24 files changed, 809 insertions, 82 deletions

diff --git a/src/crepe/Component.h b/src/crepe/Component.h
index 060ff00..eff5a58 100644
--- a/src/crepe/Component.h
+++ b/src/crepe/Component.h
@@ -50,8 +50,6 @@ public:
 	 * \return The maximum number of instances for this component
 	 */
 	virtual int get_instances_max() const { return -1; }
-	//! Only ComponentManager needs to know the max instance count
-	friend class ComponentManager;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/AI.cpp b/src/crepe/api/AI.cpp
new file mode 100644
index 0000000..2195249
--- /dev/null
+++ b/src/crepe/api/AI.cpp
@@ -0,0 +1,89 @@
+#include <stdexcept>
+#include <type_traits>
+
+#include "AI.h"
+#include "types.h"
+
+namespace crepe {
+
+AI::AI(game_object_id_t id, float max_force) : Component(id), max_force(max_force) {}
+
+void AI::make_circle_path(float radius, const vec2 & center, float start_angle,
+						  bool clockwise) {
+	if (radius <= 0) {
+		throw std::runtime_error("Radius must be greater than 0");
+	}
+
+	// The step size is determined by the radius (step size is in radians)
+	float step = RADIUS_TO_STEP / radius;
+	// Force at least MIN_STEP steps (in case of a small radius)
+	if (step > 2 * M_PI / MIN_STEP) {
+		step = 2 * M_PI / MIN_STEP;
+	}
+	// The path node distance is determined by the step size and the radius
+	this->path_node_distance = radius * step * PATH_NODE_DISTANCE_FACTOR;
+
+	if (clockwise) {
+		for (float i = start_angle; i < 2 * M_PI + start_angle; i += step) {
+			path.push_back(vec2{static_cast<float>(center.x + radius * cos(i)),
+								static_cast<float>(center.y + radius * sin(i))});
+		}
+	} else {
+		for (float i = start_angle; i > start_angle - 2 * M_PI; i -= step) {
+			path.push_back(vec2{static_cast<float>(center.x + radius * cos(i)),
+								static_cast<float>(center.y + radius * sin(i))});
+		}
+	}
+}
+
+void AI::make_oval_path(float radius_x, float radius_y, const vec2 & center, float start_angle,
+						bool clockwise, float rotation) {
+	if (radius_x <= 0 && radius_y <= 0) {
+		throw std::runtime_error("Radius must be greater than 0");
+	}
+
+	float max_radius = std::max(radius_x, radius_y);
+	// The step size is determined by the radius (step size is in radians)
+	float step = RADIUS_TO_STEP / max_radius;
+	// Force at least MIN_STEP steps (in case of a small radius)
+	if (step > 2 * M_PI / MIN_STEP) {
+		step = 2 * M_PI / MIN_STEP;
+	}
+	// The path node distance is determined by the step size and the radius
+	this->path_node_distance = max_radius * step * PATH_NODE_DISTANCE_FACTOR;
+
+	std::function<vec2(vec2, vec2)> rotate_point = [rotation](vec2 point, vec2 center) {
+		float s = sin(rotation);
+		float c = cos(rotation);
+
+		// Translate point back to origin
+		point.x -= center.x;
+		point.y -= center.y;
+
+		// Rotate point
+		float xnew = point.x * c - point.y * s;
+		float ynew = point.x * s + point.y * c;
+
+		// Translate point back
+		point.x = xnew + center.x;
+		point.y = ynew + center.y;
+
+		return point;
+	};
+
+	if (clockwise) {
+		for (float i = start_angle; i < 2 * M_PI + start_angle; i += step) {
+			vec2 point = {static_cast<float>(center.x + radius_x * cos(i)),
+						  static_cast<float>(center.y + radius_y * sin(i))};
+			path.push_back(rotate_point(point, center));
+		}
+	} else {
+		for (float i = start_angle; i > start_angle - 2 * M_PI; i -= step) {
+			vec2 point = {static_cast<float>(center.x + radius_x * cos(i)),
+						  static_cast<float>(center.y + radius_y * sin(i))};
+			path.push_back(rotate_point(point, center));
+		}
+	}
+}
+
+} // namespace crepe
diff --git a/src/crepe/api/AI.h b/src/crepe/api/AI.h
new file mode 100644
index 0000000..c780a91
--- /dev/null
+++ b/src/crepe/api/AI.h
@@ -0,0 +1,128 @@
+#pragma once
+
+#include "Component.h"
+#include "types.h"
+
+namespace crepe {
+
+/**
+ * \brief The AI component is used to control the movement of an entity using AI.
+ *
+ * The AI component can be used to control the movement of an entity. The AI component can be used
+ * to implement different behaviors such as seeking, fleeing, arriving, and path following.
+ */
+class AI : public Component {
+public:
+	//! The different types of behaviors that can be used
+	enum BehaviorTypeMask {
+		SEEK = 0x00002,
+		FLEE = 0x00004,
+		ARRIVE = 0x00008,
+		PATH_FOLLOW = 0x00010,
+	};
+
+public:
+	/**
+	 * \param id The id of the game object
+	 * \param max_force The maximum force that can be applied to the entity
+	 */
+	AI(game_object_id_t id, float max_force);
+
+	/**
+	 * \brief Check if a behavior is on (aka activated)
+	 *
+	 * \param behavior The behavior to check
+	 * \return true if the behavior is on, false otherwise
+	 */
+	bool on(BehaviorTypeMask behavior) const { return (flags & behavior); }
+	//! Turn on the seek behavior
+	void seek_on() { flags |= SEEK; }
+	//! Turn off the seek behavior
+	void seek_off() { flags &= ~SEEK; }
+	//! Turn on the flee behavior
+	void flee_on() { flags |= FLEE; }
+	//! Turn off the flee behavior
+	void flee_off() { flags &= ~FLEE; }
+	//! Turn on the arrive behavior
+	void arrive_on() { flags |= ARRIVE; }
+	//! Turn off the arrive behavior
+	void arrive_off() { flags &= ~ARRIVE; }
+	//! Turn on the path follow behavior
+	void path_follow_on() { flags |= PATH_FOLLOW; }
+	//! Turn off the path follow behavior
+	void path_follow_off() { flags &= ~PATH_FOLLOW; }
+
+	/**
+	 * \brief Add a path node (for the path following behavior)
+	 *
+	 * \note The path is not relative to the entity's position (it is an absolute path)
+	 *
+	 * \param node The path node to add
+	 */
+	void add_path_node(const vec2 & node) { path.push_back(node); }
+	/**
+	 * \brief Make a circle path (for the path following behavior)
+	 *
+	 * \note The path is not relative to the entity's position (it is an absolute path)
+	 *
+	 * \param radius The radius of the circle (in game units)
+	 * \param center The center of the circle (in game units)
+	 * \param start_angle The start angle of the circle (in radians)
+	 * \param clockwise The direction of the circle
+	 */
+	void make_circle_path(float radius, const vec2 & center = {0, 0}, float start_angle = 0,
+						  bool clockwise = true);
+	/**
+	 * \brief Make an oval path (for the path following behavior)
+	 *
+	 * \note The path is not relative to the entity's position (it is an absolute path)
+	 *
+	 * \param radius_x The x radius of the oval (in game units)
+	 * \param radius_y The y radius of the oval (in game units)
+	 * \param center The center of the oval (in game units)
+	 * \param start_angle The start angle of the oval (in radians)
+	 * \param clockwise The direction of the oval
+	 * \param rotation The rotation of the oval (in radians)
+	 */
+	void make_oval_path(float radius_x, float radius_y, const vec2 & center = {0, 0},
+						float start_angle = 0, bool clockwise = true, float rotation = 0);
+
+public:
+	//! The maximum force that can be applied to the entity (higher values will make the entity adjust faster)
+	float max_force;
+
+	//! The target to seek at
+	vec2 seek_target;
+	//! The target to arrive at
+	vec2 arrive_target;
+	//! The target to flee from
+	vec2 flee_target;
+	//! The distance at which the entity will start to flee from the target
+	float square_flee_panic_distance = 200.0f * 200.0f;
+	//! The deceleration rate for the arrive behavior (higher values will make the entity decelerate faster (less overshoot))
+	float arrive_deceleration = 40.0f;
+	//! The path to follow (for the path following behavior)
+	std::vector<vec2> path;
+	//! The distance from the path node at which the entity will move to the next node (automatically set by make_circle_path())
+	float path_node_distance = 400.0f;
+	//! Looping behavior for the path
+	bool path_loop = true;
+
+private:
+	//! The flags for the behaviors
+	int flags = 0;
+	//! The current path index
+	size_t path_index = 0;
+
+	//! The AISystem is the only class that should access the flags and path_index variables
+	friend class AISystem;
+
+	//! The minimum amount of steps for the path following behavior
+	static constexpr int MIN_STEP = 16;
+	//! The radius to step size ratio for the path following behavior
+	static constexpr float RADIUS_TO_STEP = 400.0f;
+	//! The path node distance factor for the path following behavior
+	static constexpr float PATH_NODE_DISTANCE_FACTOR = 0.75f;
+};
+
+} // namespace crepe
diff --git a/src/crepe/api/CMakeLists.txt b/src/crepe/api/CMakeLists.txt
index 718e497..46deb67 100644
--- a/src/crepe/api/CMakeLists.txt
+++ b/src/crepe/api/CMakeLists.txt
@@ -22,6 +22,7 @@ target_sources(crepe PUBLIC
 	Script.cpp
 	Button.cpp
 	UIObject.cpp
+	AI.cpp
 )
 
