gplib/include/gp/functional/variant.hpp

#pragma once

#include "gp_config.hpp"

#include <gp/algorithms/move.hpp>
#include <gp/algorithms/tmp_manip.hpp>
#include "gp/utils/allocators/dummy.hpp"
#include "gp/exception.hpp"
#include "gp/functional/function.hpp"

#include <type_traits>
#include <new>

// TODO: Implement the allocating flavour of variant

namespace gp{

	/**
	 * @brief A form of variant that expect only classes whose size is strictly defined at compile time
	 * 
	 * @tparam T The list of types accepted by the variant
	 */
	template<typename ...T>
	class fixed_variant final {
		std::size_t index = std::numeric_limits<std::size_t>::max();
		alignas(gp::max(alignof(T)...)) char data[max_size<T...>()];
		gp::function<void(void*, void*)> cpytor = {[](void*, void*){}, nullopt};
		gp::function<void(void*, void*)> mvtor = {[](void*, void*){}, nullopt};
		gp::function<void(void*)> dtor = {[](void*){}, nullopt};
		static_assert(all_of_fixed_size<T...>::value, "not fixed");

	public:
		fixed_variant()
		: fixed_variant(typename first_of<T...>::type{})
		{}

		/**
		 * @brief Construct a new fixed variant from an object that is legal in it
		 * 
		 * @tparam U A type that belongs in the list of types the variant supports
		 * @param value The copied value
		 */
		template<typename U, std::enable_if_t<list_contains_class<gp::remove_cvref_t<U>,T...>::value,int> = 0>
		fixed_variant(U& value)
		: index{r_index_of<gp::remove_cvref_t<U>, T...>::value}
		{
			using actual = gp::remove_cvref_t<U>;
			dtor = gp::function<void(void*)>([](void* thing){
				((actual*)thing)->~actual();
			}, nullopt);
			cpytor = gp::function<void(void*, void*)>([](void* src, void* dest){
				new(dest) actual(*(actual*)src);
			}, nullopt);
			mvtor = gp::function<void(void*, void*)>([](void* src, void* dest){
				new(dest) actual(gp::move(*(actual*)src));
			}, nullopt);
			cpytor((char*)&value, data);
		}

		static_assert(list_contains_class<int, int>::value, "list_contains_class doesn't work properly");
		static_assert(list_contains_class<int, char, int>::value, "list_contains_class doesn't work properly");
		static_assert(list_contains_class<int, int, char>::value, "list_contains_class doesn't work properly");
		static_assert(list_contains_class<int, char, int, char>::value, "list_contains_class doesn't work properly");
		static_assert(!list_contains_class<int, char, char>::value, "list_contains_class doesn't work properly");

		/**
		 * @brief Construct a new fixed variant from an object that is legal in it by moving said object
		 * 
		 * @tparam U A type that belongs in the list of types the variant supports
		 * @param value The moved value
		 */
		template<typename U, std::enable_if_t<list_contains_class<gp::remove_cvref_t<U>,T...>::value,int> = 0>
		fixed_variant(U&& value)
		: index{r_index_of<gp::remove_cvref_t<U>, T...>::value}
		{
			using actual = gp::remove_cvref_t<U>;
			dtor = gp::function<void(void*)>([](void* thing){
				((actual*)thing)->~actual();
			}, nullopt);
			cpytor = gp::function<void(void*, void*)>([](void* src, void* dest){
				new(dest) actual(*(actual*)src);
			}, nullopt);
			mvtor = gp::function<void(void*, void*)>([](void* src, void* dest){
				new(dest) actual(gp::move(*(actual*)src));
			}, nullopt);
			mvtor((char*)&value, data);
		}

		fixed_variant(const fixed_variant& oth)
		: index{oth.index}
		, dtor{oth.dtor}
		, cpytor{oth.cpytor}
		, mvtor{oth.mvtor}
		{
			cpytor((char*)oth.data, (char*)data);
		}

		fixed_variant(fixed_variant& oth)
		: index{oth.index}
		, dtor{oth.dtor}
		, cpytor{oth.cpytor}
		, mvtor{oth.mvtor}
		{
			cpytor(oth.data, data);
		}

		fixed_variant(fixed_variant&& oth)
		: index{oth.index}
		, dtor{oth.dtor}
		, cpytor{oth.cpytor}
		, mvtor{oth.mvtor}
		{
			oth.index = std::numeric_limits<std::size_t>::max();
			mvtor(oth.data, data);
		}

