#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>; };

	namespace {

	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::NullDerefException<T>{};
#else
		__builtin_unreachable(); 
#endif
	return std::make_unique<T>(*c); }


	template<typename Error = ptr::NullException>
	constexpr decltype(auto) force_ok(auto&& mv) requires(std::is_convertible_v<decltype(mv), bool> && std::is_default_constructible_v<Error>)
	{
		struct err {
			[[gnu::noinline, gnu::cold, noreturn]]
			static constexpr void _throw() { throw Error{}; }
		};
		if( __builtin_expect(!bool(mv), false)) err::_throw();
		return std::forward<decltype(mv)>(mv);
	}

	} // _impl (anon)
	

	template<typename From, typename To>
	concept binary_convertible = std::is_convertible_v<From, To> and std::is_convertible_v<To, From>;

	template<typename From, typename To>
	concept polymorphic_castable = std::derived_from<std::decay_t<To>, std::decay_t<From>> 
					or std::derived_from<std::decay_t<From>, std::decay_t<To>>
					or std::is_same_v<std::decay_t<From>, std::decay_t<To>>
					or requires(std::decay_t<From> && from) {
		{ static_cast<std::decay_t<To> &&>(from) } -> std::convertible_to<To>;
	};

	template<polymorphic_castable<void> T>
	constexpr auto uniq_erase_type(std::unique_ptr<T>&& from) noexcept {
		struct deleter final /*: public ErasedTypeDeleter XXX <- Is this useful, for unerasing the type, maybe?*/ {
			typedef T type;

			
			/*[[gnu::cold, noreturn, gnu::noinline]]
			constexpr static void _throw() 
			{
				throw ptr::NullException{};
			}
		public:*/
			constexpr void opreator()(void *p) noexcept(std::is_nothrow_destructible_v<T>) {
			/*	T* ptr;
				if constexpr(DOES_CHECK) {
				 if(__builtin_expect(!(ptr = dynamic_cast<T*>(p)), false))
					_throw();
				} else ptr = static_cast<T*>(p); 
				delete ptr;*/
				delete static_cast<T*>(p);
			}
			constexpr T* back_cast(void *p) noexcept { return static_cast<T*>(p); }
			constexpr deleter() noexcept = default;
			constexpr deleter(deleter const&) noexcept = default;
			constexpr deleter(deleter &&) noexcept = default;
			constexpr deleter& operator=(deleter const&) noexcept = default;
			constexpr deleter& operator=(deleter &&) noexcept = default;

			constexpr ~deleter() noexcept = default;
		};
		return std::unique_ptr<void, deleter> {
			// Cannot retain type information of most-derived class from this: \
			dynamic_cast<void*>	
			static_cast<void*>
			(std::move(from).release())
			
		};
	}
	template<polymorphic_castable<void> T, typename D> requires(requires{ 
		typename std::unique_ptr<T, D>;
		requires(!std::is_same_v<std::unique_ptr<T, D>::deleter_type, std::unique_ptr<T>::deleter_type);
	})
	constexpr auto uniq_erase_type(std::unique_ptr<T, D>&& from) noexcept {
		class deleter final {
			D m_del;
		public:
			constexpr void operator()(void* p) noexcept(std::is_nothrow_invocable_v<D::operator(), T>) {
				m_del(static_cast<T*>(p));
			}

			constexpr T* back_cast(void* p) noexcept { return static_cast<T*>(p); }

			constexpr deleter(D&& deleter) noexcept(std::is_nothrow_move_constructible_v<D>)
				: m_del(std::move(deleter)) {}

			constexpr deleter() noexcept(std::is_nothrow_default_constructible_v<D>) requires(std::is_default_constructible_v<D>) =default;//: m_del() {}

			constexpr deleter(const deleter&) noexcept(std::is_nothrow_copy_constructible_v<D>) = default;
			constexpr deleter(deleter&&) noexcept(std::is_nothrow_move_constructible_v<D>) = default;

			constexpr deleter& operator=(const deleter&) noexcept(std::is_nothrow_copy_assignable_v<D>) = default;
			constexpr deleter& operator=(deleter&&) noexcept(std::is_nothrow_move_assignable_v<D>) = default;