 target_sources(crepe PUBLIC FILE_SET HEADERS FILES
@@ -53,4 +54,5 @@ target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	Asset.h
 	Button.h
 	UIObject.h
+	AI.h
 )
diff --git a/src/crepe/api/LoopManager.cpp b/src/crepe/api/LoopManager.cpp
index 88243c4..1f0ba72 100644
--- a/src/crepe/api/LoopManager.cpp
+++ b/src/crepe/api/LoopManager.cpp
@@ -1,4 +1,6 @@
+#include "../system/AISystem.h"
 #include "../system/AnimatorSystem.h"
+#include "../system/AudioSystem.h"
 #include "../system/CollisionSystem.h"
 #include "../system/InputSystem.h"
 #include "../system/ParticleSystem.h"
@@ -20,6 +22,8 @@ LoopManager::LoopManager() {
 	this->load_system<RenderSystem>();
 	this->load_system<ScriptSystem>();
 	this->load_system<InputSystem>();
+	this->load_system<AudioSystem>();
+	this->load_system<AISystem>();
 }
 
 void LoopManager::process_input() { this->get_system<InputSystem>().update(); }
@@ -35,8 +39,10 @@ void LoopManager::fixed_update() {
 	EventManager & ev = this->mediator.event_manager;
 	ev.dispatch_events();
 	this->get_system<ScriptSystem>().update();
+	this->get_system<AISystem>().update();
 	this->get_system<PhysicsSystem>().update();
 	this->get_system<CollisionSystem>().update();
+	this->get_system<AudioSystem>().update();
 }
 
 void LoopManager::loop() {
diff --git a/src/crepe/api/LoopManager.h b/src/crepe/api/LoopManager.h
index b800f5b..7389124 100644
--- a/src/crepe/api/LoopManager.h
+++ b/src/crepe/api/LoopManager.h
@@ -4,6 +4,8 @@
 
 #include "../facade/SDLContext.h"
 #include "../manager/ComponentManager.h"
+#include "../manager/ResourceManager.h"
+#include "../manager/SaveManager.h"
 #include "../manager/SceneManager.h"
 #include "../system/System.h"
 
