMuteness(MutedUsersEvent event) {
+    switch(narrow) {
+      case CombinedFeedNarrow():
+      case MentionsNarrow():
+      case StarredMessagesNarrow():
+        return store.willChangeIfRecipientMuted(event);
+
+      case ChannelNarrow():
+      case TopicNarrow():
+      case DmNarrow():
+        return null;
+    }
+  }
+
   /// Fetch messages, starting from scratch.
   Future<void> fetchInitial() async {
     // TODO(#80): fetch from anchor firstUnread, instead of newest
@@ -662,6 +690,33 @@ class MessageListView with ChangeNotifier, _MessageSequence {
     notifyListeners();
   }
 
+  void handleMutedUsersEvent(MutedUsersEvent event) {
+    switch(_canAffectMuteness(event)) {
+      case MutenessEffect.added:
+        if (_removeMessagesWhere((message) =>
+            (message is DmMessage
+             && store.allRecipientsMuted(
+                  DmNarrow.ofMessage(message, selfUserId: store.selfUserId),
+                  mutedUsers: event.mutedUsers,
+                )))) {
+          notifyListeners();
+        }
+
+      case MutenessEffect.removed:
+        // TODO get the newly-unmuted messages from the message store
+        // For now, we simplify the task by just refetching this message list
+        // from scratch.
+        if (fetched) {
+          _reset();
+          notifyListeners();
+          fetchInitial();
+        }
+
+      default:
+        return;
+    }
+  }
+
   /// Update data derived from the content of the given message.
   ///
   /// This does not notify listeners.

lib/model/store.dart

@@ -942,6 +942,8 @@ class PerAccountStore extends PerAccountStoreBase with ChangeNotifier, EmojiStor
 
       case MutedUsersEvent():
         assert(debugLog("server event: muted_users"));
+        _messages.handleMutedUsersEvent(event);
+        // Update _users last, so other handlers can compare to the old value.
         _users.handleMutedUsersEvent(event);
         notifyListeners();
 

lib/model/user.dart

@@ -86,6 +86,25 @@ mixin UserStore on PerAccountStoreBase {
   bool allRecipientsMuted(DmNarrow narrow, {List<MutedUserItem>? mutedUsers}) {
     return !narrow.otherRecipientIds.any((id) => !isUserMuted(id, mutedUsers: mutedUsers));
   }
+
+  /// Whether the given event will change the result of [allRecipientsMuted]
+  /// for its mutedUsers, compared to the current state.
+  MutenessEffect willChangeIfRecipientMuted(MutedUsersEvent event) {
+    assert(mutedUsers.length != event.mutedUsers.length);
+    return mutedUsers.length < event.mutedUsers.length
+      ? MutenessEffect.added
+      : MutenessEffect.removed;
+  }
+}
+
+/// Whether a given [MutedUsersEvent] will affect the results
+/// that [UserStore.allRecipientsMuted] would give for some messages.
+enum MutenessEffect {
+  /// A new user is added to the muted users list.
+  added,
+
+  /// A new user is removed from the muted users list.
+  removed,
 }
 
 /// The implementation of [UserStore] that does the work.