fix: Notifying the client when we remove a message from a thread

Now, everytime a message has a tmid(is a thread), and it gets deleted, we decrease the replyCount of the parent message
then remove the unread thread unread, to make sure all the subscriptions are up to date (and notify to the client)
At the end, we check if the parent message had all of its thread messages deleted, if so, we notify the change in the parent message itself

apps/meteor/app/lib/server/functions/deleteMessage.ts

@@ -1,14 +1,14 @@
 import { AppEvents, Apps } from '@rocket.chat/apps';
 import { api, Message } from '@rocket.chat/core-services';
-import type { AtLeast, IMessage, IUser } from '@rocket.chat/core-typings';
-import { Messages, Rooms, Uploads, Users, ReadReceipts } from '@rocket.chat/models';
+import type { AtLeast, IMessage, IRoom, IUser } from '@rocket.chat/core-typings';
+import { Messages, Rooms, Uploads, Users, ReadReceipts, Subscriptions } from '@rocket.chat/models';
 import { Meteor } from 'meteor/meteor';
 
 import { callbacks } from '../../../../lib/callbacks';
 import { canDeleteMessageAsync } from '../../../authorization/server/functions/canDeleteMessage';
 import { FileUpload } from '../../../file-upload/server';
 import { settings } from '../../../settings/server';
-import { notifyOnRoomChangedById, notifyOnMessageChange } from '../lib/notifyListener';
+import { notifyOnRoomChangedById, notifyOnMessageChange, notifyOnSubscriptionChangedByRoomIdAndUserId } from '../lib/notifyListener';
 
 export const deleteMessageValidatingPermission = async (message: AtLeast<IMessage, '_id'>, userId: IUser['_id']): Promise<void> => {
 	if (!message?._id) {
@@ -51,7 +51,7 @@ export async function deleteMessage(message: IMessage, user: IUser): Promise<voi
 	}
 
 	if (deletedMsg?.tmid) {
-		await Messages.decreaseReplyCountById(deletedMsg.tmid, -1);
+		await deleteThreadMessage(deletedMsg as Required<Pick<IMessage, 'tmid'>>, user, room);
 	}
 
 	const files = (message.files || [message.file]).filter(Boolean); // Keep compatibility with old messages
@@ -107,3 +107,22 @@ export async function deleteMessage(message: IMessage, user: IUser): Promise<voi
 		void bridges.getListenerBridge().messageEvent(AppEvents.IPostMessageDeleted, deletedMsg, user);
 	}
 }
+
+async function deleteThreadMessage(message: Required<Pick<IMessage, 'tmid'>>, user: IUser, room: IRoom | null): Promise<void> {
+	await Messages.decreaseReplyCountById(message.tmid, -1);
+
+	if (room) {
+		const { modifiedCount } = await Subscriptions.removeUnreadThreadsByRoomId(room._id, [message.tmid]);
+		if (modifiedCount > 0) {
+			void notifyOnSubscriptionChangedByRoomIdAndUserId(room._id, user._id);
+		}
+	}
+
+	// Check if this was the last reply in the thread
+	const thread = await Messages.findOneById(message.tmid, { projection: { tcount: 1 } });
+	if (thread?.tcount === 0) {
+		void notifyOnMessageChange({
+			id: message.tmid,
+		});
+	}
+}