merge `loek/tests` into `loek/cleanup` (close #32)

45 files changed, 316 insertions, 215 deletions

diff --git a/src/crepe/Collider.cpp b/src/crepe/Collider.cpp
index bbec488..113ba61 100644
--- a/src/crepe/Collider.cpp
+++ b/src/crepe/Collider.cpp
@@ -1,5 +1,3 @@
 #include "Collider.h"
 
 using namespace crepe;
-
-Collider::Collider(game_object_id_t id) : Component(id) {}
diff --git a/src/crepe/Collider.h b/src/crepe/Collider.h
index 827f83d..a1e9095 100644
--- a/src/crepe/Collider.h
+++ b/src/crepe/Collider.h
@@ -6,7 +6,7 @@ namespace crepe {
 
 class Collider : public Component {
 public:
-	Collider(game_object_id_t id);
+	using Component::Component;
 
 	int size;
 };
diff --git a/src/crepe/Component.cpp b/src/crepe/Component.cpp
index 73c2d07..acfd35c 100644
--- a/src/crepe/Component.cpp
+++ b/src/crepe/Component.cpp
@@ -1,5 +1,4 @@
 #include "Component.h"
-#include "types.h"
 
 using namespace crepe;
 
diff --git a/src/crepe/Component.h b/src/crepe/Component.h
index 0fe60b2..12c10cb 100644
--- a/src/crepe/Component.h
+++ b/src/crepe/Component.h
@@ -2,8 +2,6 @@
 
 #include "types.h"
 
-#include <cstdint>
-
 namespace crepe {
 
 class ComponentManager;
@@ -15,16 +13,21 @@ class ComponentManager;
  * interface for all components.
  */
 class Component {
+public:
+	//! Whether the component is active
+	bool active = true;
+	//! The id of the GameObject this component belongs to
+	const game_object_id_t game_object_id;
+
 protected:
-	//! Only the ComponentManager can create components
-	friend class crepe::ComponentManager;
 	/**
 	 * \param id The id of the GameObject this component belongs to
 	 */
 	Component(game_object_id_t id);
+	//! Only the ComponentManager can create components
+	friend class ComponentManager;
 
 public:
-	virtual ~Component() = default;
 	/**
 	 * \brief Get the maximum number of instances for this component
 	 *
@@ -35,12 +38,6 @@ public:
 	 * \return The maximum number of instances for this component
 	 */
 	virtual int get_instances_max() const { return -1; }
-
-public:
-	//! The id of the GameObject this component belongs to
-	const game_object_id_t game_object_id;
-	//! Whether the component is active
-	bool active = true;
 };
 
 } // namespace crepe
diff --git a/src/crepe/ComponentManager.cpp b/src/crepe/ComponentManager.cpp
index 7123905..c6b658c 100644
--- a/src/crepe/ComponentManager.cpp
+++ b/src/crepe/ComponentManager.cpp
@@ -1,13 +1,10 @@
+#include "api/GameObject.h"
 #include "util/Log.h"
 
 #include "ComponentManager.h"
 
 using namespace crepe;
-
-ComponentManager & ComponentManager::get_instance() {
-	static ComponentManager instance;
-	return instance;
-}
+using namespace std;
 
 void ComponentManager::delete_all_components_of_id(game_object_id_t id) {
 	// Loop through all the types (in the unordered_map<>)
@@ -26,5 +23,15 @@ void ComponentManager::delete_all_components() {
 }
 
 ComponentManager::ComponentManager() { dbg_trace(); }
-
 ComponentManager::~ComponentManager() { dbg_trace(); }
+
+GameObject & ComponentManager::new_object(const string & name,
+										  const string & tag,
+										  const Vector2 & position,
+										  double rotation, double scale) {
+	GameObject * object = new GameObject(*this, this->next_id, name, tag,
+										 position, rotation, scale);
+	this->objects.push_front(unique_ptr<GameObject>(object));
+	this->next_id++;
+	return *object;
+}
diff --git a/src/crepe/ComponentManager.h b/src/crepe/ComponentManager.h
index c8c196c..75606e0 100644
--- a/src/crepe/ComponentManager.h
+++ b/src/crepe/ComponentManager.h
@@ -1,15 +1,18 @@
 #pragma once
 
-#include <cstdint>
+#include <forward_list>
 #include <memory>
 #include <typeindex>
 #include <unordered_map>
 #include <vector>
 
 #include "Component.h"
+#include "api/Vector2.h"
 
 namespace crepe {
 
+class GameObject;
+
 /**
  * \brief Manages all components
  * 
@@ -18,18 +21,10 @@ namespace crepe {
  */
 class ComponentManager {
 public:
-	/**
-	 * \brief Get the instance of the ComponentManager
-	 * 
-	 * \return The instance of the ComponentManager
-	 */
-	static ComponentManager & get_instance();
-	ComponentManager(const ComponentManager &) = delete;
-	ComponentManager(ComponentManager &&) = delete;
-	ComponentManager & operator=(const ComponentManager &) = delete;
-	ComponentManager & operator=(ComponentManager &&) = delete;
-	~ComponentManager();
+	ComponentManager(); // dbg_trace
+	~ComponentManager(); // dbg_trace
 
+protected:
 	/**
 	 * \brief Add a component to the ComponentManager
 	 * 
@@ -44,6 +39,11 @@ public:
 	 */
 	template <typename T, typename... Args>
 	T & add_component(game_object_id_t id, Args &&... args);
+	//! GameObject is used as an interface to add components instead of the
+	// component manager directly
+	friend class GameObject;
+
+public:
 	/**
 	 * \brief Delete all components of a specific type and id
 	 * 
@@ -100,8 +100,11 @@ public:
 	template <typename T>
 	std::vector<std::reference_wrapper<T>> get_components_by_type() const;
 