@@ -96,6 +98,10 @@ private:
 	ComponentManager component_manager{mediator};
 	//! Scene manager instance
 	SceneManager scene_manager{mediator};
+	//! Resource manager instance
+	ResourceManager resource_manager{mediator};
+	//! Save manager instance
+	SaveManager save_manager{mediator};
 
 	SDLContext sdl_context {mediator};
 
diff --git a/src/crepe/api/Script.cpp b/src/crepe/api/Script.cpp
index 4091fd4..753a9e3 100644
--- a/src/crepe/api/Script.cpp
+++ b/src/crepe/api/Script.cpp
@@ -8,8 +8,7 @@ using namespace crepe;
 using namespace std;
 
 Script::~Script() {
-	Mediator & mediator = this->mediator;
-	EventManager & mgr = mediator.event_manager;
+	EventManager & mgr = this->mediator->event_manager;
 	for (auto id : this->listeners) {
 		mgr.unsubscribe(id);
 	}
@@ -21,7 +20,8 @@ void Script::subscribe(const EventHandler<CollisionEvent> & callback) {
 }
 
 void Script::set_next_scene(const string & name) {
-	Mediator & mediator = this->mediator;
-	SceneManager & mgr = mediator.scene_manager;
+	SceneManager & mgr = this->mediator->scene_manager;
 	mgr.set_next_scene(name);
 }
+
+SaveManager & Script::get_save_manager() const { return this->mediator->save_manager; }
diff --git a/src/crepe/api/Script.h b/src/crepe/api/Script.h
index d99ab0e..668e5d1 100644
--- a/src/crepe/api/Script.h
+++ b/src/crepe/api/Script.h
@@ -86,6 +86,25 @@ protected:
 	RefVector<T> get_components() const;
 
 	/**
+	 * \copydoc ComponentManager::get_components_by_id
+	 * \see ComponentManager::get_components_by_id
+	 */
+	template <typename T>
+	RefVector<T> get_components_by_id(game_object_id_t id) const;
+	/**
+	 * \copydoc ComponentManager::get_components_by_name
+	 * \see ComponentManager::get_components_by_name
+	 */
+	template <typename T>
+	RefVector<T> get_components_by_name(const std::string & name) const;
+	/**
+	 * \copydoc ComponentManager::get_components_by_tag
+	 * \see ComponentManager::get_components_by_tag
+	 */
+	template <typename T>
+	RefVector<T> get_components_by_tag(const std::string & tag) const;
+
+	/**
 	 * \brief Log a message using Log::logf
 	 *
 	 * \tparam Args Log::logf parameters
@@ -113,6 +132,9 @@ protected:
 	 */
 	void set_next_scene(const std::string & name);
 
+	//! Retrieve SaveManager reference
+	SaveManager & get_save_manager() const;
+
 	//! \}
 
 private:
diff --git a/src/crepe/api/Script.hpp b/src/crepe/api/Script.hpp
index 45f1ff1..225a51c 100644
--- a/src/crepe/api/Script.hpp
+++ b/src/crepe/api/Script.hpp
@@ -20,10 +20,7 @@ T & Script::get_component() const {
 
 template <typename T>
 RefVector<T> Script::get_components() const {
-	Mediator & mediator = this->mediator;
-	ComponentManager & mgr = mediator.component_manager;
-
-	return mgr.get_components_by_id<T>(this->game_object_id);
+	return this->get_components_by_id<T>(this->game_object_id);
 }
 
 template <typename... Args>
@@ -34,8 +31,7 @@ void Script::logf(Args &&... args) {
 template <typename EventType>
 void Script::subscribe_internal(const EventHandler<EventType> & callback,
 								event_channel_t channel) {
-	Mediator & mediator = this->mediator;
-	EventManager & mgr = mediator.event_manager;
+	EventManager & mgr = this->mediator->event_manager;
 	subscription_t listener = mgr.subscribe<EventType>(
 		[this, callback](const EventType & data) -> bool {
 			bool & active = this->active;
@@ -56,4 +52,26 @@ void Script::subscribe(const EventHandler<EventType> & callback) {
 	this->subscribe_internal(callback, EventManager::CHANNEL_ALL);
 }
 
+template <typename T>
+RefVector<T> Script::get_components_by_id(game_object_id_t id) const {
+	Mediator & mediator = this->mediator;
+	ComponentManager & mgr = mediator.component_manager;
+
+	return mgr.get_components_by_id<T>(id);
+}
+template <typename T>
+RefVector<T> Script::get_components_by_name(const std::string & name) const {
+	Mediator & mediator = this->mediator;
+	ComponentManager & mgr = mediator.component_manager;
+
+	return mgr.get_components_by_name<T>(name);
+}
+template <typename T>
+RefVector<T> Script::get_components_by_tag(const std::string & tag) const {
+	Mediator & mediator = this->mediator;
+	ComponentManager & mgr = mediator.component_manager;
+
+	return mgr.get_components_by_tag<T>(tag);
+}
+
 } // namespace crepe
diff --git a/src/crepe/api/Vector2.h b/src/crepe/api/Vector2.h
index c278c87..bf9d124 100644
--- a/src/crepe/api/Vector2.h
+++ b/src/crepe/api/Vector2.h
@@ -66,6 +66,30 @@ struct Vector2 {
 