			constexpr ~deleter() noexcept(std::is_nothrow_destructible_v<D>) requires(std::is_trivially_destructible_v<D>) = default;
			constexpr ~deleter() noexcept(std::is_nothrow_destructible_v<D>) {}
		};
		if constexpr(std::is_default_constructible_v<D>)
			return std::unique_ptr<void, deleter> {
				static_cast<void*>
				(std::move(from).release()), deleter()
			};
		else {
			deleter&& del{std::move(from.get_deleter())};
			return std::unique_ptr<void, deleter> {
				static_cast<void*>
				(std::move(from).release()), deleter{std::move(del)}
			};
		}
	}

	template<typename To, typename From> requires(polymorphic_castable<From, To>)
	constexpr std::unique_ptr<To> static_uniq_cast(std::unique_ptr<From>&& from) noexcept
	{
		return std::unique_ptr<To> { 
			static_cast<To*>( std::move(from).release() )
		};
	}

	template<typename To, typename From> requires(polymorphic_castable<From, To>)
	constexpr std::unique_ptr<To> dynamic_uniq_cast(std::unique_ptr<From>&& from) noexcept
	{
		return std::unique_ptr<To> { 
			dynamic_cast<To*>( std::move(from).release() )
		};
	}

	template<typename To, typename From, bool Check = false> requires(polymorphic_castable<From, To>)
	constexpr std::unique_ptr<To> uniq_cast(std::unique_ptr<From>&& from) noexcept
	{
		if constexpr(Check) return dynamic_uniq_cast(std::move(from));
		else return static_uniq_cast(std::move(from));
	}

	template<typename T>
	struct alignas(std::unique_ptr<T>) 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)))};
		}

		template<std::derived_from<T> U, bool Check = false>
		constexpr Box<U> upcast() && noexcept(!Check) 
		{ return Box<U> { force_ok(uniq_cast<U, T, Check>(std::move(m_ptr))) }; }

		template<typename U, bool Check = true> requires(std::derived_from<T, U>)
		constexpr Box<U> downcast() && noexcept(!Check)
		{ return Box<U> { force_ok(uniq_cast<U, T, Check>(std::move(m_ptr))) }; }

		template<polymorphic_castable<T> U, bool Check = !std::derived_from<U, T> > // Default dynamic check set to false only if we can statically determine that T is derived from U and the conversion is therfore infallible
		constexpr Box<U> polycast() && noexcept(!Check)
		{ return Box<U> { force_ok(uniq_cast<U, T, Check>(std::move(m_ptr))) }; }

		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(!_EO(DEBUG)) {
#if DEBUG
			ptr::throw_if_null(ptr);
#endif
			return Box<T>{ std::unique_ptr<T>{ ptr } };
		}

		constexpr static Box<T> from_raw_ptr(std::unique_ptr<T>&& uniq) {
			if(__builtin_expect(!bool(uniq), false)) ptr::throw_null_exception<T>();
			_EO_ASSUME(uniq.get() != nullptr);
			return Box<T> { std::move(uniq) };
		}

		constexpr static Box<T> from_raw_ptr_unchecked(std::unique_ptr<T>&& uniq) noexcept(!_EO(DEBUG)) {
#if DEBUG
			if(__builtin_expect(!uniq, false)) ptr::throw_null_exception<T>(); 
#else

			_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;
	protected:
		// For types that may need to invalidate the Box<T> guarantee without exposing it in API, they can inherit (non-virtual). 

		// For unsafe operations, wether or not to apply checks.
		enum unsafe_t {
			UNSAFE,
		};
		enum maybe_unsafe_t {
			CHECKED,
			DEBUG_CHECKED,
		};

		constexpr Box(util::exact_type<unsafe_t> auto u, std::unique_ptr<T>&& ptr) noexcept 
			: m_ptr(std::move(ptr)) { (void)u; }

		constexpr Box(util::exact_type<unsafe_t> auto u, Box const& copy) noexcept
			: m_ptr(uniq_clone(copy.as_unique(u))) {}

		constexpr static Box<T> from_raw_ptr(unsafe_t u, std::unique_ptr<T>&& uniq) noexcept {
			return Box{u, std::move(uniq)};
		}

		constexpr std::unique_ptr<T>& as_unique(unsafe_t) & noexcept { return m_ptr; }
		constexpr std::unique_ptr<T> const & as_unique(unsafe_t) const& noexcept { return m_ptr; }

