draconisplusplus/include/rfl/yaml/Reader.hpp

#ifndef RFL_YAML_READER_HPP_
#define RFL_YAML_READER_HPP_

#include <array>
#include <exception>
#include <map>
#include <memory>
#include <sstream>
#include <stdexcept>
#include <string>
#include <string_view>
#include <type_traits>
#include <unordered_map>
#include <vector>
#include <yaml-cpp/yaml.h>

#include "../Result.hpp"
#include "../always_false.hpp"

namespace rfl {
  namespace yaml {

    struct Reader {
      struct YAMLInputArray {
        YAMLInputArray(const YAML::Node& _node) : node_(_node) {}
        YAML::Node node_;
      };

      struct YAMLInputObject {
        YAMLInputObject(const YAML::Node& _node) : node_(_node) {}
        YAML::Node node_;
      };

      struct YAMLInputVar {
        YAMLInputVar(const YAML::Node& _node) : node_(_node) {}
        YAML::Node node_;
      };

      using InputArrayType  = YAMLInputArray;
      using InputObjectType = YAMLInputObject;
      using InputVarType    = YAMLInputVar;

      template <class T, class = void>
      struct has_from_json_obj : std::false_type {};

      template <class T>
      static constexpr bool has_custom_constructor =
        (requires(InputVarType var) { T::from_yaml_obj(var); });

      rfl::Result<InputVarType> get_field(const std::string& _name, const InputObjectType& _obj)
        const noexcept {
        auto var = InputVarType(_obj.node_[_name]);
        if (!var.node_) {
          return rfl::Error("Object contains no field named '" + _name + "'.");
        }
        return var;
      }

      bool is_empty(const InputVarType& _var) const noexcept { return !_var.node_ && true; }

      template <class T>
      rfl::Result<T> to_basic_type(const InputVarType& _var) const noexcept {
        try {
          if constexpr (std::is_same<std::remove_cvref_t<T>, std::string>() ||
                        std::is_same<std::remove_cvref_t<T>, bool>() ||
                        std::is_floating_point<std::remove_cvref_t<T>>() ||
                        std::is_integral<std::remove_cvref_t<T>>()) {
            return _var.node_.as<std::remove_cvref_t<T>>();
          } else {
            static_assert(rfl::always_false_v<T>, "Unsupported type.");
          }
        } catch (std::exception& e) { return rfl::Error(e.what()); }
      }

      rfl::Result<InputArrayType> to_array(const InputVarType& _var) const noexcept {
        if (!_var.node_.IsSequence()) {
          return rfl::Error("Could not cast to sequence!");
        }
        return InputArrayType(_var.node_);
      }

      template <class ArrayReader>
      std::optional<Error> read_array(const ArrayReader& _array_reader, const InputArrayType& _arr)
        const noexcept {
        for (size_t i = 0; i < _arr.node_.size(); ++i) {
          const auto err = _array_reader.read(_arr.node_[i]);
          if (err) {
            return err;
          }
        }
        return std::nullopt;
      }

      template <class ObjectReader>
      std::optional<Error>
      read_object(const ObjectReader& _object_reader, const InputObjectType& _obj) const noexcept {
        for (const auto& p : _obj.node_) {
          try {
            const auto k = p.first.as<std::string>();
            _object_reader.read(std::string_view(k), InputVarType(p.second));
          } catch (std::exception& e) { continue; }
        }
        return std::nullopt;
      }

      rfl::Result<InputObjectType> to_object(const InputVarType& _var) const noexcept {
        if (!_var.node_.IsMap()) {
          return rfl::Error("Could not cast to map!");
        }
        return InputObjectType(_var.node_);
      }

      template <class T>
      rfl::Result<T> use_custom_constructor(const InputVarType _var) const noexcept {
        try {
          return T::from_yaml_obj(_var);
        } catch (std::exception& e) { return rfl::Error(e.what()); }
      }
    };

  } // namespace yaml
} // namespace rfl

#endif