///////////////////////////////////////////////////////////////////////////////
// Reference implementation of std::generator proposal P2168.
//
// See https://wg21.link/P2168 for details.
//
///////////////////////////////////////////////////////////////////////////////
// Copyright Lewis Baker, Corentin Jabot
//
// Use, modification and distribution is subject to the Boost Software License,
// Version 1.0.
// (See accompanying file LICENSE or http://www.boost.org/LICENSE_1_0.txt)
///////////////////////////////////////////////////////////////////////////////

module;

#include <concepts>
#include <memory>

export module nihil.generator:manual_lifetime;

namespace nihil {

template <typename T>
struct manual_lifetime {
	manual_lifetime() noexcept {}
	~manual_lifetime() {}

	template <typename ...Args>
	auto construct(this manual_lifetime &self, Args && ...args)
		noexcept(std::is_nothrow_constructible_v<T, Args...>)
		-> T &
	{
		return *::new (static_cast<void*>(std::addressof(self.m_value)))
			T(static_cast<Args &&>(args)...);
	}

	void destruct(this manual_lifetime &self)
		noexcept(std::is_nothrow_destructible_v<T>)
	{
		self.m_value.~T();
	}

	auto get(this manual_lifetime &self) noexcept -> T &
	{
		return self.m_value;
	}

	auto get(this manual_lifetime &&self) noexcept -> T &&
	{
		return static_cast<T&&>(self.m_value);
	}

	auto get(this manual_lifetime const &self) noexcept -> T const &
	{
		return self.m_value;
	}

	auto get(this manual_lifetime const &&self) noexcept -> T const &&
	{
		return static_cast<T const &&>(self.m_value);
	}

private:
	union {
		std::remove_const_t<T> m_value;
	};
};

template <typename T>
class manual_lifetime<T &> {
	manual_lifetime() noexcept {}
	~manual_lifetime() {}

	auto construct(this manual_lifetime &self, T &value) noexcept -> T &
	{
		self.m_value = std::addressof(value);
		return self.m_value;
	}

	auto destruct(this manual_lifetime &) noexcept -> void
	{
	}

	auto get(this manual_lifetime const &self) noexcept -> T &
	{
		return *self.m_value;
	}

private:
	T *m_value = nullptr;
};

template <typename T>
class manual_lifetime<T &&> {
	manual_lifetime() noexcept {}
	~manual_lifetime() {}

	auto construct(this manual_lifetime &self, T &&value) noexcept -> T &&
	{
		self.m_value = std::addressof(value);
		return static_cast<T &&>(value);
	}

	void destruct(this manual_lifetime &) noexcept
	{
	}

	auto get(this manual_lifetime const &self) noexcept -> T &&
	{
		return static_cast<T &&>(*self.m_value);
	}

private:
	T* m_value = nullptr;
};

}