-private:
-	ComponentManager();
+	// TODO: doxygen
+	GameObject & new_object(const std::string & name,
+							const std::string & tag = "",
+							const Vector2 & position = {0, 0},
+							double rotation = 0, double scale = 0);
 
 private:
 	/**
@@ -118,6 +121,10 @@ private:
 	std::unordered_map<std::type_index,
 					   std::vector<std::vector<std::unique_ptr<Component>>>>
 		components;
+
+	//! ID of next GameObject
+	game_object_id_t next_id = 0;
+	std::forward_list<std::unique_ptr<GameObject>> objects;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Animator.cpp b/src/crepe/api/Animator.cpp
index 863dce6..54b2ec3 100644
--- a/src/crepe/api/Animator.cpp
+++ b/src/crepe/api/Animator.cpp
@@ -9,7 +9,8 @@
 
 using namespace crepe;
 
-Animator::Animator(uint32_t id, Sprite & ss, int row, int col, int col_animator)
+Animator::Animator(game_object_id_t id, Sprite & ss, int row, int col,
+				   int col_animator)
 	: Component(id),
 	  spritesheet(ss),
 	  row(row),
diff --git a/src/crepe/api/Animator.h b/src/crepe/api/Animator.h
index def0240..75b8139 100644
--- a/src/crepe/api/Animator.h
+++ b/src/crepe/api/Animator.h
@@ -6,6 +6,7 @@
 #include "Sprite.h"
 
 namespace crepe {
+
 class AnimatorSystem;
 class SDLContext;
 
@@ -35,7 +36,7 @@ public:
 	 *
 	 * This constructor sets up the Animator with the given parameters, and initializes the animation system.
 	 */
-	Animator(uint32_t id, Sprite & spritesheet, int row, int col,
+	Animator(game_object_id_t id, Sprite & spritesheet, int row, int col,
 			 int col_animate);
 
 	~Animator(); // dbg_trace
diff --git a/src/crepe/api/AssetManager.h b/src/crepe/api/AssetManager.h
index dbfaef3..86a9902 100644
--- a/src/crepe/api/AssetManager.h
+++ b/src/crepe/api/AssetManager.h
@@ -56,7 +56,8 @@ public:
 	 * cache.
 	 */
 	template <typename T>
-	std::shared_ptr<T> cache(const std::string & file_path, bool reload = false);
+	std::shared_ptr<T> cache(const std::string & file_path,
+							 bool reload = false);
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/BehaviorScript.cpp b/src/crepe/api/BehaviorScript.cpp
index e69de29..7bbace0 100644
--- a/src/crepe/api/BehaviorScript.cpp
+++ b/src/crepe/api/BehaviorScript.cpp
@@ -0,0 +1,15 @@
+#include "BehaviorScript.h"
+#include "Component.h"
+#include "GameObject.h"
+
+using namespace crepe;
+
+BehaviorScript::BehaviorScript(game_object_id_t id, ComponentManager & mgr)
+	: Component(id),
+	  component_manager(mgr) {}
+
+template <>
+BehaviorScript & GameObject::add_component<BehaviorScript>() {
+	ComponentManager & mgr = this->component_manager;
+	return mgr.add_component<BehaviorScript>(this->id, mgr);
+}
diff --git a/src/crepe/api/BehaviorScript.h b/src/crepe/api/BehaviorScript.h
index 4160a72..2982358 100644
--- a/src/crepe/api/BehaviorScript.h
+++ b/src/crepe/api/BehaviorScript.h
@@ -3,6 +3,7 @@
 #include <memory>
 
 #include "../Component.h"
+#include "GameObject.h"
 
 namespace crepe {
 
@@ -19,22 +20,52 @@ class Script;
  */
 class BehaviorScript : public Component {
 protected:
-	friend class crepe::ComponentManager;
-	using Component::Component;
+	BehaviorScript(game_object_id_t id, ComponentManager & component_manager);
+	//! Only ComponentManager is allowed to instantiate BehaviorScript
+	friend class ComponentManager;
 
 public:
 	~BehaviorScript() = default;
 
 public:
+	/**
+	 * \brief Set the concrete script of this component
+	 *
+	 * \tparam T Concrete script type (derived from \c crepe::Script)
+	 *
+	 * \returns Reference to BehaviorScript component (`*this`)
+	 */
 	template <class T>
 	BehaviorScript & set_script();
 
 protected:
-	friend class crepe::ScriptSystem;
+	//! ScriptSystem needs direct access to the script instance
+	friend class ScriptSystem;
+	//! Flag to indicate if script->init() has been called already
+	bool initialized = false;
 	//! Script instance
 	std::unique_ptr<Script> script = nullptr;
+	//! Reference to component manager
+	ComponentManager & component_manager;
+
+private:
+	//! Script accesses the component manager directly via its parent
+	// (BehaviorScript) reference
+	friend class Script;
 };
 
+/**
+ * \brief Add a BehaviorScript component to this game object
+ *
+ * The \c BehaviorScript class is the only exception to the ECS harmony, and
+ * requires a reference to the component manager passed to its constructor in
+ * order to function normally. This is because the \c BehaviorScript (and \c
+ * Script) classes are the only component-related classes that store
+ * implemented member functions as data.
+ */
+template <>
+BehaviorScript & GameObject::add_component<BehaviorScript>();
+
 } // namespace crepe
 
