From ebafb55b1b9b93667546dec19ca92c99a3357eaf Mon Sep 17 00:00:00 2001
From: John Preston <johnprestonmail@gmail.com>
Date: Wed, 21 Jun 2023 13:35:10 +0400
Subject: [PATCH] Cache stories sources order in viewer.

---
 .../stories/media_stories_controller.cpp      | 78 +++++++++++++++++--
 .../media/stories/media_stories_controller.h  | 11 ++-
 2 files changed, 78 insertions(+), 11 deletions(-)

diff --git a/Telegram/SourceFiles/media/stories/media_stories_controller.cpp b/Telegram/SourceFiles/media/stories/media_stories_controller.cpp
index 5e71fcad07..79828f7fc2 100644
--- a/Telegram/SourceFiles/media/stories/media_stories_controller.cpp
+++ b/Telegram/SourceFiles/media/stories/media_stories_controller.cpp
@@ -618,7 +618,8 @@ void Controller::rebuildFromContext(
 			storyId.peer,
 			&StoriesSourceInfo::id);
 		if (i != end(sources)) {
-			showSiblings(&user->session(), sources, (i - begin(sources)));
+			rebuildCachedSourcesList(sources, (i - begin(sources)));
+			showSiblings(&user->session());
 			if (int(sources.end() - i) < kPreloadUsersCount) {
 				stories.loadMore(list);
 			}
@@ -780,18 +781,19 @@ void Controller::setPlayingAllowed(bool allowed) {
 	}
 }
 
-void Controller::showSiblings(
-		not_null<Main::Session*> session,
-		const std::vector<Data::StoriesSourceInfo> &sources,
-		int index) {
+void Controller::showSiblings(not_null<Main::Session*> session) {
 	showSibling(
 		_siblingLeft,
 		session,
-		(index > 0) ? sources[index - 1].id : PeerId());
+		(_cachedSourceIndex > 0
+			? _cachedSourcesList[_cachedSourceIndex - 1]
+			: PeerId()));
 	showSibling(
 		_siblingRight,
 		session,
-		(index + 1 < sources.size()) ? sources[index + 1].id : PeerId());
+		(_cachedSourceIndex + 1 < _cachedSourcesList.size()
+			? _cachedSourcesList[_cachedSourceIndex + 1]
+			: PeerId()));
 }
 
 void Controller::hideSiblings() {
@@ -1116,6 +1118,68 @@ void Controller::loadMoreToList() {
 	});
 }
 
+void Controller::rebuildCachedSourcesList(
+		const std::vector<Data::StoriesSourceInfo> &lists,
+		int index) {
+	Expects(index >= 0 && index < lists.size());
+
+	// Remove removed.
+	_cachedSourcesList.erase(ranges::remove_if(_cachedSourcesList, [&](
+			PeerId id) {
+		return !ranges::contains(lists, id, &Data::StoriesSourceInfo::id);
+	}), end(_cachedSourcesList));
+
+	// Find current, full rebuild if can't find.
+	const auto i = ranges::find(_cachedSourcesList, lists[index].id);
+	if (i == end(_cachedSourcesList)) {
+		_cachedSourcesList.clear();
+	} else {
+		_cachedSourceIndex = int(i - begin(_cachedSourcesList));
+	}
+
+	if (_cachedSourcesList.empty()) {
+		// Full rebuild.
+		_cachedSourcesList = lists
+			| ranges::views::transform(&Data::StoriesSourceInfo::id)
+			| ranges::to_vector;
+		_cachedSourceIndex = index;
+	} else if (ranges::equal(
+			lists,
+			_cachedSourcesList,
+			ranges::equal_to(),
+			&Data::StoriesSourceInfo::id)) {
+		// No rebuild needed.
+		_cachedSourceIndex = index;
+	} else {
+		// All that go before the current push to front.
+		for (auto before = index; before > 0;) {
+			--before;
+			const auto peerId = lists[--before].id;
+			if (!ranges::contains(_cachedSourcesList, peerId)) {
+				_cachedSourcesList.insert(
+					begin(_cachedSourcesList),
+					peerId);
+				++_cachedSourceIndex;
+			}
+		}
+		// All that go after the current push to back.
+		for (auto after = index + 1, count = int(lists.size()); after != count; ++after) {
+			const auto peerId = lists[after].id;
+			if (!ranges::contains(_cachedSourcesList, peerId)) {
+				_cachedSourcesList.push_back(peerId);
+			}
+		}
+	}
+
+	Ensures(_cachedSourcesList.size() == lists.size());
+	Ensures(ranges::equal(
+		lists,
+		_cachedSourcesList,
+		ranges::equal_to(),
+		&Data::StoriesSourceInfo::id));
+	Ensures(_cachedSourceIndex >= 0 && _cachedSourceIndex < _cachedSourcesList.size());
+}
+
 void Controller::refreshViewsFromData() {
 	Expects(shown());
 
diff --git a/Telegram/SourceFiles/media/stories/media_stories_controller.h b/Telegram/SourceFiles/media/stories/media_stories_controller.h
index 96d1020736..405960f39e 100644
--- a/Telegram/SourceFiles/media/stories/media_stories_controller.h
+++ b/Telegram/SourceFiles/media/stories/media_stories_controller.h
@@ -162,10 +162,7 @@ private:
 	void setPlayingAllowed(bool allowed);
 
 	void hideSiblings();
-	void showSiblings(
-		not_null<Main::Session*> session,
-		const std::vector<Data::StoriesSourceInfo> &lists,
-		int index);
+	void showSiblings(not_null<Main::Session*> session);
 	void showSibling(
 		std::unique_ptr<Sibling> &sibling,
 		not_null<Main::Session*> session,
@@ -186,6 +183,9 @@ private:
 	void rebuildFromContext(not_null<UserData*> user, FullStoryId storyId);
 	void checkMoveByDelta();
 	void loadMoreToList();
+	void rebuildCachedSourcesList(
+		const std::vector<Data::StoriesSourceInfo> &lists,
+		int index);
 
 	void startReactionAnimation(
 		Data::ReactionId id,
@@ -227,6 +227,9 @@ private:
 	bool _started = false;
 	bool _viewed = false;
 
+	std::vector<PeerId> _cachedSourcesList;
+	int _cachedSourceIndex = -1;
+
 	ViewsSlice _viewsSlice;
 	rpl::event_stream<> _moreViewsLoaded;
 	base::has_weak_ptr _viewsLoadGuard;