draconisplusplus/include/rfl/cbor/Reader.hpp

#ifndef RFL_CBOR_READER_HPP_
#define RFL_CBOR_READER_HPP_

#include <array>
#include <cbor.h>
#include <concepts>
#include <exception>
#include <map>
#include <memory>
#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 cbor {

    /// Please refer to https://intel.github.io/tinycbor/current/index.html
    struct Reader {
      struct CBORInputArray {
        CborValue* val_;
      };

      struct CBORInputObject {
        CborValue* val_;
      };

      struct CBORInputVar {
        CborValue* val_;
      };

      using InputArrayType  = CBORInputArray;
      using InputObjectType = CBORInputObject;
      using InputVarType    = CBORInputVar;

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

      rfl::Result<InputVarType> get_field(const std::string& _name, const InputObjectType& _obj)
        const noexcept {
        CborValue val;
        auto      buffer = std::vector<char>();
        auto      err    = cbor_value_enter_container(_obj.val_, &val);
        if (err != CborNoError) {
          return Error(cbor_error_string(err));
        }
        size_t length = 0;
        err           = cbor_value_get_map_length(_obj.val_, &length);
        if (err != CborNoError) {
          return Error(cbor_error_string(err));
        }
        for (size_t i = 0; i < length; ++i) {
          if (!cbor_value_is_text_string(&val)) {
            return Error("Expected the key to be a string value.");
          }
          err = get_string(&val, &buffer);
          if (err != CborNoError) {
            return Error(cbor_error_string(err));
          }
          err = cbor_value_advance(&val);
          if (err != CborNoError) {
            return Error(cbor_error_string(err));
          }
          if (_name == buffer.data()) {
            return to_input_var(&val);
          }
          err = cbor_value_advance(&val);
          if (err != CborNoError) {
            return Error(cbor_error_string(err));
          }
        }
        return Error("No field named '" + _name + "' was found.");
      }

      bool is_empty(const InputVarType& _var) const noexcept {
        return cbor_value_is_null(_var.val_);
      }

      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>()) {
          if (!cbor_value_is_text_string(_var.val_)) {
            return Error("Could not cast to string.");
          }
          std::vector<char> buffer;
          const auto        err = get_string(_var.val_, &buffer);
          if (err != CborNoError) {
            return Error(cbor_error_string(err));
          }
          return std::string(buffer.data());
        } else if constexpr (std::is_same<std::remove_cvref_t<T>, bool>()) {
          if (!cbor_value_is_boolean(_var.val_)) {
            return rfl::Error("Could not cast to boolean.");
          }
          bool       result = false;
          const auto err    = cbor_value_get_boolean(_var.val_, &result);
          if (err != CborNoError) {
            return Error(cbor_error_string(err));
          }
          return result;
        } else if constexpr (std::is_floating_point<std::remove_cvref_t<T>>() ||
                             std::is_integral<std::remove_cvref_t<T>>()) {
          if (cbor_value_is_integer(_var.val_)) {
            std::int64_t result = 0;
            const auto   err    = cbor_value_get_int64(_var.val_, &result);
            if (err != CborNoError) {
              return Error(cbor_error_string(err));
            }
            return static_cast<T>(result);
          } else if (cbor_value_is_float(_var.val_)) {
            float      result = 0.0;
            const auto err    = cbor_value_get_float(_var.val_, &result);
            if (err != CborNoError) {
              return Error(cbor_error_string(err));
            }
            return static_cast<T>(result);
          } else if (cbor_value_is_double(_var.val_)) {
            double     result = 0.0;
            const auto err    = cbor_value_get_double(_var.val_, &result);
            if (err != CborNoError) {
              return Error(cbor_error_string(err));
            }
            return static_cast<T>(result);
          }
          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 (!cbor_value_is_array(_var.val_)) {
          return Error("Could not cast to an array.");
        }
        return InputArrayType { _var.val_ };
      }

      rfl::Result<InputObjectType> to_object(const InputVarType& _var) const noexcept {
        if (!cbor_value_is_map(_var.val_)) {
          return Error("Could not cast to an object.");
        }
        return InputObjectType { _var.val_ };
      }

      template <class ArrayReader>
      std::optional<Error> read_array(const ArrayReader& _array_reader, const InputArrayType& _arr)
        const noexcept {
        CborValue val;
        auto      buffer = std::vector<char>();
        auto      err    = cbor_value_enter_container(_arr.val_, &val);
        if (err != CborNoError && err != CborErrorOutOfMemory) {
          return Error(cbor_error_string(err));
        }
        size_t length = 0;
        err           = cbor_value_get_array_length(_arr.val_, &length);
        if (err != CborNoError && err != CborErrorOutOfMemory) {
          return Error(cbor_error_string(err));
        }
        for (size_t i = 0; i < length; ++i) {
          const auto err2 = _array_reader.read(to_input_var(&val));
          if (err2) {
            return err2;
          }
          err = cbor_value_advance(&val);
          if (err != CborNoError && err != CborErrorOutOfMemory) {
            return Error(cbor_error_string(err));
          }
        }
        return std::nullopt;
      }

      template <class ObjectReader>
      std::optional<Error>
      read_object(const ObjectReader& _object_reader, const InputObjectType& _obj) const noexcept {
        size_t length = 0;
        auto   err    = cbor_value_get_map_length(_obj.val_, &length);
        if (err != CborNoError) {
          return Error(cbor_error_string(err));
        }

        CborValue val;
        err = cbor_value_enter_container(_obj.val_, &val);
        if (err != CborNoError) {
          return Error(cbor_error_string(err));
        }

        auto buffer = std::vector<char>();

        for (size_t i = 0; i < length; ++i) {
          err = get_string(&val, &buffer);
          if (err != CborNoError) {
            return Error(cbor_error_string(err));
          }
          err = cbor_value_advance(&val);
          if (err != CborNoError) {
            return Error(cbor_error_string(err));
          }
          const auto name = std::string_view(buffer.data(), buffer.size() - 1);
          _object_reader.read(name, InputVarType { &val });
          cbor_value_advance(&val);
        }

        return std::nullopt;
      }

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

     private:
      CborError get_string(const CborValue* _ptr, std::vector<char>* _buffer) const noexcept {
        size_t length = 0;
        auto   err    = cbor_value_get_string_length(_ptr, &length);
        if (err != CborNoError && err != CborErrorOutOfMemory) {
          return err;
        }
        _buffer->resize(length + 1);
        (*_buffer)[length] = '\0';
        return cbor_value_copy_text_string(_ptr, _buffer->data(), &length, NULL);
      }

      InputVarType to_input_var(CborValue* _ptr) const noexcept {
        values_->emplace_back(rfl::Box<CborValue>::make(*_ptr));
        auto* last_value = values_->back().get();
        return InputVarType { last_value };
      }

     private:
      /// Contains the values inside the object.
      rfl::Box<std::vector<rfl::Box<CborValue>>> values_;
    };

  } // namespace cbor
} // namespace rfl

#endif // JSON_PARSER_HPP_