 #include "BehaviorScript.hpp"
diff --git a/src/crepe/api/BehaviorScript.hpp b/src/crepe/api/BehaviorScript.hpp
index bc157fd..eec26da 100644
--- a/src/crepe/api/BehaviorScript.hpp
+++ b/src/crepe/api/BehaviorScript.hpp
@@ -11,10 +11,11 @@ namespace crepe {
 
 template <class T>
 BehaviorScript & BehaviorScript::set_script() {
-	static_assert(std::is_base_of<Script, T>::value);
 	dbg_trace();
+	static_assert(std::is_base_of<Script, T>::value);
 	Script * s = new T();
-	s->parent = this;
+	s->parent_ref = this;
+	s->component_manager_ref = &this->component_manager;
 	this->script = std::unique_ptr<Script>(s);
 	return *this;
 }
diff --git a/src/crepe/api/Camera.cpp b/src/crepe/api/Camera.cpp
index 6f0deb1..5835bdd 100644
--- a/src/crepe/api/Camera.cpp
+++ b/src/crepe/api/Camera.cpp
@@ -1,6 +1,3 @@
-
-#include <cstdint>
-
 #include "util/Log.h"
 
 #include "Camera.h"
@@ -9,7 +6,7 @@
 
 using namespace crepe;
 
-Camera::Camera(uint32_t id, const Color & bg_color)
+Camera::Camera(game_object_id_t id, const Color & bg_color)
 	: Component(id),
 	  bg_color(bg_color) {
 	dbg_trace();
diff --git a/src/crepe/api/Camera.h b/src/crepe/api/Camera.h
index ba3a9ef..d8c08a6 100644
--- a/src/crepe/api/Camera.h
+++ b/src/crepe/api/Camera.h
@@ -23,7 +23,7 @@ public:
 	 * \param id Unique identifier for the camera component.
 	 * \param bg_color Background color for the camera view.
 	 */
-	Camera(uint32_t id, const Color & bg_color);
+	Camera(game_object_id_t id, const Color & bg_color);
 	~Camera(); // dbg_trace only
 
 public:
diff --git a/src/crepe/api/GameObject.cpp b/src/crepe/api/GameObject.cpp
index d252e77..4f3c639 100644
--- a/src/crepe/api/GameObject.cpp
+++ b/src/crepe/api/GameObject.cpp
@@ -1,23 +1,27 @@
 #include "api/Transform.h"
 
+#include "BehaviorScript.h"
 #include "GameObject.h"
 #include "Metadata.h"
 
 using namespace crepe;
 using namespace std;
 
-GameObject::GameObject(game_object_id_t id, const std::string & name,
+GameObject::GameObject(ComponentManager & component_manager,
+					   game_object_id_t id, const std::string & name,
 					   const std::string & tag, const Vector2 & position,
 					   double rotation, double scale)
-	: id(id) {
+	: id(id),
+	  component_manager(component_manager) {
+
 	// Add Transform and Metadata components
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 	mgr.add_component<Transform>(this->id, position, rotation, scale);
 	mgr.add_component<Metadata>(this->id, name, tag);
 }
 
 void GameObject::set_parent(const GameObject & parent) {
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 
 	// Set parent on own Metadata component
 	vector<reference_wrapper<Metadata>> this_metadata
diff --git a/src/crepe/api/GameObject.h b/src/crepe/api/GameObject.h
index d703730..73ff0b8 100644
--- a/src/crepe/api/GameObject.h
+++ b/src/crepe/api/GameObject.h
@@ -2,11 +2,12 @@
 
 #include <string>
 
+#include "Vector2.h"
 #include "types.h"
 
 namespace crepe {
 
-class Vector2;
+class ComponentManager;
 
 /**
  * \brief Represents a GameObject
@@ -16,11 +17,12 @@ class Vector2;
  * done in the ComponentManager.
  */
 class GameObject {
-public:
+private:
 	/**
 	 * This constructor creates a new GameObject. It creates a new
 	 * Transform and Metadata component and adds them to the ComponentManager.
 	 * 
+	 * \param component_manager Reference to component_manager
 	 * \param id The id of the GameObject
 	 * \param name The name of the GameObject
 	 * \param tag The tag of the GameObject
@@ -28,9 +30,13 @@ public:
 	 * \param rotation The rotation of the GameObject
 	 * \param scale The scale of the GameObject
 	 */
-	GameObject(game_object_id_t id, const std::string & name,
-			   const std::string & tag, const Vector2 & position,
-			   double rotation, double scale);
+	GameObject(ComponentManager & component_manager, game_object_id_t id,
+			   const std::string & name, const std::string & tag,
+			   const Vector2 & position, double rotation, double scale);
+	//! ComponentManager instances GameObject
+	friend class ComponentManager;
+
+public:
 	/**
 	 * \brief Set the parent of this GameObject
 	 * 
@@ -58,6 +64,9 @@ public:
 public:
 	//! The id of the GameObject
 	const game_object_id_t id;
+
+protected:
+	ComponentManager & component_manager;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/GameObject.hpp b/src/crepe/api/GameObject.hpp
index bfba7fe..17b17d7 100644
--- a/src/crepe/api/GameObject.hpp
+++ b/src/crepe/api/GameObject.hpp
@@ -8,7 +8,7 @@ namespace crepe {
 
 template <typename T, typename... Args>
 T & GameObject::add_component(Args &&... args) {
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 	return mgr.add_component<T>(this->id, std::forward<Args>(args)...);
 }
 
diff --git a/src/crepe/api/LoopManager.cpp b/src/crepe/api/LoopManager.cpp
index 2e9823f..f0788ab 100644
--- a/src/crepe/api/LoopManager.cpp
+++ b/src/crepe/api/LoopManager.cpp
@@ -1,5 +1,9 @@
-
 #include "../facade/SDLContext.h"
+
+#include "../system/AnimatorSystem.h"
+#include "../system/CollisionSystem.h"
+#include "../system/ParticleSystem.h"
+#include "../system/PhysicsSystem.h"
 #include "../system/RenderSystem.h"
 #include "../system/ScriptSystem.h"
 
