libconfig/build-config/reflect-cpp/include/rfl/parsing/ViewReader.hpp

#ifndef RFL_PARSING_VIEWREADER_HPP_
#define RFL_PARSING_VIEWREADER_HPP_

#include <array>
#include <sstream>
#include <string_view>
#include <type_traits>
#include <utility>
#include <vector>

#include "../Result.hpp"
#include "../Tuple.hpp"
#include "../internal/is_array.hpp"
#include "Parser_base.hpp"
#include "schemaful/IsSchemafulReader.hpp"

namespace rfl::parsing {

template <class R, class W, class ViewType, class ProcessorsType>
class ViewReader {
 private:
  using InputVarType = typename R::InputVarType;
  static constexpr size_t size_ = ViewType::size();

 public:
  ViewReader(const R* _r, ViewType* _view, std::array<bool, size_>* _found,
             std::array<bool, size_>* _set, std::vector<Error>* _errors)
      : r_(_r), view_(_view), found_(_found), set_(_set), errors_(_errors) {}

  ~ViewReader() = default;

  /// Assigns the parsed version of _var to the field signified by _name, if
  /// such a field exists in the underlying view.
  void read(const std::string_view& _name, const InputVarType& _var) const {
    assign_to_matching_field(*r_, _name, _var, view_, errors_, found_, set_,
                             std::make_integer_sequence<int, size_>());
  }

  /// Assigns the parsed version of _var to the field signified by _index, if
  /// such a field exists in the underlying view.
  /// Note that schemaful formats can assign by index.
  void read(const int _index, const InputVarType& _var) const {
    assign_to_matching_field(*r_, _index, _var, view_, errors_, found_, set_,
                             std::make_integer_sequence<int, size_>());
  }

 private:
  template <int i, class FieldType>
  static bool is_matching(const int _current_index) {
    return _current_index == i;
  }

  template <int i, class FieldType>
  static bool is_matching(const std::string_view& _current_name) {
    return _current_name == FieldType::name();
  }

  template <int i>
  static void assign_if_field_matches(const R& _r,
                                      const auto _current_name_or_index,
                                      const auto& _var, auto* _view,
                                      auto* _errors, auto* _found, auto* _set,
                                      bool* _already_assigned) {
    using FieldType = tuple_element_t<i, typename ViewType::Fields>;
    using OriginalType = typename FieldType::Type;
    using T =
        std::remove_cvref_t<std::remove_pointer_t<typename FieldType::Type>>;
    constexpr auto name = FieldType::name();
    if (!(*_already_assigned) && !std::get<i>(*_found) &&
        is_matching<i, FieldType>(_current_name_or_index)) {
      std::get<i>(*_found) = true;
      *_already_assigned = true;
      auto res = Parser<R, W, T, ProcessorsType>::read(_r, _var);
      if (!res) {
        std::stringstream stream;
        stream << "Failed to parse field '" << std::string(name)
               << "': " << res.error().what();
        _errors->emplace_back(Error(stream.str()));
        return;
      }
      if constexpr (std::is_pointer_v<OriginalType>) {
        move_to(rfl::get<i>(*_view), &(*res));
      } else {
        rfl::get<i>(*_view) = std::move(*res);
      }
      std::get<i>(*_set) = true;
    }
  }

  template <int _pos>
  static void assign_to_extra_fields(const R& _r,
                                     const std::string_view& _current_name,
                                     const auto& _var, auto* _view,
                                     auto* _errors, auto* _found, auto* _set) {
    auto* extra_fields = _view->template get<_pos>();
    using ExtraFieldsType =
        std::remove_cvref_t<std::remove_pointer_t<decltype(extra_fields)>>;
    using T = std::remove_cvref_t<
        std::remove_pointer_t<typename ExtraFieldsType::Type>>;
    if (!std::get<_pos>(*_set)) {
      ::new (extra_fields) ExtraFieldsType();
      std::get<_pos>(*_set) = true;
      std::get<_pos>(*_found) = true;
    }
    auto res = Parser<R, W, T, ProcessorsType>::read(_r, _var);
    if (!res) {
      std::stringstream stream;
      stream << "Failed to parse field '" << _current_name
             << "': " << res.error().what();
      _errors->emplace_back(Error(stream.str()));
      return;
    }
    extra_fields->emplace(std::string(_current_name), std::move(*res));
  }

  template <int... is>
  static void assign_to_matching_field(const R& _r,
                                       const auto _current_name_or_index,
                                       const auto& _var, auto* _view,
                                       auto* _errors, auto* _found, auto* _set,
                                       std::integer_sequence<int, is...>) {
    bool already_assigned = false;

    (assign_if_field_matches<is>(_r, _current_name_or_index, _var, _view,
                                 _errors, _found, _set, &already_assigned),
     ...);

    if constexpr (ViewType::pos_extra_fields() != -1) {
      static_assert(!schemaful::IsSchemafulReader<R>,
                    "rfl::ExtraFields are not supported for schemaful formats, "
                    "because schemaful formats cannot have extra fields.");
      constexpr int pos = ViewType::pos_extra_fields();
      if (!already_assigned) {
        assign_to_extra_fields<pos>(_r, _current_name_or_index, _var, _view,
                                    _errors, _found, _set);
      }
    } else if constexpr (ProcessorsType::no_extra_fields_) {
      static_assert(
          !schemaful::IsSchemafulReader<R>,
          "Passing rfl::NoExtraFields to a schemaful format does not make "
          "sense, because schemaful formats cannot have extra fields.");
      if (!already_assigned) {
        std::stringstream stream;
        stream << "Value named '" << _current_name_or_index
               << "' not used. Remove the rfl::NoExtraFields processor or add "
                  "rfl::ExtraFields to avoid this error message.";
        _errors->emplace_back(Error(stream.str()));
      }
    }
  }

  template <class Target, class Source>
  static void move_to(Target* _t, Source* _s) {
    if constexpr (std::is_const_v<Target>) {
      return move_to(const_cast<std::remove_const_t<Target>*>(_t), _s);
    } else if constexpr (!rfl::internal::is_array_v<Source> &&
                         !std::is_array_v<Target>) {
      ::new (_t) Target(std::move(*_s));
    } else if constexpr (rfl::internal::is_array_v<Source>) {
      static_assert(std::is_array_v<Target>,
                    "Expected target to be a c-array.");
      for (size_t i = 0; i < _s->arr_.size(); ++i) {
        move_to(&((*_t)[i]), &(_s->arr_[i]));
      }
    } else {
      for (size_t i = 0; i < _s->size(); ++i) {
        move_to(&((*_t)[i]), &((*_s)[i]));
      }
    }
  }

 private:
  /// The underlying reader.
  const R* r_;

  /// The underlying view.
  ViewType* view_;

  /// Indicates that a certain field has been found.
  std::array<bool, size_>* found_;

  /// Indicates that a certain field has been successfully set - necessary,
  /// because we have to trigger the destructors manually.
  std::array<bool, size_>* set_;

  /// Collects any errors we may have come across.
  std::vector<Error>* errors_;
};

}  // namespace rfl::parsing

#endif