Use HistoryMedia as view, add Data::Media.

Telegram/SourceFiles/data/data_groups.cpp

@@ -0,0 +1,49 @@
+/*
+This file is part of Telegram Desktop,
+the official desktop application for the Telegram messaging service.
+
+For license and copyright information please follow this link:
+https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
+*/
+#include "data/data_groups.h"
+
+#include "history/history_item.h"
+
+namespace Data {
+
+void Groups::registerMessage(not_null<HistoryItem*> item) {
+	const auto groupId = item->groupId();
+	if (!groupId) {
+		return;
+	}
+	const auto i = _data.emplace(groupId, Group()).first;
+	i->second.items.push_back(item);
+}
+
+void Groups::unregisterMessage(not_null<HistoryItem*> item) {
+	const auto groupId = item->groupId();
+	if (!groupId) {
+		return;
+	}
+	const auto i = _data.find(groupId);
+	if (i != _data.end()) {
+		auto &group = i->second;
+		group.items.erase(
+			ranges::remove(group.items, item),
+			group.items.end());
+		if (group.items.empty()) {
+			_data.erase(i);
+		}
+	}
+}
+
+const Group *Groups::find(not_null<HistoryItem*> item) const {
+	const auto groupId = item->groupId();
+	if (!groupId) {
+		return nullptr;
+	}
+	const auto i = _data.find(groupId);
+	return (i != _data.end()) ? &i->second : nullptr;
+}
+
+} // namespace Data