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

		constexpr T* as_unsafe_ptr(unsafe_t) const noexcept { return m_ptr.get(); }
		constexpr std::unique_ptr<T> swap_unsafe_ptr(unsafe_t u, T* raw) noexcept 
		{ return (void)u; std::exchange(std::move(m_ptr), std::unique_ptr<T>{ raw }); }
		constexpr void set_unsafe_ptr(unsafe_t 8, T* raw) noexcept { 
			(void)u;
			m_ptr.reset(raw);
		}
		constexpr decltype(auto) set_unsafe(unsafe_t u, std::unique_ptr<T>&& ptr) noexcept 
		{ (void)u; return std::exchange(std::move(m_ptr), std::move(ptr)); }
		constexpr auto& swap_unsafe(unsafe_t, std::unique_ptr<T>& ptr) noexcept { 
			using std::swap;
			swap(m_ptr, ptr);
			return m_ptr;
		}

		constexpr T* release_unsafe(unsafe_t) noexcept { return m_ptr.release(); }
	private:
		constexpr explicit Box(std::unique_ptr<T>&& ptr) noexcept
			: m_ptr(std::move(ptr)) {
			_EO_ASSUME(m_ptr.get());
		}

		std::unique_ptr<T> m_ptr; // Unique<T> m_ptr;
	};
	static_assert(util::shares_layout<Box<_Complex double>, _Complex double*>, "Invalid Box<T> memory layout: More than just T*");
	static_assert(util::shares_layout<Box<_Complex double>, std::unique_ptr<_Complex double>>, "Invalid Box<T> memory layout: More than just std::unique_ptr<T>");

	template<typename T> concept is_boxable = is_boxable_v<T>;

	template<typename T>
	constexpr inline bool is_nothrow_boxable_v = is_boxable_v<T> && std::is_nothrow_constructible_v<Box<T>, T>;


	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;
		}
	} 

	template<typename T, typename U> requires(requires(T const& o) { static_cast<U const&>(o); })
	constexpr Box<U> dynamic_box_cast(Box<T> const& b) {
		return Box<U>::from_raw_ptr(std::addressof(dynamic_cast<U const&>(*b)));
	} 

#if 0
	template<typename T, typename R /*XXX: Maybe remove this, and put the requires after the definition, using `auto&& value` instead of `R&& value`*/> requires(std::derived_from<R, T>)
	constexpr Box<T> box(R&& value, util::comptime<bool> auto Check = _EO_CONSTANT_VALUE(false)) noexcept(std::is_nothrow_invocable_v< Box<T>::new_dynamic<R, util::comptime_eval_v<bool, Check>>) //XXX: This seems illegal...
	{ return Box<T>::template new_dynamic<R, Check>(std::move(value)); }

	template<typename T>
	constexpr Box<T> box(T&& value) noexcept(std::is_nothrow_constructible_v<Box<T>, T>)
	{ return { std::move(value) }; }
#endif
	template<typename T>
	constexpr Box<T> box(T&& value) noexcept(std::is_nothrow_constructible_v<Box<T>, decltype(value)>)
	{
		/*if constexpr(requires(decltype(value) v) { static_cast<T&&>(std::move(v)); }) {
			return Box<T>::template new_dynamic<T>(std::move(value));
		} else */return Box<T> { std::move(value) };
	}

	template<typename T>
	constexpr Box<T> box(std::unique_ptr<T>&& value) noexcept { return Box<T> { std::move(value) }; }

	template<typename Base, typename T> /*requires(polymorphic_castable<Base, T>)
	constexpr Box<Base> polybox(T&& value) noexcept
	{
		return Box<T>{ std::move(value) }.polycast<Base>()
	}*/ requires(std::derived_from<T, Base>)
	constexpr Box<Base> polybox(T&& value) noexcept {
		return Box<T>{ std::move(value) }.polycast<Base, false>(); // Convertion from derived to base infallible, no need for check.
	}

	template<typename Base, typename T> /*requires(polymorphic_castable<Base, T>)
	constexpr Box<Base> polybox(T&& value) noexcept
	{
		return Box<T>{ std::move(value) }.polycast<Base>()
	}*/ requires(std::derived_from<T, Base>)
	constexpr Box<Base> polybox(std::unique_ptr<T>&& value) noexcept {
		return Box<T>{ std::move(value) }.polycast<Base, false>(); // Convertion from derived to base infallible, no need for check.
	}
}
using boxed::Box;
}

//TODO: See phone notes on correctly implementing the nullopt for Box<T>
#if 0
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;
	};


}
#endif