#pragma once

#include <functional>
#include <memory>
#include <mutex>
#include <shared_mutex>
#include <vector>

namespace openVulkanoCpp
{
	template<typename... Arguments>
	class Event final
	{
	public:
		typedef std::function<void(Arguments...)> Function;

	private:
		enum class EventHandlerType { STATIC, INSTANCED, INSTANCED_SHARED_PTR, INSTANCED_WEAK_PTR, FUNCTIONAL };

		class EventHandler
		{
			const EventHandlerType type;
		protected:
			EventHandler(EventHandlerType type) : type(type) {}
			virtual bool ShouldDelete(EventHandler* other) const = 0;

		public:
			virtual ~EventHandler() = default;

			bool ShouldBeDelete(EventHandler* other) const
			{
				if (other == this) return true;
				if (!other || other->type != type) return false;
				return ShouldDelete(other);
			}

			virtual void Notify(Arguments... args) const = 0;
		};

		class StaticEventHandler final : public EventHandler
		{
		public:
			typedef void (*Method)(Arguments...);

			StaticEventHandler(Method method) : EventHandler(EventHandlerType::STATIC), method(method) {}

			void Notify(Arguments... args) const override
			{
				method(args...);
			}

		protected:
			bool ShouldDelete(EventHandler* other) const override
			{
				return static_cast<StaticEventHandler*>(other)->method == this->method;
			}

		private:
			Method method;
		};

		template<class Instance, class Method>
		class InstancedEventHandler final : public EventHandler
		{
		public:
			InstancedEventHandler(Instance* instance, Method method) : EventHandler(EventHandlerType::INSTANCED), instance(instance), method(method) {}

			void Notify(Arguments... args) const override
			{
				(instance->*method)(args...);
			}

		protected:
			bool ShouldDelete(EventHandler* other) const override
			{
				InstancedEventHandler* otherHandler = static_cast<InstancedEventHandler*>(other);
				return otherHandler->instance == instance && otherHandler->method == this->method;
			}

		private:
			Instance* instance;
			Method method;
		};

		template<class Instance, class Method>
		class InstancedSharedPtrEventHandler final : public EventHandler
		{
		public:
			InstancedSharedPtrEventHandler(std::shared_ptr<Instance> instance, Method method) : EventHandler(EventHandlerType::INSTANCED_SHARED_PTR), instance(instance), method(method) {}

			void Notify(Arguments... args) const override
			{
				(instance.get()->*method)(args...);
			}

		protected:
			bool ShouldDelete(EventHandler* other) const override
			{
				InstancedSharedPtrEventHandler* otherHandler = static_cast<InstancedSharedPtrEventHandler*>(other);
				return otherHandler->instance == instance && otherHandler->method == this->method;
			}

		private:
			std::shared_ptr<Instance> instance;
			Method method;
		};

		template<class Instance, class Method>
		class InstancedWeakPtrEventHandler final : public EventHandler
		{
		public:
			InstancedWeakPtrEventHandler(std::weak_ptr<Instance> instance, Method method) : EventHandler(EventHandlerType::INSTANCED_WEAK_PTR), instance(instance), method(method) {}

			void Notify(Arguments... args) const override
			{
				if (auto instancePtr = instance.lock())
				{
					(instancePtr.get()->*method)(args...);
				}
			}

		protected:
			bool ShouldDelete(EventHandler* other) const override
			{
				InstancedWeakPtrEventHandler* otherHandler = static_cast<InstancedWeakPtrEventHandler*>(other);
				if (otherHandler->method == this->method)
				{
					if (auto ptr = instance.lock())
					{
						return ptr == otherHandler->instance.lock();
					}
					return true;
				}
				
				return false;
			}

		private:
			std::weak_ptr<Instance> instance;
			Method method;
		};

		class FunctionalEventHandler final : public EventHandler
		{
		public:
			FunctionalEventHandler(Function function) : EventHandler(EventHandlerType::FUNCTIONAL), function(function) {}

			void Notify(Arguments... args) const override
			{
				function(args...);
			}

		protected:
			bool ShouldDelete(EventHandler* other) const override
			{
				return false;
			}

		private:
			Function function;
		};

		std::vector<EventHandler*> handlers;
		mutable std::shared_mutex mutex;

		void Remove(EventHandler* referenceHandler)
		{
			std::unique_lock<std::shared_mutex> lock(mutex);
			for(size_t i = 0; i < handlers.size(); i++)
			{
				EventHandler* handler = handlers[i];
				if (handler->ShouldBeDelete(referenceHandler))
				{
					size_t end = handlers.size() - 1;
					if (i < end)
					{
						handlers[i] = handlers[end];
					}
					delete handler;
					handlers.pop_back();
				}
			}
		}

		void Add(EventHandler* handler)
		{
			std::unique_lock<std::shared_mutex> lock(mutex);
			handlers.push_back(handler);
		}

	public:
		void NotifyAll(Arguments... args) const
		{
			std::shared_lock<std::shared_mutex> lock(mutex);
			for(EventHandler* handler : handlers)
			{
				handler->Notify(args...);
			}
		}

