#pragma once
/*
 *  Copyright (C) 2024  Brett Terpstra
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#ifndef BLT_STD_VARIANT_H
#define BLT_STD_VARIANT_H

#include <functional>
#include <optional>
#include <tuple>
#include <type_traits>
#include <variant>
#include <blt/std/types.h>

namespace blt
{
	template <typename... Types>
	class variant_t;

	namespace detail
	{
		template <typename... Ts>
		struct filter_void;

		template <>
		struct filter_void<>
		{
			using type = std::tuple<>;
		};

		template <typename T, typename... Ts>
		struct filter_void<T, Ts...>
		{
			using type = std::conditional_t<std::is_same_v<T, void>, typename filter_void<Ts...>::type, decltype(std::tuple_cat(
												std::declval<std::tuple<T>>(), std::declval<typename filter_void<Ts...>::type>()))>;
		};

		template <typename... Ts>
		using filter_void_t = typename filter_void<Ts...>::type;

		template <typename Type, typename... Ts>
		struct filter_invoke;

		template <typename Type>
		struct filter_invoke<Type>
		{
			using type = std::tuple<>;
		};

		template <typename Type, typename T, typename... Ts>
		struct filter_invoke<Type, T, Ts...>
		{
			using type = std::conditional_t<std::is_invocable_v<T, Type>, decltype(std::tuple_cat(
												std::declval<std::tuple<T>>(), std::declval<typename filter_invoke<Ts...>::type>())),
											typename filter_invoke<Ts...>::type>;
		};

		template <typename... Ts>
		using filter_invoke_t = typename filter_invoke<Ts...>::type;

		template <typename Type, typename Func>
		struct member_func_meta
		{
			using can_invoke = std::is_invocable<Func, Type>;

			using return_type = std::conditional_t<can_invoke::value, std::invoke_result_t<Func, Type>, void>;
		};

		template <typename T, typename Func, size_t Index>
		struct passthrough_value
		{
			using type = T;
			using func = Func;
			constexpr static size_t index = Index;

			bool has_value;

			explicit passthrough_value(const bool has_value): has_value(has_value)
			{}

			explicit operator bool() const
			{
				return has_value;
			}
		};

		template <typename Type, typename... Funcs>
		struct first_invoke_member_func
		{
			template <size_t... Indexes>
			constexpr static auto find_func(std::index_sequence<Indexes...>)
			{
				return (... || []() {
					using Meta = member_func_meta<Type, Funcs>;
					if constexpr (Meta::can_invoke::value)
					{
						return passthrough_value<typename Meta::return_type, Funcs, Indexes>{true};
					}
					return passthrough_value<typename Meta::return_type, Funcs, Indexes>{false};
				}());
			}

			using result = decltype(find_func(std::index_sequence_for<Funcs...>()));
			using return_type = typename result::type;
			using func_type = typename result::func;
			constexpr static size_t function_index = result::index;
		};

		template <typename FuncTuple, typename ArgTuple>
		struct member_func_detail;

		template <typename... Funcs, typename... Args>
		struct member_func_detail<std::tuple<Funcs...>, std::tuple<Args...>>
		{
			using result_types = std::tuple<first_invoke_member_func<Args, Funcs...>...>;
			using base_type = typename std::tuple_element_t<0, result_types>::return_type;

			template <typename T>
			using get_type = typename T::return_type;

			template <typename T>
			using is_base = std::is_same<T, base_type>;

			template <typename T>
			using is_base_or_void = std::disjunction<std::is_void<typename T::return_type>, is_base<typename T::return_type>>;

			template <template<typename...> typename Functor, template<typename> typename PerType, size_t... Indexes>
			constexpr static auto for_each_type(std::index_sequence<Indexes...>)
			{
				return std::declval<Functor<PerType<std::tuple_element_t<Indexes, result_types>>...>>;
			}

			constexpr static bool all_has_void = std::decay_t<std::invoke_result_t<decltype(for_each_type<std::conjunction, std::is_void>(
				std::index_sequence_for<Args...>()))>>::value;
			constexpr static bool all_has_ret = std::decay_t<std::invoke_result_t<decltype(for_each_type<std::conjunction, is_base>(
				std::index_sequence_for<Args...>()))>>::value;
			constexpr static bool all_has_ret_or_void = std::decay_t<std::invoke_result_t<decltype(for_each_type<std::conjunction, is_base_or_void>(
				std::index_sequence_for<Args...>()))>>::value;

			using non_void_types = typename std::decay_t<std::invoke_result_t<decltype(for_each_type<filter_void, get_type>(
				std::index_sequence_for<Args...>()))>>::type;

			template <size_t... Indexes>
			static constexpr auto make_variant(std::index_sequence<Indexes...>)
			{
				using variant = variant_t<std::decay_t<std::tuple_element_t<Indexes, non_void_types>>...>;
				return std::declval<variant>();
			}

			using make_return_type = std::conditional_t<all_has_void, void, std::conditional_t<
															all_has_ret, base_type, std::conditional_t<
																all_has_ret_or_void, std::optional<base_type>, std::conditional_t<
																	std::tuple_size_v<non_void_types> == 0, void, decltype(make_variant(
																		std::make_index_sequence<std::tuple_size_v<non_void_types>>{}))>>>>;
		};
	}