@@ -7,11 +11,25 @@
 #include "LoopTimer.h"
 
 using namespace crepe;
+using namespace std;
+
+LoopManager::LoopManager() {
+	this->load_system<AnimatorSystem>();
+	this->load_system<CollisionSystem>();
+	this->load_system<ParticleSystem>();
+	this->load_system<PhysicsSystem>();
+	this->load_system<RenderSystem>();
+	this->load_system<ScriptSystem>();
+}
+
+ComponentManager & LoopManager::get_component_manager() {
+	return this->component_manager;
+}
 
-LoopManager::LoopManager() {}
 void LoopManager::process_input() {
 	SDLContext::get_instance().handle_events(this->game_running);
 }
+
 void LoopManager::start() {
 	this->setup();
 	this->loop();
@@ -48,7 +66,7 @@ void LoopManager::setup() {
 
 void LoopManager::render() {
 	if (this->game_running) {
-		RenderSystem::get_instance().update();
+		this->get_system<RenderSystem>().update();
 	}
 }
 
diff --git a/src/crepe/api/LoopManager.h b/src/crepe/api/LoopManager.h
index 2f03193..288dca2 100644
--- a/src/crepe/api/LoopManager.h
+++ b/src/crepe/api/LoopManager.h
@@ -2,15 +2,9 @@
 
 #include <memory>
 
-class RenderSystem;
-class SDLContext;
-class LoopTimer;
-class ScriptSystem;
-class SoundSystem;
-class ParticleSystem;
-class PhysicsSystem;
-class AnimatorSystem;
-class CollisionSystem;
+#include "../ComponentManager.h"
+#include "../system/System.h"
+
 namespace crepe {
 
 class LoopManager {
@@ -73,7 +67,21 @@ private:
 	void render();
 
 	bool game_running = false;
-	//#TODO add system instances
+
+protected:
+	ComponentManager & get_component_manager();
+	template <class T>
+	T & get_system();
+
+private:
+	ComponentManager component_manager{};
+	std::unordered_map<std::type_index, std::unique_ptr<System>> systems;
+
+private:
+	template <class T>
+	void load_system();
 };
 
 } // namespace crepe
+
+#include "LoopManager.hpp"
diff --git a/src/crepe/api/LoopManager.hpp b/src/crepe/api/LoopManager.hpp
new file mode 100644
index 0000000..8fb9aa3
--- /dev/null
+++ b/src/crepe/api/LoopManager.hpp
@@ -0,0 +1,40 @@
+#pragma once
+
+#include <cassert>
+#include <memory>
+
+#include "../Exception.h"
+#include "../system/System.h"
+
+#include "LoopManager.h"
+
+namespace crepe {
+
+template <class T>
+T & LoopManager::get_system() {
+	using namespace std;
+	static_assert(is_base_of<System, T>::value,
+				  "get_system must recieve a derivative class of System");
+
+	const type_info & type = typeid(T);
+	if (!this->systems.contains(type))
+		throw Exception("LoopManager: %s is not initialized", type.name());
+
+	System * system = this->systems.at(type).get();
+	T * concrete_system = dynamic_cast<T *>(system);
+	assert(concrete_system != nullptr);
+
+	return *concrete_system;
+}
+
+template <class T>
+void LoopManager::load_system() {
+	using namespace std;
+	static_assert(is_base_of<System, T>::value,
+				  "load_system must recieve a derivative class of System");
+
+	System * system = new T(this->component_manager);
+	this->systems[typeid(T)] = unique_ptr<System>(system);
+}
+
+} // namespace crepe
diff --git a/src/crepe/api/Rigidbody.cpp b/src/crepe/api/Rigidbody.cpp
index 3bf1c5b..6b87695 100644
--- a/src/crepe/api/Rigidbody.cpp
+++ b/src/crepe/api/Rigidbody.cpp
@@ -2,8 +2,8 @@
 
 using namespace crepe;
 
-crepe::Rigidbody::Rigidbody(uint32_t game_object_id, const Data & data)
-	: Component(game_object_id),
+crepe::Rigidbody::Rigidbody(game_object_id_t id, const Data & data)
+	: Component(id),
 	  data(data) {}
 
 void crepe::Rigidbody::add_force_linear(const Vector2 & force) {
diff --git a/src/crepe/api/Rigidbody.h b/src/crepe/api/Rigidbody.h
index 68481f4..2e20288 100644
--- a/src/crepe/api/Rigidbody.h
+++ b/src/crepe/api/Rigidbody.h
@@ -82,7 +82,7 @@ public:
 	 * \param game_object_id id of the gameobject the rigibody is added to.
 	 * \param data struct to configure the rigidbody.
 	 */
-	Rigidbody(uint32_t game_object_id, const Data & data);
+	Rigidbody(game_object_id_t id, const Data & data);
 	//! struct to hold data of rigidbody
 	Data data;
 
diff --git a/src/crepe/api/SceneManager.cpp b/src/crepe/api/SceneManager.cpp
index dfed6ee..4a38787 100644
--- a/src/crepe/api/SceneManager.cpp
+++ b/src/crepe/api/SceneManager.cpp
@@ -8,10 +8,7 @@
 using namespace crepe;
 using namespace std;
 
