Proposal for observers and deferred implementations (#1599)

dCommon/Implementation.h

@@ -0,0 +1,92 @@
+#ifndef __IMPLEMENTATION_H__
+#define __IMPLEMENTATION_H__
+
+#include <functional>
+#include <optional>
+
+/**
+ * @brief A way to defer the implementation of an action.
+ * 
+ * @tparam R The result of the action.
+ * @tparam T The types of the arguments that the implementation requires.
+ */
+template <typename R, typename... T>
+class Implementation {
+public:
+	typedef std::function<std::optional<R>(T...)> ImplementationFunction;
+
+	/**
+	 * @brief Sets the implementation of the action.
+	 * 
+	 * @param implementation The implementation of the action.
+	 */
+	void SetImplementation(const ImplementationFunction& implementation) {
+		this->implementation = implementation;
+	}
+
+	/**
+	 * @brief Clears the implementation of the action.
+	 */
+	void ClearImplementation() {
+		implementation.reset();
+	}
+
+	/**
+	 * @brief Checks if the implementation is set.
+	 * 
+	 * @return true If the implementation is set.
+	 * @return false If the implementation is not set.
+	 */
+	bool IsSet() const {
+		return implementation.has_value();
+	}
+
+	/**
+	 * @brief Executes the implementation if it is set.
+	 * 
+	 * @param args The arguments to pass to the implementation.
+	 * @return std::optional<R> The optional result of the implementation. If the result is not set, it indicates that the default action should be taken.
+	 */
+	std::optional<R> Execute(T... args) const {
+		return IsSet() ? implementation.value()(args...) : std::nullopt;
+	}
+
+	/**
+	 * @brief Exectues the implementation if it is set, otherwise returns a default value.
+	 * 
+	 * @param args The arguments to pass to the implementation.
+	 * @param defaultValue The default value to return if the implementation is not set or should not be deferred.
+	 */
+	R ExecuteWithDefault(T... args, const R& defaultValue) const {
+		return Execute(args...).value_or(defaultValue);
+	}
+
+	/**
+	 * = operator overload.
+	 */
+	Implementation& operator=(const Implementation& other) {
+		implementation = other.implementation;
+		return *this;
+	}
+
+	/**
+	 * = operator overload.
+	 */
+	Implementation& operator=(const ImplementationFunction& implementation) {
+		this->implementation = implementation;
+		return *this;
+	}
+
+	/**
+	 * () operator overload.
+	 */
+	std::optional<R> operator()(T... args) {
+		return !IsSet() ? std::nullopt : implementation(args...);
+	}
+
+private:
+	std::optional<ImplementationFunction> implementation;
+
+};
+
+#endif  //!__IMPLEMENTATION_H__

dCommon/Observable.h

@@ -0,0 +1,73 @@
+#ifndef __OBSERVABLE_H__
+#define __OBSERVABLE_H__
+
+#include <vector>
+#include <functional>
+
+/**
+ * @brief An event which can be observed by multiple observers.
+ * 
+ * @tparam T The types of the arguments to be passed to the observers.
+ */
+template <typename... T>
+class Observable {
+public:
+	typedef std::function<void(T...)> Observer;
+
+	/**
+	 * @brief Adds an observer to the event.
+	 * 
+	 * @param observer The observer to add.
+	 */
+	void AddObserver(const Observer& observer) {
+		observers.push_back(observer);
+	}
+
+	/**
+	 * @brief Removes an observer from the event.
+	 * 
+	 * @param observer The observer to remove.
+	 */
+	void RemoveObserver(const Observer& observer) {
+		observers.erase(std::remove(observers.begin(), observers.end(), observer), observers.end());
+	}
+
+	/**
+	 * @brief Notifies all observers of the event.
+	 * 
+	 * @param args The arguments to pass to the observers.
+	 */
+	void Notify(T... args) {
+		for (const auto& observer : observers) {
+			observer(args...);
+		}
+	}
+
+	/**
+	 * += operator overload.
+	 */
+	Observable& operator+=(const Observer& observer) {
+		AddObserver(observer);
+		return *this;
+	}
+
+	/**
+	 * -= operator overload.
+	 */
+	Observable& operator-=(const Observer& observer) {
+		RemoveObserver(observer);
+		return *this;
+	}
+
+	/**
+	 * () operator overload.
+	 */
+	void operator()(T... args) {
+		Notify(args...);
+	}
+
+private:
+	std::vector<Observer> observers;
+};
+
+#endif  //!__OBSERVABLE_H__

dGame/Entity.cpp

@@ -96,6 +96,8 @@
 #include "CDSkillBehaviorTable.h"
 #include "CDZoneTableTable.h"
 
