Add bt::on_event

libs/bt/include/psemek/bt/on_event.hpp

@@ -0,0 +1,64 @@
+#pragma once
+
+#include <psemek/bt/node.hpp>
+
+#include <optional>
+
+namespace psemek::bt
+{
+
+	template <typename Tree, typename EventFn>
+	struct on_event_node;
+
+	template <typename Time, typename Event, typename ... Args, typename EventFn>
+	struct on_event_node<tree<Time, Event, Args...>, EventFn>
+		: node<tree<Time, Event, Args...>>
+	{
+		using tree_type = tree<Time, Event, Args...>;
+		using node_type = node<tree_type>;
+		using typename node_type::status;
+
+		on_event_node(EventFn && event_fn, node_ptr<tree_type> child)
+			: event_fn_(std::move(event_fn))
+			, child_(std::move(child))
+		{}
+
+		void start(Args ... args) override
+		{
+			child_->start(args...);
+		}
+
+		status update(Time dt, Args ... args) override
+		{
+			if (cached_status_)
+			{
+				auto result = *cached_status_;
+				cached_status_ = std::nullopt;
+				return result;
+			}
+
+			return child_->update(dt, args...);
+		}
+
+		bool event(Event const & e, Args ... args) override
+		{
+			cached_status_ = event_fn_(e, args...);
+			if (cached_status_)
+				return true;
+			return child_->event(e, args...);
+		}
+
+
+	private:
+		EventFn event_fn_;
+		node_ptr<tree_type> child_;
+		std::optional<status> cached_status_;
+	};
+
+	template <typename Tree, typename EventFn>
+	node_ptr<Tree> on_event(EventFn && event_fn, node_ptr<Tree> child)
+	{
+		return std::make_unique<on_event_node<Tree, EventFn>>(std::move(event_fn), std::move(child));
+	}
+
+}