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

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 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, bool HasValue>
        struct passthrough_value
        {
            using type = T;
            using func = Func;
            constexpr static size_t index = Index;

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

        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<void, 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 decltype(std::get<0>(std::declval<result_types>))::type;

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

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

            template <typename T>
            using is_base_or_void = std::disjunction<std::is_void<typename T::type>, is_base<typename T::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<decltype(std::get<Indexes>(std::declval<result_types>()))>...>>;
            }

            constexpr static bool all_has_void = for_each_type<std::conjunction_v, std::is_void>(std::index_sequence_for<Args...>());
            constexpr static bool all_has_ret = for_each_type<std::conjunction_v, is_base>(std::index_sequence_for<Args...>());
            constexpr static bool all_has_ret_or_void = for_each_type<std::conjunction_v, is_base_or_void>(std::index_sequence_for<Args...>());

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

            template <size_t... Indexes>
            static constexpr auto make_variant(std::index_sequence<Indexes...>)
            {
                if constexpr (all_has_void)
                    return;
                using variant = variant_t<decltype(std::get<Indexes>(std::declval<non_void_types>()))...>;
                return std::declval<variant>();
            }

            static constexpr auto make_return_type()
            {
                if constexpr (all_has_void)
                    return;
                if constexpr (all_has_ret)
                    return std::declval<base_type>();
                if constexpr (all_has_ret_or_void)
                    return std::declval<std::optional<base_type>>();
                return 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 with empty default behavior
         * @param visitees user lambdas
         */
        template <typename... Visitee>
        constexpr auto visit(Visitee&&... visitees) -> decltype(detail::member_func_detail<std::tuple<Visitee...>, std::tuple<Types...>>::make_return_type())
        {
            return std::visit(lambda_visitor{
                           std::forward<Visitee>(visitees)...,
                           [](auto)
                           {
                           }
                       }, 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... MemberFuncs>
        constexpr auto call_member(const MemberFuncs... funcs)
        {
            static_assert(std::conjunction_v<std::is_member_function_pointer<std::decay_t<MemberFuncs>>...>,
                          "Must provide only pointers to member functions!");
            using meta_t = detail::member_func_detail<std::tuple<MemberFuncs...>, std::tuple<Types...>>;
            using result_t = decltype(meta_t::make_return_type());
            return std::visit([=](auto&& value) -> result_t
            {
                using ValueType = std::decay_t<decltype(value)>;

                if constexpr (std::disjunction_v<std::is_invocable<std::decay_t<decltype(funcs)>, ValueType>...>)
                {
                }

                return *(... || ([&](auto&& func) -> decltype(auto)
                {
                    using FuncType = std::decay_t<decltype(func)>;
                    using ReturnType = std::invoke_result_t<FuncType, ValueType>;
                    if constexpr (std::is_invocable_v<FuncType, ValueType>)
                    {
                        return ((value).*(func))();
                    }
                    return std::declval<result_t>();
                }(cast_member_ptr<std::decay_t<decltype(value)>>(std::forward<decltype(funcs)>(funcs)))));
            }, m_variant);
        }

        template <typename MemberFunc, typename... Args>
        constexpr auto call_member_args(const MemberFunc func, Args&&... args)
        {
            return std::visit([=](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