 	//! Checks if this vector is not equal to another vector.
 	bool operator!=(const Vector2<T> & other) const;
+
+	//! Truncates the vector to a maximum length.
+	void truncate(T max);
+
+	//! Normalizes the vector (resulting in vector with a length of 1).
+	void normalize();
+
+	//! Returns the length of the vector.
+	T length() const;
+
+	//! Returns the squared length of the vector.
+	T length_squared() const;
+
+	//! Returns the dot product (inwendig product) of this vector and another vector.
+	T dot(const Vector2<T> & other) const;
+
+	//! Returns the distance between this vector and another vector.
+	T distance(const Vector2<T> & other) const;
+
+	//! Returns the squared distance between this vector and another vector.
+	T distance_squared(const Vector2<T> & other) const;
+
+	//! Returns the perpendicular vector to this vector.
+	Vector2 perpendicular() const;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Vector2.hpp b/src/crepe/api/Vector2.hpp
index cad15f8..ff53cb0 100644
--- a/src/crepe/api/Vector2.hpp
+++ b/src/crepe/api/Vector2.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <cmath>
+
 #include "Vector2.h"
 
 namespace crepe {
@@ -115,4 +117,50 @@ bool Vector2<T>::operator!=(const Vector2<T> & other) const {
 	return !(*this == other);
 }
 
+template <class T>
+void Vector2<T>::truncate(T max) {
+	if (length() > max) {
+		normalize();
+		*this *= max;
+	}
+}
+
+template <class T>
+void Vector2<T>::normalize() {
+	T len = length();
+	if (len > 0) {
+		*this /= len;
+	}
+}
+
+template <class T>
+T Vector2<T>::length() const {
+	return std::sqrt(x * x + y * y);
+}
+
+template <class T>
+T Vector2<T>::length_squared() const {
+	return x * x + y * y;
+}
+
+template <class T>
+T Vector2<T>::dot(const Vector2<T> & other) const {
+	return x * other.x + y * other.y;
+}
+
+template <class T>
+T Vector2<T>::distance(const Vector2<T> & other) const {
+	return (*this - other).length();
+}
+
+template <class T>
+T Vector2<T>::distance_squared(const Vector2<T> & other) const {
+	return (*this - other).length_squared();
+}
+
+template <class T>
+Vector2<T> Vector2<T>::perpendicular() const {
+	return {-y, x};
+}
+
 } // namespace crepe
diff --git a/src/crepe/facade/SDLContext.cpp b/src/crepe/facade/SDLContext.cpp
index a92ec8b..a0d7f04 100644
--- a/src/crepe/facade/SDLContext.cpp
+++ b/src/crepe/facade/SDLContext.cpp
@@ -233,7 +233,7 @@ SDL_FRect SDLContext::get_dst_rect(const DestinationRectangleData & ctx) const {
 
 	const Sprite::Data & data = ctx.sprite.data;
 
-	vec2 size = {data.size.x, data.size.y};
+	vec2 size = data.size;
 	if (data.size.x == 0 && data.size.y != 0) {
 		size.x = data.size.y * ctx.texture.get_ratio();
 	}
diff --git a/src/crepe/manager/ComponentManager.cpp b/src/crepe/manager/ComponentManager.cpp
index 80cf8b4..df30d27 100644
--- a/src/crepe/manager/ComponentManager.cpp
+++ b/src/crepe/manager/ComponentManager.cpp
@@ -1,4 +1,5 @@
 #include "../api/GameObject.h"
+#include "../api/Metadata.h"
 #include "../types.h"
 #include "../util/Log.h"
 
@@ -61,3 +62,13 @@ GameObject ComponentManager::new_object(const string & name, const string & tag,
 void ComponentManager::set_persistent(game_object_id_t id, bool persistent) {
 	this->persistent[id] = persistent;
 }
+
+set<game_object_id_t> ComponentManager::get_objects_by_name(const string & name) const {
+	return this->get_objects_by_predicate<Metadata>(
+		[name](const Metadata & data) { return data.name == name; });
+}
+
+set<game_object_id_t> ComponentManager::get_objects_by_tag(const string & tag) const {
+	return this->get_objects_by_predicate<Metadata>(
+		[tag](const Metadata & data) { return data.tag == tag; });
+}
diff --git a/src/crepe/manager/ComponentManager.h b/src/crepe/manager/ComponentManager.h
index 44429d9..19a8e81 100644
--- a/src/crepe/manager/ComponentManager.h
+++ b/src/crepe/manager/ComponentManager.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <memory>
+#include <set>
 #include <typeindex>
 #include <unordered_map>
 #include <vector>
@@ -134,8 +135,77 @@ public:
 	 */
 	template <typename T>
 	RefVector<T> get_components_by_type() const;
+	/**
+	 * \brief Get all components of a specific type on a GameObject with name \c name
+	 * 
+	 * \tparam T The type of the component
+	 * \param name Metadata::name for the same game_object_id as the returned components
+	 * \return Components matching criteria
+	 */
+	template <typename T>
+	RefVector<T> get_components_by_name(const std::string & name) const;
+	/**
+	 * \brief Get all components of a specific type on a GameObject with tag \c tag
+	 * 
+	 * \tparam T The type of the component
+	 * \param name Metadata::tag for the same game_object_id as the returned components
+	 * \return Components matching criteria
+	 */
+	template <typename T>
+	RefVector<T> get_components_by_tag(const std::string & tag) const;
+
+private:
+	/**
+	 * \brief Get object IDs by predicate function
+	 *
+	 * This function calls the predicate function \c pred for all components matching type \c T,
+	 * and adds their parent game_object_id to a \c std::set if the predicate returns true.
+	 *
+	 * \tparam T The type of the component to check the predicate against
+	 * \param pred Predicate function
+	 *
+	 * \note The predicate function may be called for multiple components with the same \c
+	 * game_object_id. In this case, the ID is added if *any* call returns \c true.
+	 *
+	 * \returns game_object_id for all components where the predicate returned true
+	 */
+	template <typename T>
+	std::set<game_object_id_t>
+	get_objects_by_predicate(const std::function<bool(const T &)> & pred) const;
+
+	/**
+	 * \brief Get components of type \c T for multiple game object IDs
+	 *
+	 * \tparam T The type of the components to return
+	 * \param ids The object IDs
+	 *
+	 * \return All components matching type \c T and one of the IDs in \c ids
+	 */
+	template <typename T>
+	RefVector<T> get_components_by_ids(const std::set<game_object_id_t> & ids) const;
+
+	/**
+	 * \brief Get object IDs for objects with name \c name
+	 *
+	 * \param name Object name to match
+	 * \returns Object IDs where Metadata::name is equal to \c name
+	 */
+	std::set<game_object_id_t> get_objects_by_name(const std::string & name) const;
+	/**
+	 * \brief Get object IDs for objects with tag \c tag
+	 *
+	 * \param tag Object tag to match
+	 * \returns Object IDs where Metadata::tag is equal to \c tag
+	 */
+	std::set<game_object_id_t> get_objects_by_tag(const std::string & tag) const;
 
