draconisplusplus/include/rfl/parsing/Parser_optional.hpp

#ifndef RFL_PARSING_PARSER_OPTIONAL_HPP_
#define RFL_PARSING_PARSER_OPTIONAL_HPP_

#include <map>
#include <optional>
#include <type_traits>

#include "../Ref.hpp"
#include "../Result.hpp"
#include "../always_false.hpp"
#include "Parent.hpp"
#include "Parser_base.hpp"
#include "schema/Type.hpp"

namespace rfl {
  namespace parsing {

    template <class R, class W, class T, class ProcessorsType>
      requires AreReaderAndWriter<R, W, std::optional<T>>
    struct Parser<R, W, std::optional<T>, ProcessorsType> {
      using InputVarType  = typename R::InputVarType;
      using OutputVarType = typename W::OutputVarType;

      using ParentType = Parent<W>;

      static Result<std::optional<T>> read(const R& _r,
                                           const InputVarType& _var) noexcept {
        if (_r.is_empty(_var)) { return std::optional<T>(); }
        const auto to_opt = [](auto&& _t) { return std::make_optional<T>(_t); };
        return Parser<R, W, std::remove_cvref_t<T>, ProcessorsType>::read(_r,
                                                                          _var)
            .transform(to_opt);
      }

      template <class P>
      static void write(const W& _w,
                        const std::optional<T>& _o,
                        const P& _parent) noexcept {
        if (!_o) {
          ParentType::add_null(_w, _parent);
          return;
        }
        Parser<R, W, std::remove_cvref_t<T>, ProcessorsType>::write(_w, *_o,
                                                                    _parent);
      }

      static schema::Type to_schema(
          std::map<std::string, schema::Type>* _definitions) {
        using U = std::remove_cvref_t<T>;
        return schema::Type {schema::Type::Optional {Ref<schema::Type>::make(
            Parser<R, W, U, ProcessorsType>::to_schema(_definitions))}};
      }
    };

  } // namespace parsing
} // namespace rfl

#endif