flag.hpp

// Copyright (C) 2022-2023 by Camden Mannett.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "arg_router/policy/default_value.hpp"
#include "arg_router/policy/description.hpp"
#include "arg_router/policy/long_name.hpp"
#include "arg_router/policy/min_max_count.hpp"
#include "arg_router/policy/short_form_expander.hpp"
#include "arg_router/policy/short_name.hpp"
#include "arg_router/tree_node.hpp"
#include "arg_router/utility/string_to_policy.hpp"
 
namespace arg_router
{
template <typename... Policies>
class flag_t :
    public tree_node<policy::default_value<bool>,
                     policy::min_max_count_t<traits::integral_constant<std::size_t{0}>,
                                             traits::integral_constant<std::size_t{0}>>,
                     std::decay_t<Policies>...>
{
    static_assert(policy::is_all_policies_v<std::tuple<std::decay_t<Policies>...>>,
                  "Flags must only contain policies (not other nodes)");
 
    using parent_type =
        tree_node<policy::default_value<bool>,
                  policy::min_max_count_t<traits::integral_constant<std::size_t{0}>,
                                          traits::integral_constant<std::size_t{0}>>,
                  std::decay_t<Policies>...>;
 
    static_assert(traits::has_long_name_method_v<flag_t> || traits::has_short_name_method_v<flag_t>,
                  "Flag must have a long and/or short name policy");
    static_assert(!traits::has_display_name_method_v<flag_t>,
                  "Flag must not have a display name policy");
    static_assert(!traits::has_none_name_method_v<flag_t>, "Flag must not have a none name policy");
 
public:
    using typename parent_type::policies_type;
 
    using value_type = bool;
 
    template <bool Flatten>
    using help_data_type = typename parent_type::template default_leaf_help_data_type<Flatten>;
 
    constexpr explicit flag_t(Policies... policies) noexcept :
        parent_type{policy::default_value<bool>{false},
                    policy::min_max_count_t<traits::integral_constant<std::size_t{0}>,
                                            traits::integral_constant<std::size_t{0}>>{},
                    std::move(policies)...}
    {
    }
 
    template <typename Validator, bool HasTarget, typename... Parents>
    [[nodiscard]] std::optional<parsing::parse_target> pre_parse(
        parsing::pre_parse_data<Validator, HasTarget> pre_parse_data,
        const Parents&... parents) const
 
    {
        return parent_type::pre_parse(pre_parse_data, *this, parents...);
    }
 
    template <typename... Parents>
    value_type parse([[maybe_unused]] parsing::parse_target&& target,
                     [[maybe_unused]] const Parents&... parents) const
    {
        // Presence of the flag yields a constant true
        const auto result = true;
 
        // Routing phase
        using routing_policy =
            typename parent_type::template phase_finder_t<policy::has_routing_phase_method>;
        if constexpr (!std::is_void_v<routing_policy>) {
            this->routing_policy::routing_phase(result);
        }
 
        return result;
    }
 
private:
    static_assert(!parent_type::template any_phases_v<value_type,
                                                      policy::has_parse_phase_method,
                                                      policy::has_validation_phase_method>,
                  "Flag does not support policies with parse or validation phases "
                  "(e.g. custom_parser or min_max_value)");
};
 
template <typename... Policies>
[[nodiscard]] constexpr auto flag(Policies... policies) noexcept
{
    return std::apply(
        [](auto... converted_policies) {
            // Add the short-form expander if one of the policies implements the short name method,
            // and if the short and long prefix are not the same
            constexpr auto has_short_name =
                boost::mp11::mp_any_of<std::tuple<std::decay_t<decltype(converted_policies)>...>,
                                       traits::has_short_name_method>::value;
            if constexpr ((config::long_prefix != config::short_prefix) && has_short_name) {
                return flag_t{policy::short_form_expander, std::move(converted_policies)...};
            } else {
                return flag_t{std::move(converted_policies)...};
            }
        },
        utility::string_to_policy::convert<
            utility::string_to_policy::first_string_mapper<policy::long_name_t>,
            utility::string_to_policy::second_string_mapper<policy::description_t>,
            utility::string_to_policy::single_char_mapper<policy::short_name_t>>(
            std::move(policies)...));
}
}  // namespace arg_router