 private:
+	//! By Component \c std::type_index (readability helper type)
+	template <typename T>
+	using by_type = std::unordered_map<std::type_index, T>;
+	//! By \c game_object_id index (readability helper type)
+	template <typename T>
+	using by_id_index = std::vector<T>;
 	/**
 	 * \brief The components
 	 *
@@ -146,8 +216,7 @@ private:
 	 * The first vector is for the ids of the GameObjects and the second vector is for the
 	 * components (because a GameObject might have multiple components).
 	 */
-	std::unordered_map<std::type_index, std::vector<std::vector<std::unique_ptr<Component>>>>
-		components;
+	by_type<by_id_index<std::vector<std::unique_ptr<Component>>>> components;
 
 	//! Persistent flag for each GameObject
 	std::unordered_map<game_object_id_t, bool> persistent;
diff --git a/src/crepe/manager/ComponentManager.hpp b/src/crepe/manager/ComponentManager.hpp
index ffb38ec..9e70865 100644
--- a/src/crepe/manager/ComponentManager.hpp
+++ b/src/crepe/manager/ComponentManager.hpp
@@ -95,32 +95,25 @@ template <typename T>
 RefVector<T> ComponentManager::get_components_by_id(game_object_id_t id) const {
 	using namespace std;
 
-	// Determine the type of T (this is used as the key of the unordered_map<>)
-	type_index type = typeid(T);
-
-	// Create an empty vector<>
-	RefVector<T> component_vector;
-
-	if (this->components.find(type) == this->components.end()) return component_vector;
-
-	// Get the correct vector<>
-	const vector<vector<unique_ptr<Component>>> & component_array = this->components.at(type);
-
-	// Make sure that the id (that we are looking for) is within the boundaries of the vector<>
-	if (id >= component_array.size()) return component_vector;
-
-	// Loop trough the whole vector<>
-	for (const unique_ptr<Component> & component_ptr : component_array[id]) {
-		// Cast the unique_ptr to a raw pointer
-		T * casted_component = static_cast<T *>(component_ptr.get());
-
-		if (casted_component == nullptr) continue;
+	static_assert(is_base_of<Component, T>::value,
+				  "get_components_by_id must recieve a derivative class of Component");
 
-		// Add the dereferenced raw pointer to the vector<>
-		component_vector.push_back(*casted_component);
+	type_index type = typeid(T);
+	if (!this->components.contains(type)) return {};
+
+	const by_id_index<vector<unique_ptr<Component>>> & components_by_id
+		= this->components.at(type);
+	if (id >= components_by_id.size()) return {};
+
+	RefVector<T> out = {};
+	const vector<unique_ptr<Component>> & components = components_by_id.at(id);
+	for (auto & component_ptr : components) {
+		if (component_ptr == nullptr) continue;
+		Component & component = *component_ptr.get();
+		out.push_back(static_cast<T &>(component));
 	}
 
-	return component_vector;
+	return out;
 }
 
 template <typename T>
@@ -158,4 +151,46 @@ RefVector<T> ComponentManager::get_components_by_type() const {
 	return component_vector;
 }
 
+template <typename T>
+std::set<game_object_id_t>
+ComponentManager::get_objects_by_predicate(const std::function<bool(const T &)> & pred) const {
+	using namespace std;
+
+	set<game_object_id_t> objects = {};
+	RefVector<T> components = this->get_components_by_type<T>();
+
+	for (const T & component : components) {
+		game_object_id_t id = dynamic_cast<const Component &>(component).game_object_id;
+		if (objects.contains(id)) continue;
+		if (!pred(component)) continue;
+		objects.insert(id);
+	}
+
+	return objects;
+}
+
+template <typename T>
+RefVector<T>
+ComponentManager::get_components_by_ids(const std::set<game_object_id_t> & ids) const {
+	using namespace std;
+
+	RefVector<T> out = {};
+	for (game_object_id_t id : ids) {
+		RefVector<T> components = get_components_by_id<T>(id);
+		out.insert(out.end(), components.begin(), components.end());
+	}
+
+	return out;
+}
+
+template <typename T>
+RefVector<T> ComponentManager::get_components_by_name(const std::string & name) const {
+	return this->get_components_by_ids<T>(this->get_objects_by_name(name));
+}
+
+template <typename T>
+RefVector<T> ComponentManager::get_components_by_tag(const std::string & tag) const {
+	return this->get_components_by_ids<T>(this->get_objects_by_tag(tag));
+}
+
 } // namespace crepe
diff --git a/src/crepe/manager/Mediator.h b/src/crepe/manager/Mediator.h
index bb51d6b..d5f7e00 100644
--- a/src/crepe/manager/Mediator.h
+++ b/src/crepe/manager/Mediator.h
@@ -5,11 +5,13 @@
 // TODO: remove these singletons:
 #include "EventManager.h"
 #include "SaveManager.h"
+#include "api/LoopTimer.h"
 
 namespace crepe {
 
 class ComponentManager;
 class SceneManager;
+class SaveManager;
 class ResourceManager;
 class SDLContext;
 class LoopTimer;
@@ -30,7 +32,7 @@ struct Mediator {
 	OptionalRef<SDLContext> sdl_context;
 	OptionalRef<ComponentManager> component_manager;
 	OptionalRef<SceneManager> scene_manager;
-	OptionalRef<SaveManager> save_manager = SaveManager::get_instance();
+	OptionalRef<SaveManager> save_manager;
 	OptionalRef<EventManager> event_manager = EventManager::get_instance();
 	OptionalRef<ResourceManager> resource_manager;
 	OptionalRef<LoopTimer> timer;
diff --git a/src/crepe/manager/SaveManager.cpp b/src/crepe/manager/SaveManager.cpp
index d4ed1c1..691ea2f 100644
--- a/src/crepe/manager/SaveManager.cpp
+++ b/src/crepe/manager/SaveManager.cpp
@@ -1,13 +1,25 @@
 #include "../ValueBroker.h"
 #include "../api/Config.h"
 #include "../facade/DB.h"
-#include "../util/Log.h"
 
