tuple.hpp

/*
 * Copyright (c) 2024 The RefValue Project
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 * THE SOFTWARE.
 */
 
#pragma once
 
#include <concepts>
#include <cstddef>
#include <limits>
#include <tuple>
#include <type_traits>
#include <utility>
 
namespace essence {
    template <auto GetTuple, auto Predicate>
    struct filter_tuple {
        static constexpr auto tuple = GetTuple();
 
        template <std::size_t I>
        static consteval auto do_single() noexcept {
            constexpr auto value = std::get<I>(tuple);
 
            if constexpr (Predicate(value)) {
                return std::tuple{value};
            } else {
                return std::tuple<>{};
            }
        }
 
        static consteval auto do_filter() noexcept {
            return []<std::size_t... Is>(std::index_sequence<Is...>) { return std::tuple_cat(do_single<Is>()...); }(
                       std::make_index_sequence<std::tuple_size_v<decltype(tuple)>>{});
        }
 
        static constexpr auto value = do_filter();
    };
 
    template <auto GetTuple, auto Predicate>
    inline constexpr auto filter_tuple_v = filter_tuple<GetTuple, Predicate>::value;
 
    template <typename... Ts, std::predicate<Ts...> Callable>
    constexpr std::size_t get_index_if(const std::tuple<Ts...>& tuple, Callable&& predicate) noexcept(
        (noexcept(std::declval<Callable>()(std::declval<Ts>())) && ...)) {
        return [&]<std::size_t... Is>(std::index_sequence<Is...>) {
            auto index = std::numeric_limits<std::size_t>::max();
 
            auto handler = [&]<std::size_t I>(std::integral_constant<std::size_t, I>) {
                if (index == std::numeric_limits<std::size_t>::max()
                    && std::forward<Callable>(predicate)(std::get<I>(tuple))) {
                    index = I;
                }
            };
 
            (handler(std::integral_constant<std::size_t, Is>{}), ...);
 
            return index;
        }(std::make_index_sequence<sizeof...(Ts)>{});
    }
} // namespace essence