Component.h

#pragma once

namespace tinyxml2 {
	class XMLDocument;
}

namespace RakNet {
	class BitStream;
}

namespace GameMessages {
	struct GameMsg;
}

class Entity;

/**
 * Component base class, provides methods for game loop updates, usage events and loading and saving to XML.
 */
class Component {
public:
	Component(Entity* parent, const int32_t componentID) : m_Parent{ parent }, m_ComponentID{componentID} {}
	virtual ~Component() = default;

	/**
	 * Gets the owner of this component
	 * @return the owner of this component
	 */
	Entity* GetParent() const { return m_Parent; }

	[[nodiscard]] int32_t GetComponentID() const noexcept { return m_ComponentID; }

	/**
	 * Updates the component in the game loop
	 * @param deltaTime time passed since last update
	 */
	virtual void Update(float deltaTime) {}

	/**
	 * Event called when this component is being used, e.g. when some entity interacted with it
	 * @param originator
	 */
	virtual void OnUse(Entity* originator) {}

	/**
	 * Save data from this componennt to character XML
	 * @param doc the document to write data to
	 */
	virtual void UpdateXml(tinyxml2::XMLDocument& doc) {}

	/**
	 * Load base data for this component from character XML
	 * @param doc the document to read data from
	 */
	virtual void LoadFromXml(const tinyxml2::XMLDocument& doc) {}

	virtual void Serialize(RakNet::BitStream& outBitStream, bool isConstruction) {}
protected:
	template<typename GameObjClass, typename DerivedMsg>
	inline void RegisterMsg(bool (GameObjClass::*handler)(DerivedMsg&)) {
		static_assert(std::is_base_of_v<GameMessages::GameMsg, DerivedMsg>, "DerivedMsg must inherit from GameMsg");
		static_assert(std::is_base_of_v<Component, GameObjClass>, "GameObjClass must inherit from Component");
		const auto handlerBound = std::bind(handler, static_cast<GameObjClass*>(this), std::placeholders::_1);
		const auto castWrapper = [handlerBound](GameMessages::GameMsg& msg) {
			return handlerBound(static_cast<DerivedMsg&>(msg));
		};

		DerivedMsg msg;
		m_Parent->RegisterMsg(msg.msgId, castWrapper);
	}

	/**
	 * The entity that owns this component
	 */
	Entity* m_Parent;

	// The component ID, this should never be changed after initialization
	// This is used in various different ways
	// 1. To identify which entry this component is in its corresponding table
	// 2. To mark that an Entity should have the component with no database entry (it will be 0 in this case)
	// 3. The component exists implicitly due to design (CollectibleComponent always has a DestructibleComponent accompanying it). In this case the ID will be -1.
	const int32_t m_ComponentID;
};