 #include "SaveManager.h"
 
 using namespace std;
 using namespace crepe;
 
+SaveManager::SaveManager(Mediator & mediator) : Manager(mediator) {
+	mediator.save_manager = *this;
+}
+
+DB & SaveManager::get_db() {
+	if (this->db == nullptr) {
+		Config & cfg = Config::get_instance();
+		this->db
+			= {new DB(cfg.savemgr.location), [](void * db) { delete static_cast<DB *>(db); }};
+	}
+	return *static_cast<DB *>(this->db.get());
+}
+
 template <>
 string SaveManager::serialize(const string & value) const noexcept {
 	return value;
@@ -90,22 +102,6 @@ int32_t SaveManager::deserialize(const string & value) const noexcept {
 	return deserialize<int64_t>(value);
 }
 
-SaveManager::SaveManager() { dbg_trace(); }
-
-SaveManager & SaveManager::get_instance() {
-	dbg_trace();
-	static SaveManager instance;
-	return instance;
-}
-
-DB & SaveManager::get_db() {
-	Config & cfg = Config::get_instance();
-	// TODO: make this path relative to XDG_DATA_HOME on Linux and whatever the
-	// default equivalent is on Windows using some third party library
-	static DB db(cfg.savemgr.location);
-	return db;
-}
-
 bool SaveManager::has(const string & key) {
 	DB & db = this->get_db();
 	return db.has(key);
@@ -155,7 +151,8 @@ ValueBroker<T> SaveManager::get(const string & key) {
 	return {
 		[this, key](const T & target) { this->set<T>(key, target); },
 		[this, key, value]() mutable -> const T & {
-			value = this->deserialize<T>(this->get_db().get(key));
+			DB & db = this->get_db();
+			value = this->deserialize<T>(db.get(key));
 			return value;
 		},
 	};
diff --git a/src/crepe/manager/SaveManager.h b/src/crepe/manager/SaveManager.h
index 3d8c852..61a978d 100644
--- a/src/crepe/manager/SaveManager.h
+++ b/src/crepe/manager/SaveManager.h
@@ -1,9 +1,12 @@
 #pragma once
 
+#include <functional>
 #include <memory>
 
 #include "../ValueBroker.h"
 
+#include "Manager.h"
+
 namespace crepe {
 
 class DB;
@@ -18,7 +21,7 @@ class DB;
  *
  * The underlying database is a key-value store.
  */
-class SaveManager {
+class SaveManager : public Manager {
 public:
 	/**
 	 * \brief Get a read/write reference to a value and initialize it if it does not yet exist
@@ -63,8 +66,8 @@ public:
 	 */
 	bool has(const std::string & key);
 
-private:
-	SaveManager();
+public:
+	SaveManager(Mediator & mediator);
 	virtual ~SaveManager() = default;
 
 private:
@@ -89,26 +92,13 @@ private:
 	template <typename T>
 	T deserialize(const std::string & value) const noexcept;
 
-public:
-	// singleton
-	static SaveManager & get_instance();
-	SaveManager(const SaveManager &) = delete;
-	SaveManager(SaveManager &&) = delete;
-	SaveManager & operator=(const SaveManager &) = delete;
-	SaveManager & operator=(SaveManager &&) = delete;
+protected:
+	//! Create or return DB
+	virtual DB & get_db();
 