-SceneManager & SceneManager::get_instance() {
-	static SceneManager instance;
-	return instance;
-}
+SceneManager::SceneManager(ComponentManager & mgr) : component_manager(mgr) {}
 
 void SceneManager::set_next_scene(const string & name) { next_scene = name; }
 
@@ -30,7 +27,7 @@ void SceneManager::load_next_scene() {
 	unique_ptr<Scene> & scene = *it;
 
 	// Delete all components of the current scene
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 	mgr.delete_all_components();
 
 	// Load the new scene
diff --git a/src/crepe/api/SceneManager.h b/src/crepe/api/SceneManager.h
index 1e0e670..553194f 100644
--- a/src/crepe/api/SceneManager.h
+++ b/src/crepe/api/SceneManager.h
@@ -8,14 +8,12 @@
 
 namespace crepe {
 
+class ComponentManager;
+
 class SceneManager {
 public:
-	// Singleton
-	static SceneManager & get_instance();
-	SceneManager(const SceneManager &) = delete;
-	SceneManager(SceneManager &&) = delete;
-	SceneManager & operator=(const SceneManager &) = delete;
-	SceneManager & operator=(SceneManager &&) = delete;
+	SceneManager(ComponentManager & mgr);
+	virtual ~SceneManager() = default;
 
 public:
 	/**
@@ -38,11 +36,11 @@ public:
 	void load_next_scene();
 
 private:
-	SceneManager() = default;
-
-private:
 	std::vector<std::unique_ptr<Scene>> scenes;
 	std::string next_scene;
+
+protected:
+	ComponentManager & component_manager;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Script.h b/src/crepe/api/Script.h
index e6fbb5c..68a46d7 100644
--- a/src/crepe/api/Script.h
+++ b/src/crepe/api/Script.h
@@ -6,6 +6,7 @@ namespace crepe {
 
 class ScriptSystem;
 class BehaviorScript;
+class ComponentManager;
 
 /**
  * \brief Script interface
@@ -14,6 +15,7 @@ class BehaviorScript;
  * added to game objects using the \c BehaviorScript component.
  */
 class Script {
+	//! ScriptSystem calls \c update()
 	friend class crepe::ScriptSystem;
 
 protected:
@@ -61,9 +63,19 @@ protected:
 	template <typename T>
 	std::vector<std::reference_wrapper<T>> get_components() const;
 
+protected:
+	// NOTE: Script must have a constructor without arguments so the game
+	// programmer doesn't need to manually add `using Script::Script` to their
+	// concrete script class.
+	Script() = default;
+	//! Only \c BehaviorScript instantiates Script
+	friend class BehaviorScript;
+
 private:
-	friend class crepe::BehaviorScript;
-	BehaviorScript * parent = nullptr;
+	// These references are set by BehaviorScript immediately after calling the
+	// constructor of Script.
+	BehaviorScript * parent_ref = nullptr;
+	ComponentManager * component_manager_ref = nullptr;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Script.hpp b/src/crepe/api/Script.hpp
index 7ec3ebe..aceb38b 100644
--- a/src/crepe/api/Script.hpp
+++ b/src/crepe/api/Script.hpp
@@ -21,8 +21,10 @@ T & Script::get_component() const {
 
 template <typename T>
 std::vector<std::reference_wrapper<T>> Script::get_components() const {
-	ComponentManager & mgr = ComponentManager::get_instance();
-	return mgr.get_components_by_id<T>(this->parent->game_object_id);
+	auto & parent = *this->parent_ref;
+	auto & mgr = *this->component_manager_ref;
+
+	return mgr.get_components_by_id<T>(parent.game_object_id);
 }
 
 } // namespace crepe
diff --git a/src/crepe/api/Transform.h b/src/crepe/api/Transform.h
index 756e45b..902dafa 100644
--- a/src/crepe/api/Transform.h
+++ b/src/crepe/api/Transform.h
@@ -14,28 +14,26 @@ namespace crepe {
  */
 class Transform : public Component {
 public:
+	//! Translation (shift)
+	Vector2 position = {0, 0};
+	//! Rotation, in degrees
+	double rotation = 0;
+	//! Multiplication factor
+	double scale = 0;
+
+protected:
 	/**
 	 * \param id The id of the GameObject this component belongs to
 	 * \param point The position of the GameObject
 	 * \param rotation The rotation of the GameObject
 	 * \param scale The scale of the GameObject
 	 */
-	Transform(game_object_id_t id, const Vector2 & point, double rotation,
-			  double scale);
-	/**
-	 * \brief Get the maximum number of instances for this component
-	 *
-	 * \return The maximum number of instances for this component
-	 */
+	Transform(game_object_id_t id, const Vector2 & point, double rotation = 0,
+			  double scale = 0);
+	//! There is always exactly one transform component per entity
 	virtual int get_instances_max() const { return 1; }
-
-public:
-	//! Translation (shift)
-	Vector2 position;
-	//! Rotation, in degrees
-	double rotation;
-	//! Multiplication factor
-	double scale;
+	//! ComponentManager instantiates all components
+	friend class ComponentManager;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Vector2.cpp b/src/crepe/api/Vector2.cpp
index 09bb59b..7da202a 100644
--- a/src/crepe/api/Vector2.cpp
+++ b/src/crepe/api/Vector2.cpp
@@ -1,57 +1,43 @@
 #include "Vector2.h"
 
