Implement PoC custom reaction selection.

Telegram/SourceFiles/data/data_message_reaction_id.h

@@ -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
+*/
+#pragma once
+
+namespace Data {
+
+struct ReactionId {
+	std::variant<QString, DocumentId> data;
+
+	[[nodiscard]] bool empty() const {
+		const auto emoji = std::get_if<QString>(&data);
+		return emoji && emoji->isEmpty();
+	}
+	[[nodiscard]] QString emoji() const {
+		const auto emoji = std::get_if<QString>(&data);
+		return emoji ? *emoji : QString();
+	}
+	[[nodiscard]] DocumentId custom() const {
+		const auto custom = std::get_if<DocumentId>(&data);
+		return custom ? *custom : DocumentId();
+	}
+};
+Q_DECLARE_METATYPE(ReactionId);
+
+inline bool operator<(const ReactionId &a, const ReactionId &b) {
+	return a.data < b.data;
+}
+inline bool operator==(const ReactionId &a, const ReactionId &b) {
+	return a.data == b.data;
+}
+
+[[nodiscard]] ReactionId ReactionFromMTP(const MTPReaction &reaction);
+[[nodiscard]] MTPReaction ReactionToMTP(ReactionId id);
+
+struct ReactionsFilter {
+	std::optional<base::flat_set<QString>> allowed;
+	bool customAllowed = false;
+
+	friend inline auto operator<=>(
+		const ReactionsFilter &,
+		const ReactionsFilter &) = default;
+};
+
+} // namespace Data