draconisplusplus/include/rfl/internal/enums/StringConverter.hpp

#ifndef RFL_INTERNAL_ENUMS_STRINGCONVERTER_HPP_
#define RFL_INTERNAL_ENUMS_STRINGCONVERTER_HPP_

#include <algorithm>
#include <array>
#include <string>
#include <string_view>
#include <type_traits>

#include "../../Result.hpp"
#include "../../internal/strings/join.hpp"
#include "../../internal/strings/split.hpp"
#include "../../type_name_t.hpp"
#include "get_enum_names.hpp"
#include "is_flag_enum.hpp"

namespace rfl {
  namespace internal {
    namespace enums {

      template <class EnumType>
      class StringConverter {
       public:
        static constexpr bool is_flag_enum_ = is_flag_enum<EnumType>;

        static constexpr auto names_ =
            get_enum_names<EnumType, is_flag_enum_>();

        using NamesLiteral = typename decltype(names_)::Literal;

       public:
        /// Transform an enum to a matching string.
        static std::string enum_to_string(const EnumType _enum) {
          if constexpr (is_flag_enum_) {
            return flag_enum_to_string(_enum);
          } else {
            return enum_to_single_string(_enum);
          }
        }

        /// Transforms a string to the matching enum.
        static Result<EnumType> string_to_enum(const std::string& _str) {
          static_assert(
              names_.size != 0,
              "No enum could be identified. Please choose enum values "
              "between 0 to 127 or for flag enums choose 1,2,4,8,16,...");
          if constexpr (is_flag_enum_) {
            return string_to_flag_enum(_str);
          } else {
            return single_string_to_enum(_str);
          }
        }

       private:
        /// Iterates through the enum bit by bit and matches it against the
        /// flags.
        static std::string flag_enum_to_string(const EnumType _e) {
          using T  = std::underlying_type_t<EnumType>;
          auto val = static_cast<T>(_e);
          int i    = 0;
          std::vector<std::string> flags;
          while (val != 0) {
            const auto bit = val & static_cast<T>(1);
            if (bit == 1) {
              auto str = enum_to_single_string(
                  static_cast<EnumType>(static_cast<T>(1) << i));
              flags.emplace_back(std::move(str));
            }
            ++i;
            val >>= 1;
          }
          return strings::join("|", flags);
        }

        /// This assumes that _enum can be exactly matched to one of the names
        /// and does not have to be combined using |.
        static std::string enum_to_single_string(const EnumType _enum) {
          const auto to_str = [](const auto _l) { return _l.str(); };

          for (size_t i = 0; i < names_.size; ++i) {
            if (names_.enums_[i] == _enum) {
              return NamesLiteral::from_value(
                         static_cast<typename NamesLiteral::ValueType>(i))
                  .transform(to_str)
                  .value();
            }
          }

          return std::to_string(
              static_cast<std::underlying_type_t<EnumType>>(_enum));
        }

        /// Finds the enum matching the literal.
        static EnumType literal_to_enum(const NamesLiteral _lit) noexcept {
          return names_.enums_[_lit.value()];
        }

        /// This assumes that _enum can be exactly matched to one of the names
        /// and does not have to be combined using |.
        static Result<EnumType> single_string_to_enum(const std::string& _str) {
          const auto r =
              NamesLiteral::from_string(_str).transform(literal_to_enum);
          if (r) {
            return r;
          } else {
            try {
              return static_cast<EnumType>(std::stoi(_str));
            } catch (std::exception& exp) { return Error(exp.what()); }
          }
        }

        /// Only relevant if this is a flag enum - combines the different
        /// matches using |.
        static Result<EnumType> string_to_flag_enum(
            const std::string& _str) noexcept {
          using T          = std::underlying_type_t<EnumType>;
          const auto split = strings::split(_str, "|");
          auto res         = static_cast<T>(0);
          for (const auto& s : split) {
            const auto r = single_string_to_enum(s);
            if (r) {
              res |= static_cast<T>(*r);
            } else {
              return r;
            }
          }
          return static_cast<EnumType>(res);
        }
      };

    } // namespace enums
  } // namespace internal
} // namespace rfl

#endif