From c3ac50ad3e79b26d1d99bd222a7e43adb86c2c1e Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 26 Oct 2022 00:17:06 +0300
Subject: [PATCH] Make it possible to retrieve components and systems of a
 particular type

---
 source/game/entity.h | 15 ++++++++++++++-
 source/game/handle.h |  7 +++++++
 source/game/stage.h  | 16 ++++++++++++++--
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/source/game/entity.h b/source/game/entity.h
index c28cbe5..c4cf83c 100644
--- a/source/game/entity.h
+++ b/source/game/entity.h
@@ -36,6 +36,11 @@ public:
 	void add_component(Handle<Component>);
 	void remove_component(Handle<Component>);
 
+	template<typename T>
+	Handle<T> get_component();
+
+	Handle<Transform> get_transform() const { return transform; }
+
 	void add_child(Handle<Entity>);
 	void remove_child(Handle<Entity>);
 
@@ -43,10 +48,18 @@ public:
 	Handle<Entity> get_root();
 	const std::vector<Handle<Entity>> &get_children() const { return children; }
 	Stage &get_stage();
-	Handle<Transform> get_transform() const { return transform; }
 };
 
 
+template<typename T>
+inline Handle<T> Entity::get_component()
+{
+	for(Handle<Component> c: components)
+		if(Handle<T> tc = dynamic_handle_cast<T>(c))
+			return tc;
+	return nullptr;
+}
+
 inline Handle<Entity> Entity::get_root()
 {
 	Handle<Entity> e = Handle<Entity>::from_object(this);
diff --git a/source/game/handle.h b/source/game/handle.h
index 2e544c7..b08bcf8 100644
--- a/source/game/handle.h
+++ b/source/game/handle.h
@@ -39,6 +39,13 @@ public:
 	bool operator==(const Handle &other) const = default;
 };
 
+template<typename T, typename U>
+	requires std::is_base_of_v<U, T>
+Handle<T> dynamic_handle_cast(Handle<U> h)
+{
+	return Handle<T>::from_object(dynamic_cast<T *>(h.get()));
+}
+
 } // namespace Msp::Game
 
 #endif
diff --git a/source/game/stage.h b/source/game/stage.h
index 80e7a4b..d7793e2 100644
--- a/source/game/stage.h
+++ b/source/game/stage.h
@@ -45,22 +45,34 @@ public:
 
 	const std::vector<std::unique_ptr<System>> &get_systems() const { return systems; }
 
+	template<typename T>
+	T *get_system() const;
+
 	void tick(Time::TimeDelta);
 };
 
 template<typename T, typename F>
-void Stage::iterate_objects(const F &func)
+inline void Stage::iterate_objects(const F &func)
 {
 	pools.get_pool<T>().iterate_objects(func);
 }
 
 template<typename T, typename... Args>
-T &Stage::add_system(Args &&... args)
+inline T &Stage::add_system(Args &&... args)
 {
 	systems.emplace_back(std::make_unique<T>(*this, std::forward<Args>(args)...));
 	return static_cast<T &>(*systems.back());
 }
 
+template<typename T>
+inline T *Stage::get_system() const
+{
+	for(const auto &s: systems)
+		if(T *ts = dynamic_cast<T *>(s.get()))
+			return ts;
+	return nullptr;
+}
+
 } // namespace Msp::Game
 
 #endif
-- 
2.43.0