Track and display unread count in discussions.

Telegram/SourceFiles/data/data_changes.h

@@ -134,16 +134,17 @@ struct MessageUpdate {
 	enum class Flag : uint32 {
 		None = 0,
 
-		Edited           = (1U << 0),
-		Destroyed        = (1U << 1),
-		DialogRowRepaint = (1U << 2),
-		DialogRowRefresh = (1U << 3),
-		NewAdded         = (1U << 4),
-		ReplyMarkup      = (1U << 5),
-		BotCallbackSent  = (1U << 6),
-		NewMaybeAdded    = (1U << 7),
+		Edited             = (1U << 0),
+		Destroyed          = (1U << 1),
+		DialogRowRepaint   = (1U << 2),
+		DialogRowRefresh   = (1U << 3),
+		NewAdded           = (1U << 4),
+		ReplyMarkup        = (1U << 5),
+		BotCallbackSent    = (1U << 6),
+		NewMaybeAdded      = (1U << 7),
+		RepliesUnreadCount = (1U << 8),
 
-		LastUsedBit      = (1U << 7),
+		LastUsedBit        = (1U << 7),
 	};
 	using Flags = base::flags<Flag>;
 	friend inline constexpr auto is_flag_type(Flag) { return true; }

Telegram/SourceFiles/data/data_replies_list.cpp

@@ -101,6 +101,15 @@ rpl::producer<MessagesSlice> RepliesList::source(
 		_partLoaded.events(
 		) | rpl::start_with_next(pushDelayed, lifetime);
 
+		_history->session().data().channelDifferenceTooLong(
+		) | rpl::filter([=](not_null<ChannelData*> channel) {
+			if (_history->peer != channel || !_skippedAfter.has_value()) {
+				return false;
+			}
+			_skippedAfter = std::nullopt;
+			return true;
+		}) | rpl::start_with_next(pushDelayed, lifetime);
+
 		push();
 		return lifetime;
 	};
@@ -169,6 +178,64 @@ rpl::producer<int> RepliesList::fullCount() const {
 	return _fullCount.value() | rpl::filter_optional();
 }
 
+std::optional<int> RepliesList::fullUnreadCountAfter(
+		MsgId readTillId,
+		MsgId wasReadTillId,
+		std::optional<int> wasUnreadCountAfter) const {
+	Expects(readTillId >= wasReadTillId);
+
+	readTillId = std::max(readTillId, _rootId);
+	wasReadTillId = std::max(wasReadTillId, _rootId);
+	const auto backLoaded = (_skippedBefore == 0);
+	const auto frontLoaded = (_skippedAfter == 0);
+	const auto fullLoaded = backLoaded && frontLoaded;
+	const auto allUnread = (readTillId == _rootId)
+		|| (fullLoaded && _list.empty());
+	const auto countIncoming = [&](auto from, auto till) {
+		auto &owner = _history->owner();
+		const auto channelId = _history->channelId();
+		auto count = 0;
+		for (auto i = from; i != till; ++i) {
+			if (!owner.message(channelId, *i)->out()) {
+				++count;
+			}
+		}
+		return count;
+	};
+	if (allUnread && fullLoaded) {
+		// Should not happen too often unless the list is empty.
+		return countIncoming(begin(_list), end(_list));
+	} else if (frontLoaded && !_list.empty() && readTillId >= _list.front()) {
+		// Always "count by local data" if read till the end.
+		return 0;
+	} else if (wasReadTillId == readTillId) {
+		// Otherwise don't recount the same value over and over.
+		return wasUnreadCountAfter;
+	} else if (frontLoaded && !_list.empty() && readTillId >= _list.back()) {
+		// And count by local data if it is available and read-till changed.
+		return countIncoming(
+			begin(_list),
+			ranges::lower_bound(_list, readTillId, std::greater<>()));
+	} else if (_list.empty()) {
+		return std::nullopt;
+	} else if (wasUnreadCountAfter.has_value()
+		&& (frontLoaded || readTillId <= _list.front())
+		&& (backLoaded || wasReadTillId >= _list.back())) {
+		// Count how many were read since previous value.
+		const auto from = ranges::lower_bound(
+			_list,
+			readTillId,
+			std::greater<>());
+		const auto till = ranges::lower_bound(
+			from,
+			end(_list),
+			wasReadTillId,
+			std::greater<>());
+		return std::max(*wasUnreadCountAfter - countIncoming(from, till), 0);
+	}
+	return std::nullopt;
+}
+
 void RepliesList::injectRootMessageAndReverse(not_null<Viewer*> viewer) {
 	injectRootMessage(viewer);
 	ranges::reverse(viewer->slice.ids);

Telegram/SourceFiles/data/data_replies_list.h

@@ -31,6 +31,11 @@ public:
 
 	[[nodiscard]] rpl::producer<int> fullCount() const;
 
+	[[nodiscard]] std::optional<int> fullUnreadCountAfter(
+		MsgId readTillId,
+		MsgId wasReadTillId,
+		std::optional<int> wasUnreadCountAfter) const;
+
 private:
 	struct Viewer;