		/**
		 * @brief Gives an alternative (value usable in a switch statement) representing the given type
		 * 
		 * @tparam U the type to match against
		 * @return constexpr size_t a value that can be used in the case part of a switch case statement
		 * @see type()
		 */
		template<typename U>
		constexpr static size_t alt() {
			return r_index_of<U, T...>::value;
		}

		/**
		 * @brief Gives the type as can be matched in a switch statement using alternatives
		 * 
		 * @return size_t a value that can be used in the switch part of a switch case statement
		 * @see alt()
		 */
		size_t type() const {
			return index;
		}

		void operator=(fixed_variant& value)
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor((void*)data);
			}
			index = value.index;
			cpytor = value.cpytor;
			dtor = value.dtor;
			mvtor = value.mvtor;
			cpytor(value.data, data);
		}

		void operator=(fixed_variant&& value)
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor((void*)data);
			}
			dtor = value.dtor;
			cpytor = value.cpytor;
			mvtor = value.mvtor;
			index = value.index;
			value.index = std::numeric_limits<std::size_t>::max();
			mvtor(value.data, data);
		}

		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		void operator=(U& value)
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor((void*)data);
			}
			index = r_index_of<gp::remove_cvref_t<U>, T...>::value;
			new(data) U(value);
			dtor = gp::function([](void* thing){((U*)thing)->~U();}, nullopt);
			cpytor = gp::function<void(void*, void*)>([](void* src, void* dest){new(dest) U(*(U*)src);}, nullopt);
			mvtor = gp::function<void(void*, void*)>([](void* src, void* dest){new(dest) U(gp::move(*(U*)src));}, nullopt);
		}

		template<typename U, typename std::enable_if<list_contains_class<U,T...>::value,int>::type>
		void operator=(U&& value)
		{
			if(index != std::numeric_limits<std::size_t>::max())
			{
				dtor((void*)data);
			}
			new(data) U(gp::move(value));
			index = r_index_of<gp::remove_cvref_t<U>, T...>::value;
			dtor = gp::function([](void* thing){((U*)thing)->~U();}, nullopt);
			cpytor = gp::function<void(void*, void*)>([](void* src, void* dest){new(dest) U(*(U*)src);}, nullopt);
			mvtor = gp::function<void(void*, void*)>([](void* src, void* dest){new(dest) U(gp::move(*(U*)src));}, nullopt);
		}

		~fixed_variant()
		{
			if(index != std::numeric_limits<std::size_t>::max() && dtor.ready())
			{
				dtor((void*)data);
				index = std::numeric_limits<std::size_t>::max();
			}
		}

		/**
		 * @brief Brutally decay the variant into the given type. 
		 Will throw (@see bad_variant_access) if exceptions are enabled, else behaviour is undefined.
		 * 
		 * @tparam U the type to decay towards
		 * @return constexpr U& a decayed reference to the variant
		 */
		template<typename U>
		constexpr U& value()
		{
			if constexpr (gp_config::has_exceptions)
			{
				if(r_index_of<gp::remove_cvref_t<U>, T...>::value != index)
				{
					throw bad_variant_access<U>{};
				}
			}
			return *reinterpret_cast<U*>(data);
		}

		/**
		 * @brief Tests if the variant is of a particular type.
		 * 
		 * @tparam U the type to match against
		 * @return true if the types match 
		 * @return false if the types don't match
		 */
		template<typename U>
		constexpr bool is_a()
		{
			if(r_index_of<gp::remove_cvref_t<U>, T...>::value == index)
			{
				return true;
			}
			else
			{
				return false;
			}
		}
	};
}