geode/loader/include/Geode/utils/conststring.hpp

#pragma once

#include <array>
#include <string_view>

using namespace std::string_view_literals;

namespace geode::utils {
    static constexpr const std::string_view sv_null = "\0";
    static constexpr const std::string_view sv_none = "";
    static constexpr const std::string_view sv_path = "/";

    // straight off
    // https://stackoverflow.com/questions/38955940/how-to-concatenate-static-strings-at-compile-time
    template <std::string_view const& Separator, std::string_view const&... Strs>
    struct ConstStringJoin {
        static constexpr auto impl() noexcept {
            constexpr std::size_t len =
                (Strs.size() + ... + 0) + (sizeof...(Strs) - 1) * Separator.size();
            std::array<char, len + 1> arr {};
            auto append = [len, i = 0, &arr](auto const& s) mutable {
                for (auto c : s)
                    arr[i++] = c;
                if (i < static_cast<int>(len - 1)) {
                    for (auto c : Separator)
                        arr[i++] = c;
                }
            };
            (append(Strs), ...);
            arr[len] = 0;
            return arr;
        }

        static constexpr auto arr = impl();
        static constexpr std::string_view value { arr.data(), arr.size() - 1 };
    };

    template <std::string_view const& Separator, std::string_view const&... Strs>
    static constexpr auto const_join_sep = ConstStringJoin<Separator, Strs...>::value;

    template <std::string_view const&... Strs>
    static constexpr auto const_join = ConstStringJoin<sv_none, Strs...>::value;

    template <std::string_view const&... Strs>
    static constexpr auto const_join_path = ConstStringJoin<sv_path, Strs...>::value;

    template <std::string_view const& Separator, std::string_view const&... Strs>
    static constexpr char const* const_join_sep_c_str =
        ConstStringJoin<Separator, Strs...>::value.data();

    template <std::string_view const&... Strs>
    static constexpr char const* const_join_c_str = ConstStringJoin<sv_none, Strs...>::value.data();

    template <std::string_view const&... Strs>
    static constexpr char const* const_join_path_c_str =
        ConstStringJoin<sv_path, Strs...>::value.data();
}