+Observable<Entity*, const PositionUpdate&> Entity::OnPlayerPositionUpdate;
+
 Entity::Entity(const LWOOBJID& objectID, EntityInfo info, User* parentUser, Entity* parentEntity) {
 	m_ObjectID = objectID;
 	m_TemplateID = info.lot;
@@ -2133,6 +2135,8 @@ void Entity::ProcessPositionUpdate(PositionUpdate& update) {
 	Game::entityManager->QueueGhostUpdate(GetObjectID());
 
 	if (updateChar) Game::entityManager->SerializeEntity(this);
+
+	OnPlayerPositionUpdate.Notify(this, update);
 }
 
 const SystemAddress& Entity::GetSystemAddress() const {

dGame/Entity.h

@@ -11,6 +11,7 @@
 #include "NiQuaternion.h"
 #include "LDFFormat.h"
 #include "eKillType.h"
+#include "Observable.h"
 
 namespace Loot {
 	class Info;
@@ -299,6 +300,11 @@ class Entity {
 	// Scale will only be communicated to the client when the construction packet is sent
 	void SetScale(const float scale) { m_Scale = scale; };
 
+	/**
+	 * @brief The observable for player entity position updates.
+	 */
+	static Observable<Entity*, const PositionUpdate&> OnPlayerPositionUpdate;
+
 protected:
 	LWOOBJID m_ObjectID;
 

dGame/dComponents/DestroyableComponent.cpp

@@ -38,6 +38,9 @@
 
 #include "CDComponentsRegistryTable.h"
 
+Implementation<bool, const Entity*> DestroyableComponent::IsEnemyImplentation;
+Implementation<bool, const Entity*> DestroyableComponent::IsFriendImplentation;
+
 DestroyableComponent::DestroyableComponent(Entity* parent) : Component(parent) {
 	m_iArmor = 0;
 	m_fMaxArmor = 0.0f;
@@ -418,6 +421,7 @@ void DestroyableComponent::AddFaction(const int32_t factionID, const bool ignore
 }
 
 bool DestroyableComponent::IsEnemy(const Entity* other) const {
+	if (IsEnemyImplentation.ExecuteWithDefault(other, false)) return true;
 	if (m_Parent->IsPlayer() && other->IsPlayer()) {
 		auto* thisCharacterComponent = m_Parent->GetComponent<CharacterComponent>();
 		if (!thisCharacterComponent) return false;
@@ -440,6 +444,7 @@ bool DestroyableComponent::IsEnemy(const Entity* other) const {
 }
 
 bool DestroyableComponent::IsFriend(const Entity* other) const {
+	if (IsFriendImplentation.ExecuteWithDefault(other, false)) return true;
 	const auto* otherDestroyableComponent = other->GetComponent<DestroyableComponent>();
 	if (otherDestroyableComponent != nullptr) {
 		for (const auto enemyFaction : m_EnemyFactionIDs) {

dGame/dComponents/DestroyableComponent.h

@@ -7,6 +7,7 @@
 #include "Entity.h"
 #include "Component.h"
 #include "eReplicaComponentType.h"
+#include "Implementation.h"
 
 namespace CppScripts {
 	class Script;
@@ -463,6 +464,9 @@ class DestroyableComponent final : public Component {
 	// handle hardcode mode drops
 	void DoHardcoreModeDrops(const LWOOBJID source);
 
+	static Implementation<bool, const Entity*> IsEnemyImplentation;
+	static Implementation<bool, const Entity*> IsFriendImplentation;
+
 private:
 	/**
 	 * Whether or not the health should be serialized