	/*
	* std::visit(blt::lambda_visitor{
	*      lambdas...
	* }, data_variant);
	*/

	template <typename... TLambdas>
	struct lambda_visitor : TLambdas...
	{
		using TLambdas::operator()...;
	};

	#if __cplusplus < 202002L

	// explicit deduction guide (not needed as of C++20)
	template <typename... TLambdas>
	lambda_visitor(TLambdas...) -> lambda_visitor<TLambdas...>;

	#endif

	template <typename... Types>
	class variant_t
	{
	public:
		using value_type = std::variant<Types...>;
		size_t variant_size = sizeof...(Types);

		constexpr variant_t(): m_variant()
		{}

		constexpr variant_t(const variant_t& variant) noexcept(std::is_nothrow_copy_constructible_v<value_type>): m_variant(variant.m_variant)
		{}

		constexpr variant_t(variant_t&& variant) noexcept(std::is_nothrow_move_constructible_v<value_type>): m_variant(std::move(variant.m_variant))
		{}

		explicit constexpr variant_t(const value_type& variant) noexcept(std::is_nothrow_copy_constructible_v<value_type>): m_variant(variant)
		{}

		explicit constexpr variant_t(value_type&& variant) noexcept(std::is_nothrow_move_constructible_v<value_type>): m_variant(std::move(variant))
		{}

		explicit constexpr variant_t(Types&&... args) noexcept(std::is_nothrow_constructible_v<value_type, Types...>): m_variant(
			std::forward<Types>(args)...)
		{}

		template <typename T, typename... C_Args>
		explicit constexpr variant_t(std::in_place_type_t<T>, C_Args&&... args): m_variant(std::in_place_type<T>, std::forward<C_Args>(args)...)
		{}

		template <typename T, typename U, typename... C_Args>
		constexpr explicit variant_t(std::in_place_type_t<T>, std::initializer_list<U> il, C_Args&&... args): m_variant(
			std::in_place_type<T>, il, std::forward<C_Args>(args)...)
		{}

		template <size_t I, typename... C_Args>
		explicit constexpr variant_t(std::in_place_index_t<I>, C_Args&&... args): m_variant(std::in_place_index<I>, std::forward<C_Args>(args)...)
		{}

		template <std::size_t I, typename U, typename... C_Args>
		constexpr explicit variant_t(std::in_place_index_t<I>, std::initializer_list<U> il, C_Args&&... args): m_variant(
			std::in_place_index<I>, il, std::forward<C_Args>(args)...)
		{}

		template <typename T, typename... Args>
		T& emplace(Args&&... args)
		{
			return m_variant.template emplace<T>(std::forward<Args>(args)...);
		}

		template <typename T, typename U, typename... Args>
		T& emplace(std::initializer_list<U> il, Args&&... args)
		{
			return m_variant.template emplace<T>(il, std::forward<Args>(args)...);
		}

		template <std::size_t I, typename... Args>
		std::variant_alternative_t<I, value_type>& emplace(Args&&... args)
		{
			return m_variant.template emplace<I>(std::forward<Args>(args)...);
		}

		template <std::size_t I, typename U, typename... Args>
		std::variant_alternative_t<I, value_type>& emplace(std::initializer_list<U> il, Args&&... args)
		{
			return m_variant.template emplace<I>(il, std::forward<Args>(args)...);
		}

		[[nodiscard]] constexpr std::size_t index() const noexcept
		{
			return m_variant.index();
		}

		[[nodiscard]] constexpr bool valueless_by_exception() const noexcept
		{
			return m_variant.valueless_by_exception();
		}

		template <typename T>
		constexpr auto visit(T&& visitor) -> decltype(auto)
		{
			return std::visit(std::forward<T>(visitor), m_variant);
		}