 private:
-	/**
-	 * \brief Create an instance of DB and return its reference
-	 *
-	 * \returns DB instance
-	 *
-	 * This function exists because DB is a facade class, which can't directly be used in the API
-	 * without workarounds
-	 *
-	 * TODO: better solution
-	 */
-	static DB & get_db();
+	//! Database
+	std::unique_ptr<void, std::function<void(void *)>> db = nullptr;
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/AISystem.cpp b/src/crepe/system/AISystem.cpp
new file mode 100644
index 0000000..e2e36a5
--- /dev/null
+++ b/src/crepe/system/AISystem.cpp
@@ -0,0 +1,185 @@
+#include <algorithm>
+#include <cmath>
+
+#include "api/LoopTimer.h"
+#include "manager/ComponentManager.h"
+#include "manager/Mediator.h"
+
+#include "AISystem.h"
+
+using namespace crepe;
+
+void AISystem::update() {
+	const Mediator & mediator = this->mediator;
+	ComponentManager & mgr = mediator.component_manager;
+	RefVector<AI> ai_components = mgr.get_components_by_type<AI>();
+
+	//TODO: Use fixed loop dt (this is not available at master at the moment)
+	double dt = LoopTimer::get_instance().get_delta_time();
+
+	// Loop through all AI components
+	for (AI & ai : ai_components) {
+		if (!ai.active) {
+			continue;
+		}
+
+		RefVector<Rigidbody> rigidbodies
+			= mgr.get_components_by_id<Rigidbody>(ai.game_object_id);
+		if (rigidbodies.empty()) {
+			throw std::runtime_error(
+				"AI component must be attached to a GameObject with a Rigidbody component");
+		}
+		Rigidbody & rigidbody = rigidbodies.front().get();
+		if (!rigidbody.active) {
+			continue;
+		}
+		if (rigidbody.data.mass <= 0) {
+			throw std::runtime_error("Mass must be greater than 0");
+		}
+
+		// Calculate the force to apply to the entity
+		vec2 force = this->calculate(ai, rigidbody);
+		// Calculate the acceleration (using the above calculated force)
+		vec2 acceleration = force / rigidbody.data.mass;
+		// Finally, update Rigidbody's velocity
+		rigidbody.data.linear_velocity += acceleration * dt;
+	}
+}
+
+vec2 AISystem::calculate(AI & ai, const Rigidbody & rigidbody) {
+	const Mediator & mediator = this->mediator;
+	ComponentManager & mgr = mediator.component_manager;
+	RefVector<Transform> transforms = mgr.get_components_by_id<Transform>(ai.game_object_id);
+	Transform & transform = transforms.front().get();
+
+	vec2 force;
+
+	// Run all the behaviors that are on, and stop if the force gets too high
+	if (ai.on(AI::BehaviorTypeMask::FLEE)) {
+		vec2 force_to_add = this->flee(ai, rigidbody, transform);
+
+		if (!this->accumulate_force(ai, force, force_to_add)) {
+			return force;
+		}
+	}
+	if (ai.on(AI::BehaviorTypeMask::ARRIVE)) {
+		vec2 force_to_add = this->arrive(ai, rigidbody, transform);
+
+		if (!this->accumulate_force(ai, force, force_to_add)) {
+			return force;
+		}
+	}
+	if (ai.on(AI::BehaviorTypeMask::SEEK)) {
+		vec2 force_to_add = this->seek(ai, rigidbody, transform);
+
+		if (!this->accumulate_force(ai, force, force_to_add)) {
+			return force;
+		}
+	}
+	if (ai.on(AI::BehaviorTypeMask::PATH_FOLLOW)) {
+		vec2 force_to_add = this->path_follow(ai, rigidbody, transform);
+
+		if (!this->accumulate_force(ai, force, force_to_add)) {
+			return force;
+		}
+	}
+
+	return force;
+}
+
+bool AISystem::accumulate_force(const AI & ai, vec2 & running_total, vec2 & force_to_add) {
+	float magnitude = running_total.length();
+	float magnitude_remaining = ai.max_force - magnitude;
+
+	if (magnitude_remaining <= 0.0f) {
+		// If the force is already at/above the max force, return false
+		return false;
+	}
+
+	float magnitude_to_add = force_to_add.length();
+	if (magnitude_to_add < magnitude_remaining) {
+		// If the force to add is less than the remaining force, add it
+		running_total += force_to_add;
+	} else {
+		// If the force to add is greater than the remaining force, add a fraction of it
+		force_to_add.normalize();
+		running_total += force_to_add * magnitude_remaining;
+	}
+
+	return true;
+}
+
+vec2 AISystem::seek(const AI & ai, const Rigidbody & rigidbody,
+					const Transform & transform) const {
+	// Calculate the desired velocity
+	vec2 desired_velocity = ai.seek_target - transform.position;
+	desired_velocity.normalize();
+	desired_velocity *= rigidbody.data.max_linear_velocity;
+
+	return desired_velocity - rigidbody.data.linear_velocity;
+}
+
+vec2 AISystem::flee(const AI & ai, const Rigidbody & rigidbody,
+					const Transform & transform) const {
+	// Calculate the desired velocity if the entity is within the panic distance
+	vec2 desired_velocity = transform.position - ai.flee_target;
+	if (desired_velocity.length_squared() > ai.square_flee_panic_distance) {
+		return vec2{0, 0};
+	}
+	desired_velocity.normalize();
+	desired_velocity *= rigidbody.data.max_linear_velocity;
+
+	return desired_velocity - rigidbody.data.linear_velocity;
+}
+
+vec2 AISystem::arrive(const AI & ai, const Rigidbody & rigidbody,
+					  const Transform & transform) const {
+	// Calculate the desired velocity (taking into account the deceleration rate)
+	vec2 to_target = ai.arrive_target - transform.position;
+	float distance = to_target.length();
+	if (distance > 0.0f) {
+		if (ai.arrive_deceleration <= 0.0f) {
+			throw std::runtime_error("Deceleration rate must be greater than 0");
+		}
+
+		float speed = distance / ai.arrive_deceleration;
+		speed = std::min(speed, rigidbody.data.max_linear_velocity.length());
+		vec2 desired_velocity = to_target * (speed / distance);
+
+		return desired_velocity - rigidbody.data.linear_velocity;
+	}
+
+	return vec2{0, 0};
+}
+
+vec2 AISystem::path_follow(AI & ai, const Rigidbody & rigidbody, const Transform & transform) {
+	if (ai.path.empty()) {
+		return vec2{0, 0};
+	}
+
+	// Get the target node
+	vec2 target = ai.path.at(ai.path_index);
+	// Calculate the force to apply to the entity
+	vec2 to_target = target - transform.position;
+	if (to_target.length_squared() > ai.path_node_distance * ai.path_node_distance) {
+		// If the entity is not close enough to the target node, seek it
+		ai.seek_target = target;
+		ai.arrive_target = target;
+	} else {
+		// If the entity is close enough to the target node, move to the next node
+		ai.path_index++;
+		if (ai.path_index >= ai.path.size()) {
+			if (ai.path_loop) {
+				// If the path is looping, reset the path index
+				ai.path_index = 0;
+			} else {
+				// If the path is not looping, arrive at the last node
+				ai.path_index = ai.path.size() - 1;
+				return this->arrive(ai, rigidbody, transform);
+			}
+		}
+	}
+
+	// Seek the target node
+	return this->seek(ai, rigidbody, transform);
+}
diff --git a/src/crepe/system/AISystem.h b/src/crepe/system/AISystem.h
new file mode 100644
index 0000000..d5f8a8e
--- /dev/null
+++ b/src/crepe/system/AISystem.h
@@ -0,0 +1,81 @@
+#pragma once
+
+#include "api/AI.h"
+#include "api/Rigidbody.h"
+
+#include "System.h"
+#include "api/Transform.h"
+#include "types.h"
+
+namespace crepe {
+
+/**
+ * \brief The AISystem is used to control the movement of entities using AI.
+ *
+ * The AISystem is used to control the movement of entities using AI. The AISystem can be used to
+ * implement different behaviors such as seeking, fleeing, arriving, and path following.
+ */
+class AISystem : public System {
+public:
+	using System::System;
+
+	//! Update the AI system
+	void update() override;
+
+private:
+	/**
+	 * \brief Calculate the total force to apply to the entity
+	 *
+	 * \param ai The AI component
+	 * \param rigidbody The Rigidbody component
+	 */
+	vec2 calculate(AI & ai, const Rigidbody & rigidbody);
+	/**
+	 * \brief Accumulate the force to apply to the entity
+	 *
+	 * \param ai The AI component
+	 * \param running_total The running total of the force
+	 * \param force_to_add The force to add
+	 * \return true if the force was added, false otherwise
+	 */
+	bool accumulate_force(const AI & ai, vec2 & running_total, vec2 & force_to_add);
+
+	/**
+	 * \brief Calculate the seek force
+	 *
+	 * \param ai The AI component
+	 * \param rigidbody The Rigidbody component
+	 * \param transform The Transform component
+	 * \return The seek force
+	 */
+	vec2 seek(const AI & ai, const Rigidbody & rigidbody, const Transform & transform) const;
+	/**
+	 * \brief Calculate the flee force
+	 *
+	 * \param ai The AI component
+	 * \param rigidbody The Rigidbody component
+	 * \param transform The Transform component
+	 * \return The flee force
+	 */
+	vec2 flee(const AI & ai, const Rigidbody & rigidbody, const Transform & transform) const;
+	/**
+	 * \brief Calculate the arrive force
+	 *
+	 * \param ai The AI component
+	 * \param rigidbody The Rigidbody component
+	 * \param transform The Transform component
+	 * \return The arrive force
+	 */
+	vec2 arrive(const AI & ai, const Rigidbody & rigidbody, const Transform & transform) const;
+	/**
+	 * \brief Calculate the path follow force
+	 *
+	 * \param ai The AI component
+	 * \param rigidbody The Rigidbody component
+	 * \param transform The Transform component
+	 * \return The path follow force
+	 */
+	vec2 path_follow(AI & ai, const Rigidbody & rigidbody, const Transform & transform);
+};
+
+} // namespace crepe
diff --git a/src/crepe/system/AudioSystem.cpp b/src/crepe/system/AudioSystem.cpp
index b2c1dc6..b1aa0f8 100644
--- a/src/crepe/system/AudioSystem.cpp
+++ b/src/crepe/system/AudioSystem.cpp
@@ -26,12 +26,11 @@ void AudioSystem::diff_update(AudioSource & component, Sound & resource) {
 	SoundContext & context = this->get_context();
 
