draconisplusplus/include/rfl/msgpack/Reader.hpp

#ifndef RFL_MSGPACK_READER_HPP_
#define RFL_MSGPACK_READER_HPP_

#include <array>
#include <concepts>
#include <exception>
#include <map>
#include <memory>
#include <msgpack.h>
#include <source_location>
#include <sstream>
#include <stdexcept>
#include <string>
#include <string_view>
#include <type_traits>
#include <unordered_map>
#include <vector>

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

namespace rfl {
  namespace msgpack {

    struct Reader {
      using InputArrayType  = msgpack_object_array;
      using InputObjectType = msgpack_object_map;
      using InputVarType    = msgpack_object;

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

      rfl::Result<InputVarType> get_field(
          const std::string&     _name,
          const InputObjectType& _obj
      ) const noexcept {
        for (uint32_t i = 0; i < _obj.size; ++i) {
          const auto& key = _obj.ptr[i].key;
          if (key.type != MSGPACK_OBJECT_STR) {
            return Error(
                "Key in element " + std::to_string(i) + " was not a string."
            );
          }
          const auto current_name =
              std::string_view(key.via.str.ptr, key.via.str.size);
          if (_name == current_name) { return _obj.ptr[i].val; }
        }
        return Error("No field named '" + _name + "' was found.");
      }

      bool is_empty(const InputVarType& _var) const noexcept {
        return _var.type == MSGPACK_OBJECT_NIL;
      }

      template <class T>
      rfl::Result<T> to_basic_type(const InputVarType& _var) const noexcept {
        const auto type = _var.type;
        if constexpr (std::is_same<std::remove_cvref_t<T>, std::string>()) {
          if (type != MSGPACK_OBJECT_STR) {
            return Error("Could not cast to string.");
          }
          const auto str = _var.via.str;
          return std::string(str.ptr, str.size);
        } else if constexpr (std::is_same<std::remove_cvref_t<T>, bool>()) {
          if (type != MSGPACK_OBJECT_BOOLEAN) {
            return Error("Could not cast to boolean.");
          }
          return _var.via.boolean;
        } else if constexpr (std::is_floating_point<std::remove_cvref_t<T>>() ||
                             std::is_integral<std::remove_cvref_t<T>>()) {
          if (type == MSGPACK_OBJECT_FLOAT32 ||
              type == MSGPACK_OBJECT_FLOAT64 || type == MSGPACK_OBJECT_FLOAT) {
            return static_cast<T>(_var.via.f64);
          } else if (type == MSGPACK_OBJECT_POSITIVE_INTEGER) {
            return static_cast<T>(_var.via.u64);
          } else if (type == MSGPACK_OBJECT_NEGATIVE_INTEGER) {
            return static_cast<T>(_var.via.i64);
          }
          return rfl::Error(
              "Could not cast to numeric value. The type must be integral, "
              "float "
              "or double."
          );
        } else {
          static_assert(rfl::always_false_v<T>, "Unsupported type.");
        }
      }

      rfl::Result<InputArrayType> to_array(const InputVarType& _var
      ) const noexcept {
        if (_var.type != MSGPACK_OBJECT_ARRAY) {
          return Error("Could not cast to an array.");
        }
        return _var.via.array;
      }

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

      template <class ArrayReader>
      std::optional<Error> read_array(
          const ArrayReader&    _array_reader,
          const InputArrayType& _arr
      ) const noexcept {
        for (uint32_t i = 0; i < _arr.size; ++i) {
          const auto err = _array_reader.read(_arr.ptr[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 (uint32_t i = 0; i < _obj.size; ++i) {
          const auto& key = _obj.ptr[i].key;
          const auto& val = _obj.ptr[i].val;
          if (key.type != MSGPACK_OBJECT_STR) {
            return Error(
                "Key in element " + std::to_string(i) + " was not a string."
            );
          }
          const auto name = std::string_view(key.via.str.ptr, key.via.str.size);
          _object_reader.read(name, val);
        }
        return std::nullopt;
      }

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

  } // namespace msgpack
} // namespace rfl

#endif // JSON_PARSER_HPP_