#pragma once

#include <memory>
#include <utility>

#include "pointer.h"
#include "util.hh"

#include "exopt.h"

namespace exopt::types { namespace boxed {
	template<typename T>
	struct [[gnu::visibility("internal")]]  boxable_value_type { using type = std::conditional_t
			<std::is_reference_v<T>
			,std::reference_wrapper<std::remove_cvref_t<T> >
			,T>; };

	template<typename T>
	constexpr std::unique_ptr<T> uniq_clone(std::unique_ptr<T> const& c) noexcept(std::is_nothrow_copy_constructible_v<T>) requires(std::is_copy_constructible_v<T>)
	{ if(__builtin_expect(bool(c), true)) return std::make_unique<T>(*c); return nullptr; }

	template<typename T>
	constexpr std::unique_ptr<T> uniq_clone_unsafe(std::unique_ptr<T> const& c)
#ifndef DEBUG
		noexcept(std::is_nothrow_copy_constructible_v<T>) 
#endif
		requires(std::is_copy_constructible_v<T>)
	{ if(__builtin_expect(!bool(c), false)) 
#ifdef DEBUG
		throw ptr::NullException{}; 
#else
		__builtin_unreachable(); 
#endif
	return std::make_unique<T>(*c); }


	template<typename T>
	struct Box {
		typedef boxable_value_type<T>::type type;

		constexpr Box() noexcept(std::is_nothrow_default_constructible_v<T>) requires(std::is_default_constructible_v<T>)
			: m_ptr{std::make_unique<T>()} {}

		template<typename... Args> requires(std::is_constructible_v<T, Args...>)
		constexpr Box(Args&&... ctor) noexcept(std::is_nothrow_constructible_v<T, Args...>)
			: m_ptr{std::make_unique<T>(std::forward<Args>(ctor)...)} {}

		constexpr Box(T&& value) noexcept(std::is_nothrow_constructible_v<T>)
			: m_ptr{std::make_unique<T>(std::move(value))} {}

		constexpr Box(Box&&) noexcept = default;
		constexpr Box& operator=(Box&&) noexcept = default;
		constexpr Box(const Box& copy) noexcept(std::is_nothrow_copy_constructible_v<T>) requires(std::is_copy_constructible_v<T>)
			: m_ptr{uniq_clone_unsafe(copy.m_ptr)} {}
		constexpr Box& operator=(Box const& copy) noexcept(std::is_nothrow_copy_assignable_v<T>) requires(std::is_copy_assignable_v<T>)
		{
			if(__builtin_expect(this != std::addressof(copy), true)) {
				m_ptr = uniq_clone_unsafe(copy.m_ptr);
			} return *this;
		}

	//TODO: Accessors, `(explicit?) operator std::unique_ptr<T> const&[&]`?, etc.

		constexpr ~Box() = default;
	private:
		std::unique_ptr<T> m_ptr; // Unique<T> m_ptr;
	};
}
using boxed::Box;
}

namespace exopt::types { namespace optional [[gnu::visibility("internal")]] {
	template<typename T>
	struct null_optimise<boxed::Box<T> > { constexpr static inline bool value = true;
	//XXX: Eh.. Idk if Option<T>'s lifetime design can make this work...
		using held_type = boxed::Box<T>;
		using type = boxed::Box<T>&;
		constexpr static decltype(auto) convert_to_held(std::add_rvalue_reference_t<type> t) noexcept { return std::move(t); }
		constexpr static decltype(auto) convert_from_held(std::add_rvalue_reference_t<held_type> t) noexcept { return std::forward<type>(t); }

		constexpr static inline T* sentinel = nullptr;
	};


}