From 02b29af95a29a72a2efbc9a82041153711461265 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sat, 24 Jul 2021 11:14:39 +0300
Subject: [PATCH] Introduce util::ecs::behavior::context

---
 libs/util/include/psemek/util/ecs.hpp | 68 +++++++++++++++++----------
 1 file changed, 43 insertions(+), 25 deletions(-)

diff --git a/libs/util/include/psemek/util/ecs.hpp b/libs/util/include/psemek/util/ecs.hpp
index dc0dff52..04b81abf 100644
--- a/libs/util/include/psemek/util/ecs.hpp
+++ b/libs/util/include/psemek/util/ecs.hpp
@@ -23,7 +23,12 @@ namespace psemek::util
 
 		struct species_base
 		{
-			virtual std::string_view name() const = 0;
+			species_base(std::string name, handle id)
+				: name_(std::move(name))
+				, id_(id)
+			{}
+
+			std::string_view name() const { return name_; }
 
 			virtual void * get_species_component(std::type_index component_type) = 0;
 			virtual void * get_entity_component(std::type_index component_type) = 0;
@@ -65,6 +70,9 @@ namespace psemek::util
 
 		private:
 
+			std::string name_;
+			handle id_;
+
 			template <typename Behavior, typename ... Components, std::size_t ... Is>
 			void apply_impl(Behavior & behavior, std::tuple<Components...> *, std::index_sequence<Is...>)
 			{
@@ -80,15 +88,16 @@ namespace psemek::util
 				if (!std::apply(all_nonzero, cptrs))
 					return;
 
-				std::tuple<Components *...> cs;
+				typename Behavior::context ctx;
+				ctx.species = id_;
 
-				((std::get<Components *>(cs) = get_species_component<Components>()), ...);
+				((std::get<Components *>(ctx.components) = get_species_component<Components>()), ...);
 
 				auto visit = [&](auto * ... ptrs)
 				{
-					if constexpr (std::is_invocable_v<Behavior, typename Components::data & ..., std::tuple<Components *...> const &>)
+					if constexpr (std::is_invocable_v<Behavior, typename Components::data & ..., typename Behavior::context &>)
 					{
-						behavior(*ptrs..., cs);
+						behavior(*ptrs..., ctx);
 					}
 					else
 					{
@@ -108,7 +117,10 @@ namespace psemek::util
 				for (std::size_t i = 0; i < count; ++i)
 				{
 					if (*list == i)
+					{
+						ctx.entity = i;
 						std::apply(visit, cptrs);
+					}
 					std::apply(increment, cptrs);
 					++list;
 				}
@@ -119,16 +131,11 @@ namespace psemek::util
 		struct species_impl
 			: species_base
 		{
-			species_impl(std::string name, Components && ... components)
-				: name_(std::move(name))
+			species_impl(std::string name, handle id, Components && ... components)
+				: species_base(std::move(name), id)
 				, species_components_{std::move(components)...}
 			{}
 
-			std::string_view name() const override
-			{
-				return name_;
-			}
-
 			using species_base::get_species_component;
 			using species_base::get_entity_component;
 
@@ -170,7 +177,6 @@ namespace psemek::util
 			}
 
 		private:
-			std::string name_;
 			std::tuple<Components...> species_components_;
 			std::tuple<std::vector<typename Components::data>...> entity_components_;
 			std::vector<handle> list_;
@@ -220,12 +226,6 @@ namespace psemek::util
 			}
 		};
 
-		template <typename Behavior>
-		using prepare_helper = decltype(std::declval<Behavior>().prepare());
-
-		template <typename Behavior>
-		using has_prepare = std::experimental::is_detected<prepare_helper, Behavior>;
-
 	}
 
 	struct ecs
@@ -235,6 +235,20 @@ namespace psemek::util
 		{
 			using component_types = std::tuple<Components...>;
 			using component_ptrs = std::tuple<Components *...>;
+
+			struct context
+			{
+				ecs_detail::handle species;
+				ecs_detail::handle entity;
+
+				component_ptrs components;
+
+				template <typename Component>
+				Component & get() const
+				{
+					return *std::get<Component *>(components);
+				}
+			};
 		};
 
 		using handle = ecs_detail::handle;
@@ -280,6 +294,9 @@ namespace psemek::util
 		template <typename Behavior>
 		void apply(Behavior && behavior) const;
 
+		template <typename Behavior>
+		void apply(Behavior && behavior, handle species) const;
+
 	private:
 		std::vector<std::unique_ptr<ecs_detail::species_base>> species_;
 	};
@@ -288,7 +305,7 @@ namespace psemek::util
 	ecs::handle ecs::register_species(std::string name, Components && ... components)
 	{
 		handle result = species_.size();
-		species_.push_back(std::make_unique<ecs_detail::species_impl<Components...>>(std::move(name), std::move(components)...));
+		species_.push_back(std::make_unique<ecs_detail::species_impl<Components...>>(std::move(name), result, std::move(components)...));
 		return result;
 	}
 
@@ -372,13 +389,14 @@ namespace psemek::util
 	template <typename Behavior>
 	void ecs::apply(Behavior && behavior) const
 	{
-		if constexpr (ecs_detail::has_prepare<Behavior>::value)
-		{
-			behavior.prepare();
-		}
-
 		for (auto & s : species_)
 			s->apply(behavior);
 	}
 
+	template <typename Behavior>
+	void ecs::apply(Behavior && behavior, handle species) const
+	{
+		species_[species]->apply(behavior);
+	}
+
 }