larra/library/include/larra/serialization.hpp

#pragma once
#include <libxml++/libxml++.h>
#include <spdlog/spdlog.h>

#include <nameof.hpp>
#include <string>
#include <utempl/utils.hpp>

namespace larra::xmpp {

template <typename T>
concept AsXml = requires(xmlpp::Element* element, const T& obj) {
  element << obj;
  { T::kDefaultName } -> std::convertible_to<const std::string&>;
};

template <typename T>
concept HasDefaultName = requires {
  { T::kDefaultName } -> std::convertible_to<const std::string&>;
};

template <typename T>
concept HasDefaultNamespace = requires {
  { T::kDefaultNamespace } -> std::convertible_to<const std::string&>;
};

template <typename T>
concept HasDefaultPrefix = requires {
  { T::kPrefix } -> std::convertible_to<const std::string&>;
};

template <typename T>
concept HasAddXmlDecl = requires {
  { T::kAddXmlDecl } -> std::convertible_to<bool>;
};

template <typename T>
concept HasRemoveEnd = requires {
  { T::kRemoveEnd } -> std::convertible_to<bool>;
};

template <typename T>
concept HasTryParse = requires(xmlpp::Element* element) {
  { T::TryParse(element) } -> std::same_as<std::optional<T>>;
};

template <typename T = void>
struct SerializationBase {
  inline static const std::string kDefaultName = [] {
    if constexpr(HasDefaultName<T>) {
      return T::kDefaultName;
    } else {
      return "";
    }
  }();
  inline static const std::string kDefaultNamespace = [] {
    if constexpr(HasDefaultNamespace<T>) {
      return T::kDefaultNamespace;
    } else {
      return "";
    }
  }();
  inline static const std::string kPrefix = [] {
    if constexpr(HasDefaultPrefix<T>) {
      return T::kPrefix;
    } else {
      return "";
    }
  }();
  static constexpr bool kAddXmlDecl = [] {
    if constexpr(HasAddXmlDecl<T>) {
      return T::kAddXmlDecl;
    } else {
      return false;
    }
  }();
  static constexpr bool kRemoveEnd = [] {
    if constexpr(HasRemoveEnd<T>) {
      return T::kRemoveEnd;
    } else {
      return false;
    }
  }();
  static constexpr auto StartCheck(xmlpp::Element* element) -> bool {
    if constexpr(requires {
                   { T::StartCheck(element) } -> std::same_as<bool>;
                 }) {
      return T::StartCheck(element);
    } else {
      return element && element->get_name() == kDefaultName;
    }
  };
};

template <typename T>
struct Serialization : SerializationBase<T> {
  [[nodiscard]] static constexpr auto Parse(xmlpp::Element* element) -> T {
    if(!Serialization::StartCheck(element)) {
      throw std::runtime_error("StartCheck failed");
    }
    return T::Parse(element);
  }
  [[nodiscard]] static constexpr auto TryParse(xmlpp::Element* element) -> std::optional<T> {
    if constexpr(HasTryParse<T>) {
      return Serialization::StartCheck(element) ? T::TryParse(element) : std::nullopt;
    } else {
      try {
        return Serialization::StartCheck(element) ? std::optional{T::Parse(element)} : std::nullopt;
      } catch(const std::exception& e) {
        SPDLOG_WARN("Type {}: Failed Parse but no TryParse found: {}", nameof::nameof_type<T>(), e.what());
      } catch(...) {
        SPDLOG_WARN("Type {}: Failed Parse but no TryParse found", nameof::nameof_type<T>());
      }
      return std::nullopt;
    }
  };
  static constexpr auto Serialize(xmlpp::Element* element, const T& object) -> void {
    element << object;
  }
};

template <typename T>
struct Serialization<std::optional<T>> : SerializationBase<T> {
  [[nodiscard]] static constexpr auto Parse(xmlpp::Element* element) -> std::optional<T> {
    return Serialization<T>::TryParse(element);
  }
  [[nodiscard]] static constexpr auto TryParse(xmlpp::Element* element) -> std::optional<std::optional<T>> {
    auto response = Serialization<T>::TryParse(element);
    return response ? *response : std::nullopt;
  }
  static constexpr auto Serialize(xmlpp::Element* element, const T& object) -> void {
    element << object;
  }
};

template <typename... Ts>
struct Serialization<std::variant<Ts...>> : SerializationBase<> {
  static constexpr auto StartCheck(xmlpp::Element* element) {
    return true;
  }

 private:
  template <typename T>
  static constexpr auto FunctionForType(xmlpp::Element* element) {
    return [=] -> std::optional<T> {
      if(Serialization<T>::StartCheck(element)) {
        return Serialization<T>::TryParse(element);
      } else {
        SPDLOG_DEBUG("StartCheck failed for type {}", nameof::nameof_type<T>());
        return std::nullopt;
      }
    };
  }

 public:
  [[nodiscard]] static constexpr auto TryParse(xmlpp::Element* element) -> std::optional<std::variant<Ts...>> {
    return utempl::FirstOf(utempl::Tuple{FunctionForType<Ts>(element)...}, std::optional<std::variant<Ts...>>{});
  }
  [[nodiscard]] static constexpr auto Parse(xmlpp::Element* element) {
    return [&]<typename... TTs>(utempl::TypeList<TTs...>) {
      // operator* is safe because in or_else Parse returns Ts...[sizeof...(Ts) - 1] (not optional)
      return *utempl::FirstOf(utempl::Tuple{FunctionForType<TTs>(element)...}, std::optional<std::variant<Ts...>>{})
                  .or_else([&] -> std::optional<std::variant<Ts...>> {
                    return Serialization<decltype(utempl::Get<sizeof...(Ts) - 1>(utempl::kTypeList<Ts...>))>::Parse(element);
                  });
    }(utempl::TakeFrom<sizeof...(Ts) - 1>(utempl::kTypeList<Ts...>));
  }
  static constexpr auto Serialize(xmlpp::Element* element, const std::variant<Ts...>& object) -> void {
    std::visit(
        [&](const auto& object) {
          element << object;
        },
        object);
  }
};

template <>
struct Serialization<std::monostate> : SerializationBase<> {
  static constexpr auto StartCheck(xmlpp::Element*) -> bool {
    return true;
  };
  [[nodiscard]] static constexpr auto TryParse(xmlpp::Element*) -> std::optional<std::monostate> {
    return std::monostate{};
  }
  [[nodiscard]] static constexpr auto Parse(xmlpp::Element*) -> std::monostate {
    return {};
  }
  static constexpr auto Serialize(xmlpp::Element*, const std::monostate&) -> void {
  }
};

}  // namespace larra::xmpp