		void operator()(Arguments... args)
		{
			NotifyAll(args);
		}

		template<class Instance, class Method>
		void RegisterHandler(Instance* instance, Method method)
		{
			Add(new InstancedEventHandler<Instance, Method>(instance, method));
		}

		template<class Instance, class Method>
		void UnregisterHandler(Instance* instance, Method method)
		{
			auto handler = InstancedEventHandler<Instance, Method>(instance, method);
	        Remove(&handler);
		}

		template<class Instance, class Method>
	    void operator +=(std::pair<Instance*, Method> instancedMethodPair)
		{
	        RegisterHandler(instancedMethodPair.first, instancedMethodPair.second);
	    }
	    
	    template<class Instance, class Method>
	    void operator -=(std::pair<Instance*, Method> instancedMethodPair)
		{
			UnregisterHandler(instancedMethodPair.first, instancedMethodPair.second);
	    }

		template<class Instance, class Method>
		void RegisterHandler(std::shared_ptr<Instance> instance, Method method)
		{
			Add(new InstancedSharedPtrEventHandler<Instance, Method>(instance, method));
		}

		template<class Instance, class Method>
		void UnregisterHandler(std::shared_ptr<Instance> instance, Method method)
		{
			auto handler = InstancedSharedPtrEventHandler<Instance, Method>(instance, method);
			Remove(&handler);
		}

		template<class Instance, class Method>
		void operator +=(std::pair<std::shared_ptr<Instance>, Method> instancedMethodPair)
		{
			RegisterHandler(instancedMethodPair.first, instancedMethodPair.second);
		}

		template<class Instance, class Method>
		void operator -=(std::pair<std::shared_ptr<Instance>, Method> instancedMethodPair)
		{
			UnregisterHandler(instancedMethodPair.first, instancedMethodPair.second);
		}

		template<class Instance, class Method>
		void RegisterHandler(std::weak_ptr<Instance> instance, Method method)
		{
			Add(new InstancedWeakPtrEventHandler<Instance, Method>(instance, method));
		}

		template<class Instance, class Method>
		void UnregisterHandler(std::weak_ptr<Instance> instance, Method method)
		{
			auto handler = InstancedWeakPtrEventHandler<Instance, Method>(instance, method);
			Remove(&handler);
		}

		template<class Instance, class Method>
		void RegisterHandlerWeak(std::weak_ptr<Instance> instance, Method method)
		{
			Add(new InstancedWeakPtrEventHandler<Instance, Method>(instance, method));
		}

		template<class Instance, class Method>
		void UnregisterHandlerWeak(std::weak_ptr<Instance> instance, Method method)
		{
			auto handler = InstancedWeakPtrEventHandler<Instance, Method>(instance, method);
			Remove(&handler);
		}

		template<class Instance, class Method>
		void operator +=(std::pair<std::weak_ptr<Instance>, Method> instancedMethodPair)
		{
			RegisterHandlerWeak(instancedMethodPair.first, instancedMethodPair.second);
		}

		template<class Instance, class Method>
		void operator -=(std::pair<std::weak_ptr<Instance>, Method> instancedMethodPair)
		{
			RegisterHandlerWeak(instancedMethodPair.first, instancedMethodPair.second);
		}

		void RegisterHandler(void (*method)(Arguments...))
		{
			handlers.push_back(new StaticEventHandler(method));
		}

		void UnregisterHandler(void (*method)(Arguments...))
		{
	        auto handler = StaticEventHandler(method);
	        Remove(&handler);
		}
	    
	    void operator +=(void (*method)(Arguments...))
		{
			RegisterHandler(method);
	    }
	    
	    void operator -=(void (*method)(Arguments...))
		{
			UnregisterHandler(method);
	    }

		EventHandler* RegisterHandler(Function function)
		{
			FunctionalEventHandler* handler = new FunctionalEventHandler(function);
			Add(handler);
			return handler;
		}

		void UnregisterHandler(EventHandler* handler)
		{
			Remove(handler);
		}
	    
	    EventHandler* operator +=(Function function)
		{
			return RegisterHandler(function);
	    }
	    
	    void operator -=(EventHandler* handler)
		{
			Remove(handler);
	    }
	};

	template<class Instance, class Method>
	constexpr std::pair<Instance*, Method> EventHandler(Instance* instance, Method method)
	{
		return std::pair<Instance*, Method>(instance, method);
	}

	template<class Instance, class Method>
	constexpr std::pair<std::shared_ptr<Instance>, Method> EventHandler(std::shared_ptr<Instance> instance, Method method)
	{
		return std::pair<std::shared_ptr<Instance>, Method>(instance, method);
	}

	template<class Instance, class Method>
	constexpr std::pair<std::weak_ptr<Instance>, Method> EventHandler(std::weak_ptr<Instance> instance, Method method)
	{
		return std::pair<std::weak_ptr<Instance>, Method>(instance, method);
	}

	template<class Instance, class Method>
	constexpr std::pair<std::weak_ptr<Instance>, Method> EventHandlerWeak(std::weak_ptr<Instance> instance, Method method)
	{
		return std::pair<std::weak_ptr<Instance>, Method>(instance, method);
	}
}