argparser/src/optional-arg.h

#ifndef ARGPARSER_OPTIONAL_ARG_H
#define ARGPARSER_OPTIONAL_ARG_H

#include "argument.h"
#include "errors.h"
#include "parse-result.h"
#include "type.h"
#include <any>
#include <cassert>
#include <memory>
#include <optional>
#include <span>
#include <string>

namespace argparser {

    template<typename T>
    class optional_arg : public arg, public std::enable_shared_from_this<optional_arg<T>> {
    public:
        optional_arg(std::string name, type_handle_impl<T> type) : arg(std::move(name)), type(type) {}

        std::shared_ptr<optional_arg<T>> default_value(T val) {
            default_value_ = val;
            return this->shared_from_this();
        }

        [[nodiscard]] std::optional<T> get(const parse_result &p) const {
            auto v = p.get_arg(name);
            if (!v.has_value()) {
                if (default_value_.has_value()) {
                    return default_value_.value();
                }
                return std::nullopt;
            }
            return std::make_optional(std::any_cast<T>(v));
        }

        [[nodiscard]] bool has(const parse_result &p) const {
            return p.has_arg(name);
        }

    private:
        type_handle_impl<T> type;
        std::optional<T> default_value_ = std::nullopt;

        void do_parse(std::string input, parse_result &pr) const override {
            assert(!pr.get_arg(name).has_value());// an optional arg can only be parsed once
            auto val = this->parse_single_value(input, type);
            pr.set_arg(name, std::make_any<T>(val));
        }

        [[nodiscard]] bool get_can_parse_more(parse_result &pr) const override {
            return !pr.get_arg(name).has_value();
        }

        [[nodiscard]] bool get_has_parsed_enough(parse_result &) const override {
            return true;
        }
    };

    template<typename T>
    using optional_arg_handle = std::shared_ptr<optional_arg<T>>;

}// namespace argparser

#endif//ARGPARSER_OPTIONAL_ARG_H