-namespace crepe {
+using namespace crepe;
 
-// Constructor with initial values
-Vector2::Vector2(float x, float y) : x(x), y(y) {}
-
-// Subtracts another vector from this vector and returns the result.
 Vector2 Vector2::operator-(const Vector2 & other) const {
 	return {x - other.x, y - other.y};
 }
 
-// Adds another vector to this vector and returns the result.
 Vector2 Vector2::operator+(const Vector2 & other) const {
 	return {x + other.x, y + other.y};
 }
 
-// Multiplies this vector by a scalar and returns the result.
 Vector2 Vector2::operator*(float scalar) const {
 	return {x * scalar, y * scalar};
 }
 
-// Multiplies this vector by another vector element-wise and updates this vector.
 Vector2 & Vector2::operator*=(const Vector2 & other) {
 	x *= other.x;
 	y *= other.y;
 	return *this;
 }
 
-// Adds another vector to this vector and updates this vector.
 Vector2 & Vector2::operator+=(const Vector2 & other) {
 	x += other.x;
 	y += other.y;
 	return *this;
 }
 
-// Adds a scalar value to both components of this vector and updates this vector.
 Vector2 & Vector2::operator+=(float other) {
 	x += other;
 	y += other;
 	return *this;
 }
 
-// Returns the negation of this vector.
 Vector2 Vector2::operator-() const { return {-x, -y}; }
 
-// Checks if this vector is equal to another vector.
 bool Vector2::operator==(const Vector2 & other) const {
 	return x == other.x && y == other.y;
 }
 
-// Checks if this vector is not equal to another vector.
 bool Vector2::operator!=(const Vector2 & other) const {
 	return !(*this == other);
 }
-
-} // namespace crepe
diff --git a/src/crepe/api/Vector2.h b/src/crepe/api/Vector2.h
index 741951b..a069a57 100644
--- a/src/crepe/api/Vector2.h
+++ b/src/crepe/api/Vector2.h
@@ -2,19 +2,12 @@
 
 namespace crepe {
 
-//! Vector2 class
-class Vector2 {
-public:
+//! 2D vector
+struct Vector2 {
 	//! X component of the vector
-	float x;
+	float x = 0;
 	//! Y component of the vector
-	float y;
-
-	//! Default constructor
-	Vector2() = default;
-
-	//! Constructor with initial values
-	Vector2(float x, float y);
+	float y = 0;
 
 	//! Subtracts another vector from this vector and returns the result.
 	Vector2 operator-(const Vector2 & other) const;
diff --git a/src/crepe/facade/SDLContext.cpp b/src/crepe/facade/SDLContext.cpp
index aa15ef6..a68d940 100644
--- a/src/crepe/facade/SDLContext.cpp
+++ b/src/crepe/facade/SDLContext.cpp
@@ -159,7 +159,7 @@ SDLContext::texture_from_path(const std::string & path) {
 
 	SDL_Surface * tmp = IMG_Load(path.c_str());
 	if (tmp == nullptr) {
-		tmp = IMG_Load("../asset/texture/ERROR.png");	
+		tmp = IMG_Load("../asset/texture/ERROR.png");
 	}
 
 	std::unique_ptr<SDL_Surface, std::function<void(SDL_Surface *)>>
diff --git a/src/crepe/system/AnimatorSystem.cpp b/src/crepe/system/AnimatorSystem.cpp
index 1c101fa..9d18873 100644
--- a/src/crepe/system/AnimatorSystem.cpp
+++ b/src/crepe/system/AnimatorSystem.cpp
@@ -1,27 +1,17 @@
-
 #include <cstdint>
 #include <functional>
 #include <vector>
 
 #include "api/Animator.h"
 #include "facade/SDLContext.h"
-#include "util/Log.h"
 
 #include "AnimatorSystem.h"
 #include "ComponentManager.h"
 
 using namespace crepe;
 
-AnimatorSystem::AnimatorSystem() { dbg_trace(); }
-AnimatorSystem::~AnimatorSystem() { dbg_trace(); }
-
-AnimatorSystem & AnimatorSystem::get_instance() {
-	static AnimatorSystem instance;
-	return instance;
-}
-
 void AnimatorSystem::update() {
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 
 	std::vector<std::reference_wrapper<Animator>> animations
 		= mgr.get_components_by_type<Animator>();
diff --git a/src/crepe/system/AnimatorSystem.h b/src/crepe/system/AnimatorSystem.h
index 969e9d1..aa97084 100644
--- a/src/crepe/system/AnimatorSystem.h
+++ b/src/crepe/system/AnimatorSystem.h
@@ -17,16 +17,7 @@ namespace crepe {
 class AnimatorSystem : public System {
 