		/**
		* Automatic visitor generation
		* @param visitees user lambdas
		*/
		template <typename... Visitee>
		constexpr auto visit(
			Visitee&&... visitees) -> typename detail::member_func_detail<std::tuple<Visitee...>, std::tuple<Types...>>::make_return_type
		{
			return std::visit(lambda_visitor{std::forward<Visitee>(visitees)...}, m_variant);
		}

		template <typename Default, typename... Visitee>
		constexpr auto visit_value(Default&& default_value, Visitee&&... visitees) -> decltype(auto)
		{
			return std::visit(lambda_visitor{
				std::forward<Visitee>(visitees)...,
				[default_value=std::forward<Default>(default_value)](auto&& value) {
					return std::forward<decltype(value)>(value);
				}
			});
		}

		template <typename MemberFunc, typename... Args>
		constexpr auto call_member(const MemberFunc func,
									Args&&... args) -> typename detail::member_func_detail<
			std::tuple<MemberFunc>, std::tuple<Types...>>::make_return_type
		{
			return std::visit([func,...args=std::forward<Args>(args)](auto&& value) {
				return ((value).*(func))(std::forward<Args>(args)...);
			}, m_variant);
		}

		template <size_t I>
		[[nodiscard]] constexpr bool has_index() const noexcept
		{
			return m_variant.index() == I;
		}

		template <typename T>
		[[nodiscard]] constexpr bool has_type() const noexcept
		{
			return std::holds_alternative<T>(m_variant);
		}

		template <typename T>
		[[nodiscard]] constexpr auto get() -> decltype(auto)
		{
			return std::get<T>(m_variant);
		}

		template <typename T>
		[[nodiscard]] constexpr auto get() const -> decltype(auto)
		{
			return std::get<T>(m_variant);
		}

		template <size_t I>
		[[nodiscard]] constexpr auto get() -> decltype(auto)
		{
			return std::get<I>(m_variant);
		}

		template <size_t I>
		[[nodiscard]] constexpr auto get() const -> decltype(auto)
		{
			return std::get<I>(m_variant);
		}

		template <size_t I>
		constexpr std::add_pointer_t<std::variant_alternative_t<I, value_type>> get_if() noexcept
		{
			return std::get_if<I>(m_variant);
		}

		template <size_t I>
		constexpr std::add_pointer_t<const std::variant_alternative_t<I, value_type>> get_if() noexcept
		{
			return std::get_if<I>(m_variant);
		}

		template <typename T>
		constexpr std::add_pointer_t<T> get_if() noexcept
		{
			return std::get_if<T>(m_variant);
		}

		template <typename T>
		constexpr std::add_pointer_t<const T> get_if() noexcept
		{
			return std::get_if<T>(m_variant);
		}

		template <typename T>
		constexpr T value_or(T&& t) const
		{
			if (has_type<T>())
				return get<T>();
			return std::forward<T>(t);
		}

		template <size_t I>
		constexpr std::variant_alternative_t<I, value_type> value_or(const std::variant_alternative_t<I, value_type>& t) const
		{
			if (has_type<std::variant_alternative_t<I, value_type>>())
				return get<I>();
			return t;
		}

		template <size_t I>
		constexpr std::variant_alternative_t<I, value_type> value_or(std::variant_alternative_t<I, value_type>&& t) const
		{
			if (has_type<std::variant_alternative_t<I, value_type>>())
				return get<I>();
			return t;
		}

		template <size_t>
		constexpr const value_type& variant() const
		{
			return m_variant;
		}

		constexpr value_type& variant()
		{
			return m_variant;
		}

		[[nodiscard]] constexpr size_t size() const
		{
			return variant_size;
		}

		friend bool operator==(const variant_t& lhs, const variant_t& rhs)
		{
			return lhs.m_variant == rhs.m_variant;
		}

		friend bool operator!=(const variant_t& lhs, const variant_t& rhs)
		{
			return lhs.m_variant != rhs.m_variant;
		}

		friend bool operator<(const variant_t& lhs, const variant_t& rhs)
		{
			return lhs.m_variant < rhs.m_variant;
		}

		friend bool operator>(const variant_t& lhs, const variant_t& rhs)
		{
			return lhs.m_variant > rhs.m_variant;
		}

		friend bool operator<=(const variant_t& lhs, const variant_t& rhs)
		{
			return lhs.m_variant <= rhs.m_variant;
		}

		friend bool operator>=(const variant_t& lhs, const variant_t& rhs)
		{
			return lhs.m_variant >= rhs.m_variant;
		}

	private:
		template <typename Derived, typename Base, typename ReturnType, typename... Args>
		static auto cast_member_ptr(ReturnType (Base::*base_func)(Args...))
		{
			return reinterpret_cast<ReturnType (Derived::*)(Args...)>(base_func);
		}

		value_type m_variant;
	};

	namespace detail
	{
		template <typename>
		class variant_is_base_of
		{};

		template <typename... Types>
		class variant_is_base_of<variant_t<Types...>>
		{
		public:
			using value_type = bool;
			template <typename T>
			static constexpr bool value = std::conjunction_v<std::is_base_of<T, Types>...>;
		};

		template <typename... Types>
		class variant_is_base_of<std::variant<Types...>>
		{
		public:
			using value_type = bool;
			template <typename T>
			static constexpr bool value = std::conjunction_v<std::is_base_of<T, Types>...>;
		};

		template <typename T>
		static constexpr bool variant_is_base_of_v = variant_is_base_of<T>::value;
	}
}

#endif //BLT_STD_VARIANT_H