Instantly mark as read visible new reactions.

Telegram/SourceFiles/data/data_changes.h

@@ -32,7 +32,7 @@ inline constexpr int CountBit(Flag Last = Flag::LastUsedBit) {
 		++i;
 		Assert(i != 64);
 	}
-	return (i + 1);
+	return i;
 }
 
 } // namespace details
@@ -151,8 +151,9 @@ struct MessageUpdate {
 		BotCallbackSent    = (1U << 6),
 		NewMaybeAdded      = (1U << 7),
 		RepliesUnreadCount = (1U << 8),
+		NewUnreadReaction  = (1U << 9),
 
-		LastUsedBit        = (1U << 8),
+		LastUsedBit        = (1U << 9),
 	};
 	using Flags = base::flags<Flag>;
 	friend inline constexpr auto is_flag_type(Flag) { return true; }
@@ -271,9 +272,11 @@ private:
 		void sendNotifications();
 
 	private:
-		static constexpr auto kCount = details::CountBit<Flag>();
+		static constexpr auto kCount = details::CountBit<Flag>() + 1;
 
-		void sendRealtimeNotifications(not_null<DataType*> data, Flags flags);
+		void sendRealtimeNotifications(
+			not_null<DataType*> data,
+			Flags flags);
 
 		std::array<rpl::event_stream<UpdateType>, kCount> _realtimeStreams;
 		base::flat_map<not_null<DataType*>, Flags> _updates;

Telegram/SourceFiles/history/history_item.cpp

@@ -852,8 +852,9 @@ void HistoryItem::updateReactions(const MTPMessageReactions *reactions) {
 	setReactions(reactions);
 	const auto hasUnread = hasUnreadReaction();
 	if (hasUnread && !hadUnread) {
+		// This may read the reaction already.
 		addToUnreadThings(HistoryUnreadThings::AddType::New);
-		if (toContact) {
+		if (toContact && hasUnreadReaction()) {
 			const auto notification = ItemNotification{
 				this,
 				ItemNotificationType::Reaction,

Telegram/SourceFiles/history/history_message.cpp

@@ -1543,9 +1543,16 @@ void HistoryMessage::addToUnreadThings(HistoryUnreadThings::AddType type) {
 	}
 	if (hasUnreadReaction()) {
 		if (history()->unreadReactions().add(id, type)) {
-			history()->session().changes().historyUpdated(
-				history(),
-				Data::HistoryUpdate::Flag::UnreadReactions);
+			if (type == HistoryUnreadThings::AddType::New) {
+				history()->session().changes().messageUpdated(
+					this,
+					Data::MessageUpdate::Flag::NewUnreadReaction);
+			}
+			if (hasUnreadReaction()) {
+				history()->session().changes().historyUpdated(
+					history(),
+					Data::HistoryUpdate::Flag::UnreadReactions);
+			}
 		}
 	}
 }

Telegram/SourceFiles/history/history_widget.cpp

@@ -651,6 +651,12 @@ HistoryWidget::HistoryWidget(
 		}
 	}, lifetime());
 
+	session().changes().realtimeMessageUpdates(
+		MessageUpdateFlag::NewUnreadReaction
+	) | rpl::start_with_next([=](const Data::MessageUpdate &update) {
+		maybeMarkReactionsRead(update.item);
+	}, lifetime());
+
 	using MediaSwitch = Media::Player::Instance::Switch;
 	Media::Player::instance()->switchToNextEvents(
 	) | rpl::filter([=](const MediaSwitch &pair) {
@@ -2802,6 +2808,26 @@ void HistoryWidget::newItemAdded(not_null<HistoryItem*> item) {
 	_itemRevealPending.emplace(item);
 }
 
+void HistoryWidget::maybeMarkReactionsRead(not_null<HistoryItem*> item) {
+	if (!_historyInited || !_list) {
+		return;
+	}
+	const auto view = item->mainView();
+	const auto itemTop = _list->itemTop(view);
+	if (itemTop <= 0 || !doWeReadMentions()) {
+		return;
+	}
+	const auto reactionCenter
+		= view->reactionButtonParameters({}, {}).center.y();
+	const auto visibleTop = _scroll->scrollTop();
+	const auto visibleBottom = visibleTop + _scroll->height();
+	if (itemTop + reactionCenter < visibleTop
+		|| itemTop + view->height() > visibleBottom) {
+		return;
+	}
+	session().api().markContentsRead(item);
+}
+
 void HistoryWidget::unreadCountUpdated() {
 	if (_history->chatListUnreadMark()) {
 		crl::on_main(this, [=, history = _history] {

Telegram/SourceFiles/history/history_widget.h

@@ -423,6 +423,7 @@ private:
 	void cornerButtonsAnimationFinish();
 	void sendButtonClicked();
 	void newItemAdded(not_null<HistoryItem*> item);
+	void maybeMarkReactionsRead(not_null<HistoryItem*> item);
 
 	void updateCornerButtonsPositions();
 	void updateHistoryDownVisibility();