libexopt/include/boxed.h

#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;

		template<std::derived_from<T> U, bool RuntimeCheck=false>
		constexpr static Box<T> new_dynamic(U&& v) noexcept(!RuntimeCheck) {
			if constexpr(!RuntimeCheck) {
				auto boxed = std::make_unique<U>(std::move(v));
				return Box<T>{std::unique_ptr<T>{static_cast<T*>(boxed.release())}};
			} else
			return Box<T>{std::make_unique<T>(dynamic_cast<T&&>(std::move(v)))};
		}

		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;
		}

		[[gnu::nonnull(1)]]
		constexpr static Box<T> from_raw_ptr(T* ptr) noexcept {
			return Box<T>{ std::unique_ptr<T>{ ptr } };
		}
		constexpr static Box<T> from_raw_ptr(std::unique_ptr<T>&& uniq) 
#if DEBUG
			{ if(__builtin_expect(!uniq, false)) throw ptr::NullException{};
#else

			noexcept {
			_EO_ASSUME(uniq.get() != nullptr);
#endif
			return Box<T>{ std::move(uniq) };
		}
		[[gnu::returns_nonnull]]
		constexpr T* get() const noexcept { return m_ptr.get(); }
		[[gnu::returns_nonnull]]
		constexpr T* release() noexcept { return m_ptr.release(); }

		constexpr std::unique_ptr<T>&& into_unique() &&noexcept { return std::move(m_ptr); }

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

		constexpr ~Box() = default;
	private:
		constexpr explicit Box(std::unique_ptr<T>&& ptr)
			: m_ptr(std::move(ptr)) {
			_EO_ASSUME(m_ptr.get());
		}

		std::unique_ptr<T> m_ptr; // Unique<T> m_ptr;
	};

	template<typename T, typename U> requires(requires(T&& o) { static_cast<U&&>(o); })
	constexpr Box<U> static_box_cast(Box<T>&& b) noexcept { return Box<U>::from_raw_ptr(static_cast<U*>(b.release())); }

	template<typename T, typename U> requires(requires(T&& o) { static_cast<U&&>(o); })
	constexpr Box<U> dynamic_box_cast(Box<T>&& b) {	
		auto* rel = b.release();
		try {
			return Box<U>::from_raw_ptr(std::addressof(dynamic_cast<U&&>(std::move(*rel))));
		} catch(...) {
			delete rel;
			throw;
		}
	} //TODO: Overload for `const&` that does the type check *before* the copy allocation.
}
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;
	};


}