 public:
-	/**
-	 * \brief Retrieves the singleton instance of the AnimatorSystem.
-	 *
-	 * \return A reference to the single instance of the AnimatorSystem.
-	 *
-	 * This method ensures that there is only one instance of the AnimatorSystem, following the
-	 * singleton design pattern. It can be used to access the system globally.
-	 */
-	static AnimatorSystem & get_instance();
-
+	using System::System;
 	/**
 	 * \brief Updates the Animator components.
 	 *
@@ -34,11 +25,7 @@ public:
 	 * Animator components, moving the animations forward and managing their behavior (e.g., looping).
 	 */
 	void update() override;
-
-private:
-	// private because singleton
-	AnimatorSystem(); // dbg_trace
-	~AnimatorSystem(); // dbg_trace
+	// FIXME: never say "likely" in the documentation lmao
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/CMakeLists.txt b/src/crepe/system/CMakeLists.txt
index 4c18b87..d658b25 100644
--- a/src/crepe/system/CMakeLists.txt
+++ b/src/crepe/system/CMakeLists.txt
@@ -1,4 +1,5 @@
 target_sources(crepe PUBLIC
+	System.cpp
 	ParticleSystem.cpp
 	ScriptSystem.cpp
 	PhysicsSystem.cpp
diff --git a/src/crepe/system/CollisionSystem.cpp b/src/crepe/system/CollisionSystem.cpp
index 55e0fdc..c74ca1d 100644
--- a/src/crepe/system/CollisionSystem.cpp
+++ b/src/crepe/system/CollisionSystem.cpp
@@ -2,6 +2,4 @@
 
 using namespace crepe;
 
-CollisionSystem::CollisionSystem() {}
-
 void CollisionSystem::update() {}
diff --git a/src/crepe/system/CollisionSystem.h b/src/crepe/system/CollisionSystem.h
index 1e9f1aa..c1a70d8 100644
--- a/src/crepe/system/CollisionSystem.h
+++ b/src/crepe/system/CollisionSystem.h
@@ -1,11 +1,13 @@
 #pragma once
 
+#include "System.h"
+
 namespace crepe {
 
-class CollisionSystem {
+class CollisionSystem : public System {
 public:
-	CollisionSystem();
-	void update();
+	using System::System;
+	void update() override;
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/ParticleSystem.cpp b/src/crepe/system/ParticleSystem.cpp
index 397b586..fe02682 100644
--- a/src/crepe/system/ParticleSystem.cpp
+++ b/src/crepe/system/ParticleSystem.cpp
@@ -8,10 +8,8 @@
 
 using namespace crepe;
 
-ParticleSystem::ParticleSystem() : elapsed_time(0.0f) {}
-
 void ParticleSystem::update() {
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 	std::vector<std::reference_wrapper<ParticleEmitter>> emitters
 		= mgr.get_components_by_type<ParticleEmitter>();
 	float delta_time = 0.10;
diff --git a/src/crepe/system/ParticleSystem.h b/src/crepe/system/ParticleSystem.h
index 3ac1d3f..f171c62 100644
--- a/src/crepe/system/ParticleSystem.h
+++ b/src/crepe/system/ParticleSystem.h
@@ -2,17 +2,22 @@
 
 #include "../api/ParticleEmitter.h"
 
+#include "System.h"
+
 namespace crepe {
 
-class ParticleSystem {
+class ParticleSystem : public System {
 public:
-	ParticleSystem();
-	void update();
+	using System::System;
+	void update() override;
 
 private:
-	void emit_particle(ParticleEmitter & emitter); //emits a new particle
+	//! Emits a new particle
+	void emit_particle(ParticleEmitter & emitter);
 
-	float elapsed_time; //elapsed time since the last emission
+	//! Elapsed time since the last emission
+	float elapsed_time = 0.0;
+	// TODO: to std::chrono::duration
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/PhysicsSystem.cpp b/src/crepe/system/PhysicsSystem.cpp
index eb54ad3..da79707 100644
--- a/src/crepe/system/PhysicsSystem.cpp
+++ b/src/crepe/system/PhysicsSystem.cpp
@@ -11,7 +11,7 @@
 using namespace crepe;
 
 void PhysicsSystem::update() {
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 	std::vector<std::reference_wrapper<Rigidbody>> rigidbodies
 		= mgr.get_components_by_type<Rigidbody>();
 	std::vector<std::reference_wrapper<Transform>> transforms
diff --git a/src/crepe/system/PhysicsSystem.h b/src/crepe/system/PhysicsSystem.h
index cb6160e..5433a0f 100644
--- a/src/crepe/system/PhysicsSystem.h
+++ b/src/crepe/system/PhysicsSystem.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include "System.h"
+
 namespace crepe {
 
 /**
@@ -8,18 +10,15 @@ namespace crepe {
  * This class is a physics system that uses a rigidbody and transform
  * to add physics to a game object.
  */
-class PhysicsSystem {
+class PhysicsSystem : public System {
 public:
-	/**
-	 * Constructor is default
-	 */
-	PhysicsSystem() = default;
+	using System::System;
 	/**
 	 * \brief updates the physics system.
 	 * 
 	 * It calculates new velocties and changes the postion in the transform.
 	 */
-	void update();
+	void update() override;
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/RenderSystem.cpp b/src/crepe/system/RenderSystem.cpp
index 3ff5b4f..0d37808 100644
--- a/src/crepe/system/RenderSystem.cpp
+++ b/src/crepe/system/RenderSystem.cpp
@@ -11,15 +11,6 @@
 
 using namespace crepe;
 