 	if (component.active != component.last_active) {
-		if (component.active) {
-			component.oneshot_play = component.play_on_awake;
-		} else {
+		if (!component.active) {
 			context.stop(component.voice);
 			return;
 		}
+		if (component.play_on_awake) component.oneshot_play = true;
 	}
 	if (!component.active) return;
 
diff --git a/src/crepe/system/CMakeLists.txt b/src/crepe/system/CMakeLists.txt
index 6b2e099..0e2db76 100644
--- a/src/crepe/system/CMakeLists.txt
+++ b/src/crepe/system/CMakeLists.txt
@@ -8,6 +8,7 @@ target_sources(crepe PUBLIC
 	AudioSystem.cpp
 	AnimatorSystem.cpp
 	InputSystem.cpp
+	AISystem.cpp
 )
 
 target_sources(crepe PUBLIC FILE_SET HEADERS FILES
@@ -19,4 +20,5 @@ target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	AudioSystem.h
 	AnimatorSystem.h
 	InputSystem.h
+	AISystem.h
 )
diff --git a/src/crepe/util/OptionalRef.h b/src/crepe/util/OptionalRef.h
index 3201667..1b2cb3f 100644
--- a/src/crepe/util/OptionalRef.h
+++ b/src/crepe/util/OptionalRef.h
@@ -25,7 +25,7 @@ public:
 	 */
 	OptionalRef<T> & operator=(T & ref);
 	/**
-	 * \brief Retrieve this reference
+	 * \brief Retrieve this reference (cast)
 	 *
 	 * \returns Internal reference if it is set
 	 *
@@ -33,6 +33,14 @@ public:
 	 */
 	operator T &() const;
 	/**
+	 * \brief Retrieve this reference (member access)
+	 *
+	 * \returns Internal reference if it is set
+	 *
+	 * \throws std::runtime_error if this function is called while the reference it not set
+	 */
+	T * operator->() const;
+	/**
 	 * \brief Check if this reference is not empty
 	 *
 	 * \returns `true` if reference is set, or `false` if it is not
diff --git a/src/crepe/util/OptionalRef.hpp b/src/crepe/util/OptionalRef.hpp
index 4608c9e..5e36b3a 100644
--- a/src/crepe/util/OptionalRef.hpp
+++ b/src/crepe/util/OptionalRef.hpp
@@ -19,6 +19,13 @@ OptionalRef<T>::operator T &() const {
 }
 
 template <typename T>
+T * OptionalRef<T>::operator->() const {
+	if (this->ref == nullptr)
+		throw std::runtime_error("OptionalRef: attempt to dereference nullptr");
+	return this->ref;
+}
+
+template <typename T>
 OptionalRef<T> & OptionalRef<T>::operator=(T & ref) {
 	this->ref = &ref;
 	return *this;