#pragma once

//#define WIN32_LEAN_AND_MEAN

#include <Windows.h>
#include <concepts>
#include <type_traits>

#include <LdH/exception.hpp>


namespace LdH::Asyncio {
#if 0
	template<class ret_t, template<typename> class lambda_t>
	concept OverlappedFunc = std::invocable<lambda_t<ret_t>, LPOVERLAPPED, LPOVERLAPPED_COMPLETION_ROUTINE>
							 && std::same_as<std::invoke_result_t<lambda_t<ret_t>, LPOVERLAPPED, LPOVERLAPPED_COMPLETION_ROUTINE>, ret_t>;
#endif

	template<class lambda_t>
	concept OverlappedFunc = std::invocable<lambda_t, LPOVERLAPPED, LPOVERLAPPED_COMPLETION_ROUTINE>
							 && std::same_as<std::invoke_result_t<lambda_t, LPOVERLAPPED, LPOVERLAPPED_COMPLETION_ROUTINE>, DWORD>;

	class WindowsOverlappedEventloop {

	private:
		static thread_local struct _running_loop_variable_t {
		private:
			WindowsOverlappedEventloop *_value;

		public:
			[[nodiscard]]
			WindowsOverlappedEventloop *get() {
				auto cached = this->_value;
				if (cached == nullptr) throw LdH::Exception{"No running loop"};
				return cached;
			}

			[[nodiscard]]
			WindowsOverlappedEventloop *getOrNull() {
				return this->_value;
			}

			void set(WindowsOverlappedEventloop *v) {
				if (this->_value != nullptr && v != nullptr) throw LdH::Exception{"Recursive loops not allowed"};
				this->_value = v;
			}
		} _running_loop;

		struct FiberMetadata {
		public:
			OVERLAPPED overlapped;

			void *fiber_id;

			FiberMetadata *next_existing;
			FiberMetadata *prev_existing;
			FiberMetadata *next_active;
			FiberMetadata *prev_active;

			DWORD err_code;
			DWORD read_count;
		};


		HANDLE const notifier;
		bool const need_rollback_to_thread;
		void *const master_fiber;
		bool interrupted;
		FiberMetadata *next_existing;
		FiberMetadata *next_active;
		DWORD const fls_fiber_metadata;
		void *fiber_to_destroy;

	public:
		WindowsOverlappedEventloop();

		~WindowsOverlappedEventloop();

	private:
		[[nodiscard]]
		HANDLE createEvent() const;

		[[nodiscard]]
		HANDLE prepareFibers() const;

		[[nodiscard]]
		DWORD allocFls() const;

	public:
		void runUntilHasTasksAndNotInterrupted();

	private:
		void _addTask(void (*routine)(void *), void *arg);

		static void _overlapped_completion_routine(DWORD dwErrorCode, DWORD dwNumberOfBytesTransfered, FiberMetadata *lpOverlapped);

	public:
		template<class T>
		static void addTaskToRuningLoop(void (*routine)(T *), T *arg) {
			WindowsOverlappedEventloop::_running_loop.get()->_addTask(
					reinterpret_cast<void (*)(void *)>(routine),
					reinterpret_cast<void *>(arg)
			);
		}

		template<class T>
		void addTask(void (*routine)(T *), T *arg) {
			this->_addTask(
					reinterpret_cast<void (*)(void *)>(routine),
					reinterpret_cast<void *>(arg)
			);
		}

		static DWORD overlappedCall(OverlappedFunc auto func) {
			auto loop = WindowsOverlappedEventloop::_running_loop.get();
			auto metadata = reinterpret_cast<FiberMetadata *>(FlsGetValue(loop->fls_fiber_metadata));
			if (metadata == nullptr) LdH::Exception::throwFromLastWindowsErr();

			DWORD read_count = func(reinterpret_cast<LPOVERLAPPED>(metadata), reinterpret_cast<LPOVERLAPPED_COMPLETION_ROUTINE>(&WindowsOverlappedEventloop::_overlapped_completion_routine));
			if (read_count != 0) return read_count;

			if (loop->next_active == metadata)
				loop->next_active = metadata->next_active;
			if (metadata->next_active != nullptr)
				metadata->next_active->prev_active = metadata->prev_active;
			if (metadata->prev_active != nullptr)
				metadata->prev_active->next_active = metadata->next_active;
			metadata->next_active = nullptr;
			metadata->prev_active = nullptr;

			SwitchToFiber(loop->master_fiber);

			if (metadata->err_code != ERROR_SUCCESS)
				LdH::Exception::throwFromWindowsErrCode(metadata->err_code);
			return metadata->read_count;
		}

		static void interruptEventLoop() {
			WindowsOverlappedEventloop::_running_loop.get()->interrupted = true;
		}

	private:
		struct FiberInitializer {
			WindowsOverlappedEventloop *loop;

			void (*routine)(void *);

			void *routine_arg;
			void *caller_fiber;
		};

		static void fiber_kernel(FiberInitializer *init);
	};
}