draconisplusplus/include/rfl/parsing/Parser_result.hpp

#ifndef RFL_PARSING_PARSER_RESULT_HPP_
#define RFL_PARSING_PARSER_RESULT_HPP_

#include <map>
#include <type_traits>

#include "../Result.hpp"
#include "../always_false.hpp"
#include "../internal/StringLiteral.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, Result<T>>
    struct Parser<R, W, Result<T>, ProcessorsType> {
      using InputVarType  = typename R::InputVarType;
      using OutputVarType = typename W::OutputVarType;

      using ErrorType   = NamedTuple<Field<"error", std::string>>;
      using VariantType = std::variant<std::remove_cvref_t<T>, ErrorType>;

      static Result<Result<T>>
      read(const R& _r, const InputVarType& _var) noexcept {
        const auto handle = [](auto&& _t) -> Result<T> {
          using Type = std::remove_cvref_t<decltype(_t)>;
          if constexpr (std::is_same<Type, ErrorType>()) {
            return Error(_t.template get<"error">());
          } else {
            return std::forward<std::remove_cvref_t<T>>(_t);
          }
        };

        const auto to_res = [&](VariantType&& _v) -> Result<T> {
          return std::visit(handle, std::forward<VariantType>(_v));
        };

        return Result<Result<T>>(
            Parser<R, W, VariantType, ProcessorsType>::read(_r, _var).transform(
                to_res
            )
        );
      }

      template <class P>
      static void
      write(const W& _w, const Result<T>& _r, const P& _parent) noexcept {
        const auto write_t = [&](const auto& _t) -> Nothing {
          Parser<R, W, std::remove_cvref_t<T>, ProcessorsType>::write(
              _w, _t, _parent
          );
          return Nothing {};
        };

        const auto write_err = [&](const auto& _err) -> Nothing {
          Parser<R, W, ErrorType, ProcessorsType>::write(
              _w, ErrorType(make_field<"error">(_err.what())), _parent
          );
          return Nothing {};
        };

        _r.transform(write_t).or_else(write_err);
      }

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

  } // namespace parsing
} // namespace rfl

#endif