BansheeEngine/BansheeUtility/Include/BsServiceLocator.h

#pragma once

#include "BsPrerequisitesUtil.h"
#include "BsException.h"

namespace BansheeEngine
{
	/**
	* @brief	A locator system that allows you to quickly find a service of
	*			a specific type.
	*
	* @note		This is similar to a singleton pattern but unlike singleton the active instance 
	*			is not required to be available and can be replaced with another system during 
	*			runtime, or completely removed.
	*/
	template <class T>
	class ServiceLocator
	{
	public:
		/**
		 * @brief	Returns an instance of the service we are looking for,
		 *			if one is available.
		 *
		 * @note	Can return null.
		 */
		static T* instance() { return mService; }

		/**
		 * @brief	Starts providing a new service when "instance()" is called.
		 *			Replaces the previous service. 
		 */
		static void _provide(T* service)
		{
			mService = service;
		}

		/**
		 * @brief	Stops providing a service when "instance()" is called. Ignored if the current service
		 * 			doesn't match the provided service.
		 */
		static void _remove(T* service)
		{
			if (mService != service)
				return;

			mService = nullptr;
		}

	private:
		static T* mService;
	};

	template <class T>
	T* ServiceLocator<T>::mService = nullptr;
}