Add bt::by_index node

libs/bt/include/psemek/bt/by_index.hpp

@@ -0,0 +1,65 @@
+#pragma once
+
+#include <psemek/bt/node.hpp>
+
+#include <vector>
+
+namespace psemek::bt
+{
+
+	template <typename Tree, typename IndexFn>
+	struct by_index_node;
+
+	template <typename Time, typename Event, typename ... Args, typename IndexFn>
+	struct by_index_node<tree<Time, Event, Args...>, IndexFn>
+		: node<tree<Time, Event, Args...>>
+	{
+		using tree_type = tree<Time, Event, Args...>;
+		using node_type = node<tree_type>;
+		using typename node_type::finished;
+		using typename node_type::status;
+
+		by_index_node(IndexFn && index_fn, std::vector<node_ptr<tree_type>> children)
+			: index_fn_(std::move(index_fn))
+			, children_(std::move(children))
+		{}
+
+		void start(Args ... args) override
+		{
+			current_index_ = index_fn_(args...);
+			if (current_index_ < children_.size())
+				children_[current_index_]->start(args...);
+		}
+
+		status update(Time dt, Args ... args) override
+		{
+			if (current_index_ >= children_.size())
+				return finished{false};
+
+			return children_[current_index_]->update(dt, args...);
+		}
+
+		bool event(Event const & event, Args ... args) override
+		{
+			if (current_index_ < children_.size())
+				return children_[current_index_]->event(event, args...);
+
+			return false;
+		}
+
+	private:
+		IndexFn index_fn_;
+		std::vector<node_ptr<tree_type>> children_;
+		std::size_t current_index_ = 0;
+	};
+
+	template <typename Tree, typename IndexFn, typename ... Nodes>
+	node_ptr<Tree> by_index(IndexFn && index_fn, node_ptr<Tree> child, Nodes && ... other_children)
+	{
+		std::vector<node_ptr<Tree>> children;
+		children.push_back(std::move(child));
+		(children.push_back(std::move(other_children)), ...);
+		return std::make_unique<by_index_node<Tree, IndexFn>>(std::move(index_fn), std::move(children));
+	}
+
+}