draconisplusplus/include/rfl/toml/Reader.hpp

#ifndef RFL_TOML_READER_HPP_
#define RFL_TOML_READER_HPP_

#include <array>
#include <exception>
#include <map>
#include <memory>
#include <sstream>
#include <stdexcept>
#include <string>
#include <string_view>
#include <toml++/toml.hpp>
#include <type_traits>
#include <unordered_map>
#include <vector>

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

namespace rfl::toml {

  struct Reader {
    using InputArrayType  = ::toml::array*;
    using InputObjectType = ::toml::table*;
    using InputVarType    = ::toml::node*;

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

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

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

    template <class T>
    rfl::Result<T> to_basic_type(const InputVarType& _var) const noexcept {
      if constexpr (std::is_same<std::remove_cvref_t<T>, std::string>()) {
        const auto ptr = _var->as<std::string>();
        if (!ptr) {
          return Error("Could not cast the node to std::string!");
        }
        return **ptr;
      } else if constexpr (std::is_same<std::remove_cvref_t<T>, bool>()) {
        const auto ptr = _var->as<bool>();
        if (!ptr) {
          return Error("Could not cast the node to bool!");
        }
        return **ptr;
      } else if constexpr (std::is_floating_point<std::remove_cvref_t<T>>()) {
        const auto ptr = _var->as<double>();
        if (!ptr) {
          return Error("Could not cast the node to double!");
        }
        return static_cast<std::remove_cvref_t<T>>(**ptr);
      } else if constexpr (std::is_integral<std::remove_cvref_t<T>>()) {
        const auto ptr = _var->as<int64_t>();
        if (!ptr) {
          return Error("Could not cast the node to int64_t!");
        }
        return static_cast<std::remove_cvref_t<T>>(**ptr);
      } else {
        static_assert(rfl::always_false_v<T>, "Unsupported type.");
      }
    }

    rfl::Result<InputArrayType> to_array(const InputVarType& _var) const noexcept {
      const auto ptr = _var->as_array();
      if (!ptr) {
        return rfl::Error("Could not cast to an array!");
      }
      return ptr;
    }

    template <class ArrayReader>
    std::optional<Error> read_array(const ArrayReader& _array_reader, const InputArrayType& _arr)
      const noexcept {
      for (auto& node : *_arr) {
        const auto err = _array_reader.read(&node);
        if (err) {
          return err;
        }
      }
      return std::nullopt;
    }

    template <class ObjectReader>
    std::optional<Error> read_object(const ObjectReader& _object_reader, InputObjectType _obj)
      const noexcept {
      for (auto& [k, v] : *_obj) { _object_reader.read(std::string_view(k), &v); }
      return std::nullopt;
    }

    rfl::Result<InputObjectType> to_object(const InputVarType& _var) const noexcept {
      const auto ptr = _var->as_table();
      if (!ptr) {
        return rfl::Error("Could not cast to a table!");
      }
      return ptr;
    }

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

} // namespace rfl::toml

#endif