message: Handle message deletion event.

When handling a message deletion event, we just simply remove the
messages from the per account store and wipe them from the message list
view if they are present.

Because message deletion can affect what items are to be seen (date
separator, recipient header, etc.), if the view has any message deleted, a
`_reprocessAll` call is triggered. It would be ideal to just removed the
affected items for better performance.

Fixes #120.

Signed-off-by: Zixuan James Li <[email protected]>

lib/model/message.dart

@@ -175,7 +175,12 @@ class MessageStoreImpl with MessageStore {
   }
 
   void handleDeleteMessageEvent(DeleteMessageEvent event) {
-    // TODO handle DeleteMessageEvent, particularly in MessageListView
+    for (final messageId in event.messageIds) {
+      messages.remove(messageId);
+    }
+    for (final view in _messageListViews) {
+      view.messagesRemoved(event.messageIds);
+    }
   }
 
   void handleUpdateMessageFlagsEvent(UpdateMessageFlagsEvent event) {

lib/model/message_list.dart

@@ -155,6 +155,30 @@ mixin _MessageSequence {
     _processMessage(messages.length - 1);
   }
 
+  /// Removes the given messages, if present.
+  ///
+  /// Returns true if at least one message was present, false otherwise.
+  /// If none of [messageIds] are found, this is a no-op.
+  bool _removeMessagesById(Iterable<int> messageIds) {
+    final messagesToRemoveById = <int>{};
+    final contentToRemove = <ZulipContent>{};
+    for (final messageId in messageIds) {
+      final index = _findMessageWithId(messageId);
+      if (index == -1) continue;
+      messagesToRemoveById.add(messageId);
+      contentToRemove.add(contents[index]);
+    }
+    if (messagesToRemoveById.isEmpty) return false;
+
+    assert(contents.length == messages.length);
+    messages.removeWhere((message) => messagesToRemoveById.contains(message.id));
+    contents.removeWhere((content) => contentToRemove.contains(content));
+    assert(contents.length == messages.length);
+    _reprocessAll();
+
+    return true;
+  }
+
   void _insertAllMessages(int index, Iterable<Message> toInsert) {
     // TODO parse/process messages in smaller batches, to not drop frames.
     //   On a Pixel 5, a batch of 100 messages takes ~15-20ms in _insertAllMessages.
@@ -478,6 +502,12 @@ class MessageListView with ChangeNotifier, _MessageSequence {
     }
   }
 
+  void messagesRemoved(List<int> messageIds) {
+    if (_removeMessagesById(messageIds)) {
+      notifyListeners();
+    }
+  }
+
   /// Called when the app is reassembled during debugging, e.g. for hot reload.
   ///
   /// This will redo from scratch any computations we can, such as parsing

test/example_data.dart

@@ -388,6 +388,21 @@ const _unreadMsgs = unreadMsgs;
 // Events.
 //
 
+DeleteMessageEvent deleteMessageEvent(List<StreamMessage> messages) {
+  assert(messages.isNotEmpty);
+  final streamId = messages.first.streamId;
+  final topic = messages.first.topic;
+  assert(messages.every((m) => m.streamId == streamId));
+  assert(messages.every((m) => m.topic == topic));
+  return DeleteMessageEvent(
+    id: 0,
+    messageIds: messages.map((message) => message.id).toList(),
+    messageType: MessageType.stream,
+    streamId: messages[0].streamId,
+    topic: messages[0].topic,
+  );
+}
+
 UpdateMessageEvent updateMessageEditEvent(
   Message origMessage, {
   int? userId = -1, // null means null; default is [selfUser.userId]

test/model/message_list_test.dart

@@ -271,6 +271,44 @@ void main() {
     checkInvariants(model);
   });
 
+  group('DeleteMessageEvent', () {
+    final stream = eg.stream();
+    final messages = List.generate(30, (i) => eg.streamMessage(stream: stream));
+
+    test('in narrow', () async {
+      await prepare(narrow: StreamNarrow(stream.streamId));
+      await prepareMessages(foundOldest: true, messages: messages);
+
+      check(model).messages.length.equals(30);
+      await store.handleEvent(eg.deleteMessageEvent(messages.sublist(0, 10)));
+      checkNotifiedOnce();
+      check(model).messages.length.equals(20);
+      checkInvariants(model);
+    });
+
+    test('not all in narrow', () async {
+      await prepare(narrow: StreamNarrow(stream.streamId));
+      await prepareMessages(foundOldest: true, messages: messages.sublist(5));
+
+      check(model).messages.length.equals(25);
+      await store.handleEvent(eg.deleteMessageEvent(messages.sublist(0, 10)));
+      checkNotifiedOnce();
+      check(model).messages.length.equals(20);
+      checkInvariants(model);
+    });
+
+    test('not in narrow', () async {
+      await prepare(narrow: StreamNarrow(stream.streamId));
+      await prepareMessages(foundOldest: true, messages: messages.sublist(5));
+
+      check(model).messages.length.equals(25);
+      await store.handleEvent(eg.deleteMessageEvent(messages.sublist(0, 5)));
+      checkNotNotified();
+      check(model).messages.length.equals(25);
+      checkInvariants(model);
+    });
+  });
+
   group('notifyListenersIfMessagePresent', () {
     test('message present', () async {
       await prepare(narrow: const CombinedFeedNarrow());

test/model/message_test.dart

@@ -375,6 +375,39 @@ void main() {
     });
   });
 
+  group('handleDeleteMessageEvent', () {
+    test('delete an unknown message', () async {
+      final message1 = eg.streamMessage();
+      final message2 = eg.streamMessage();
+      await prepare();
+      await prepareMessages([message1]);
+      await store.handleEvent(eg.deleteMessageEvent([message2]));
+      checkNotNotified();
+      check(store).messages.values.single.id.equals(message1.id);
+    });
+
+    test('delete messages', () async {
+      final message1 = eg.streamMessage();
+      final message2 = eg.streamMessage();
+      await prepare();
+      await prepareMessages([message1, message2]);
+      await store.handleEvent(eg.deleteMessageEvent([message1, message2]));
+      checkNotifiedOnce();
+      check(store).messages.isEmpty();
+    });
+
+    test('delete an unknown message with a known message', () async {
+      final message1 = eg.streamMessage();
+      final message2 = eg.streamMessage();
+      final message3 = eg.streamMessage();
+      await prepare();
+      await prepareMessages([message1, message2]);
+      await store.handleEvent(eg.deleteMessageEvent([message2, message3]));
+      checkNotifiedOnce();
+      check(store).messages.values.single.id.equals(message1.id);
+    });
+  });
+
   group('handleReactionEvent', () {
     test('add reaction', () async {
       final originalMessage = eg.streamMessage(reactions: []);