mp.hpp

#pragma once
 
#include "type_traits.hpp"
#include "http/response.hpp"
 
#include <variant>
#include <type_traits>

namespace malloy::mp
{
 
    namespace detail
    {
        template<
            template<typename...> typename V,
            typename... Vargs
        >
        struct conv_to_resp_helper
        {
            using type = V<http::response<Vargs>...>;
 
            explicit
            constexpr
            conv_to_resp_helper(V<Vargs...>)
            {
            }
        };
    }

    template<typename V>
    using unwrap_variant = std::conditional_t<std::variant_size_v<V> == 1, std::variant_alternative_t<0, V>, V>;

    template<typename V>
    requires (malloy::concepts::is_variant_of_bodies<V>)
    using body_type = unwrap_variant<V>;

    // ToDo: Concept for F
    template<typename F>
    using bodies_for_t = std::invoke_result_t<decltype(&F::body_for), const F*, const typename F::header_type&>;

    template<typename Bodies>
    requires (malloy::concepts::is_variant_of_bodies<Bodies>)
    using to_responses = typename decltype(detail::conv_to_resp_helper{std::declval<Bodies>()})::type;

    // ToDo: Concept for Filter
    template<typename Filter>
    using filter_resp_t = unwrap_variant<to_responses<bodies_for_t<Filter>>>;
 
}