-RenderSystem::RenderSystem() { dbg_trace(); }
-
-RenderSystem::~RenderSystem() { dbg_trace(); }
-
-RenderSystem & RenderSystem::get_instance() {
-	static RenderSystem instance;
-	return instance;
-}
-
 void RenderSystem::clear_screen() const {
 	SDLContext::get_instance().clear_screen();
 }
@@ -28,7 +19,7 @@ void RenderSystem::present_screen() const {
 	SDLContext::get_instance().present_screen();
 }
 void RenderSystem::update_camera() {
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 
 	std::vector<std::reference_wrapper<Camera>> cameras
 		= mgr.get_components_by_type<Camera>();
@@ -39,8 +30,7 @@ void RenderSystem::update_camera() {
 	}
 }
 void RenderSystem::render_sprites() const {
-
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 
 	std::vector<std::reference_wrapper<Sprite>> sprites
 		= mgr.get_components_by_type<Sprite>();
diff --git a/src/crepe/system/RenderSystem.h b/src/crepe/system/RenderSystem.h
index 70db21a..da4e910 100644
--- a/src/crepe/system/RenderSystem.h
+++ b/src/crepe/system/RenderSystem.h
@@ -15,14 +15,8 @@ namespace crepe {
  * rendering services for the application.
  */
 class RenderSystem : public System {
-
 public:
-	/**
-	 * \brief Gets the singleton instance of RenderSystem.
-	 * \return Reference to the RenderSystem instance.
-	 */
-	static RenderSystem & get_instance();
-
+	using System::System;
 	/**
 	 * \brief Updates the RenderSystem for the current frame.
 	 * This method is called to perform all rendering operations for the current game frame.
@@ -30,10 +24,6 @@ public:
 	void update() override;
 
 private:
-	// Private constructor to enforce singleton pattern.
-	RenderSystem();
-	~RenderSystem();
-
 	//! Clears the screen in preparation for rendering.
 	void clear_screen() const;
 
@@ -61,4 +51,5 @@ private:
 	Camera * curr_cam = nullptr;
 	// TODO: needs a better solution
 };
+
 } // namespace crepe
diff --git a/src/crepe/system/ScriptSystem.cpp b/src/crepe/system/ScriptSystem.cpp
index 807ad7f..7b22533 100644
--- a/src/crepe/system/ScriptSystem.cpp
+++ b/src/crepe/system/ScriptSystem.cpp
@@ -5,7 +5,6 @@
 #include "../ComponentManager.h"
 #include "../api/BehaviorScript.h"
 #include "../api/Script.h"
-#include "../util/Log.h"
 
 #include "ScriptSystem.h"
 
@@ -13,16 +12,24 @@ using namespace std;
 using namespace crepe;
 
 void ScriptSystem::update() {
-	using namespace std;
 	dbg_trace();
 
-	forward_list<Script *> scripts = this->get_scripts();
-	for (Script * script : scripts) script->update();
+	forward_list<reference_wrapper<Script>> scripts = this->get_scripts();
+
+	for (auto & script_ref : scripts) {
+		Script & script = script_ref.get();
+		BehaviorScript & component = *script.parent_ref;
+		if (!component.initialized) {
+			script.init();
+			component.initialized = true;
+		}
+		script.update();
+	}
 }
 
-forward_list<Script *> ScriptSystem::get_scripts() const {
-	forward_list<Script *> scripts = {};
-	ComponentManager & mgr = ComponentManager::get_instance();
+forward_list<reference_wrapper<Script>> ScriptSystem::get_scripts() const {
+	forward_list<reference_wrapper<Script>> scripts = {};
+	ComponentManager & mgr = this->component_manager;
 	vector<reference_wrapper<BehaviorScript>> behavior_scripts
 		= mgr.get_components_by_type<BehaviorScript>();
 
@@ -31,8 +38,9 @@ forward_list<Script *> ScriptSystem::get_scripts() const {
 		if (!behavior_script.active) continue;
 		Script * script = behavior_script.script.get();
 		if (script == nullptr) continue;
-		scripts.push_front(script);
+		scripts.push_front(*script);
 	}
 
 	return scripts;
 }
+
diff --git a/src/crepe/system/ScriptSystem.h b/src/crepe/system/ScriptSystem.h
index 9d57640..deb89cb 100644
--- a/src/crepe/system/ScriptSystem.h
+++ b/src/crepe/system/ScriptSystem.h
@@ -16,6 +16,7 @@ class Script;
  */
 class ScriptSystem : public System {
 public:
+	using System::System;
 	/**
 	 * \brief Call Script::update() on all active \c BehaviorScript instances
 	 *
@@ -23,17 +24,16 @@ public:
 	 * method. It also calls Script::init() if this has not been done before on
 	 * the \c BehaviorScript instance.
 	 */
-	void update();
+	void update() override;
 
 private:
-	// TODO: to forward_list<reference_wrapper>
 	/**
 	 * \brief Aggregate all active \c BehaviorScript components and return a list
 	 * of references to their \c Script instances (utility)
 	 *
 	 * \returns List of active \c Script instances
 	 */
-	std::forward_list<Script *> get_scripts() const;
+	std::forward_list<std::reference_wrapper<Script>> get_scripts() const;
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/System.cpp b/src/crepe/system/System.cpp
new file mode 100644
index 0000000..937a423
--- /dev/null
+++ b/src/crepe/system/System.cpp
@@ -0,0 +1,7 @@
+#include "../util/Log.h"
+
+#include "System.h"
+
+using namespace crepe;
+
+System::System(ComponentManager & mgr) : component_manager(mgr) { dbg_trace(); }
diff --git a/src/crepe/system/System.h b/src/crepe/system/System.h
index ec4507f..28ea20e 100644
--- a/src/crepe/system/System.h
+++ b/src/crepe/system/System.h
@@ -2,6 +2,8 @@
 
 namespace crepe {
 
+class ComponentManager;
+
 /**
  * \brief Base ECS system class
  *
@@ -17,8 +19,11 @@ public:
 	virtual void update() = 0;
 
 public:
-	System() = default;
+	System(ComponentManager &);
 	virtual ~System() = default;
+
+protected:
+	ComponentManager & component_manager;
 };
 
 } // namespace crepe