draconisplusplus/include/rfl/bson/Writer.hpp

#ifndef RFL_BSON_WRITER_HPP_
#define RFL_BSON_WRITER_HPP_

#include <bson/bson.h>
#include <exception>
#include <map>
#include <sstream>
#include <stdexcept>
#include <string>
#include <string_view>
#include <type_traits>
#include <variant>
#include <vector>

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

namespace rfl {
  namespace bson {

    /// Please refer to https://mongoc.org/libbson/current/api.html
    class Writer {
      struct BSONType {
        bson_t val_;
      };

      struct IsArray {
        bson_array_builder_t* ptr_;
      };

      struct IsObject {
        bson_t* ptr_;
      };

      struct IsRoot {};

      using ParentType = std::variant<IsArray, IsObject, IsRoot>;

     public:
      struct BSONOutputArray {
        BSONOutputArray(bson_array_builder_t* _val, ParentType _parent)
            : parent_(_parent), val_(_val) {}
        ParentType            parent_;
        bson_array_builder_t* val_;
      };

      struct BSONOutputObject {
        BSONOutputObject(bson_t* _val, ParentType _parent)
            : parent_(_parent), val_(_val) {}
        ParentType parent_;
        bson_t*    val_;
      };

      struct BSONOutputVar {};

      using OutputArrayType  = BSONOutputArray;
      using OutputObjectType = BSONOutputObject;
      using OutputVarType    = BSONOutputVar;

      Writer(bson_t* _doc) : doc_(_doc) {}

      ~Writer() = default;

      OutputArrayType array_as_root(const size_t _size) const noexcept {
        bson_array_builder_t* val = bson_array_builder_new();
        return OutputArrayType(val, IsRoot {});
      }

      OutputObjectType object_as_root(const size_t _size) const noexcept {
        return OutputObjectType(doc_, IsRoot {});
      }

      OutputVarType null_as_root() const noexcept {
        // Appears to be unsupported by the BSON C API.
        return OutputVarType {};
      }

      template <class T>
      OutputVarType value_as_root(const T& _var) const noexcept {
        static_assert(
            rfl::always_false_v<T>,
            "BSON only allows arrays or objects as its root."
        );
        return OutputVarType {};
      }

      OutputArrayType add_array_to_array(
          const size_t     _size,
          OutputArrayType* _parent
      ) const noexcept {
        bson_array_builder_t* val;
        bson_array_builder_append_array_builder_begin(_parent->val_, &val);
        return OutputArrayType(val, IsArray {_parent->val_});
      }

      OutputArrayType add_array_to_object(
          const std::string_view& _name,
          const size_t            _size,
          OutputObjectType*       _parent
      ) const noexcept {
        bson_array_builder_t* val;
        bson_append_array_builder_begin(
            _parent->val_, _name.data(), static_cast<int>(_name.size()), &val
        );
        return OutputArrayType(val, IsObject {_parent->val_});
      }

      OutputObjectType add_object_to_array(
          const size_t     _size,
          OutputArrayType* _parent
      ) const noexcept {
        subdocs_->emplace_back(rfl::Box<BSONType>());
        bson_array_builder_append_document_begin(
            _parent->val_, &(subdocs_->back()->val_)
        );
        return OutputObjectType(
            &subdocs_->back()->val_, IsArray {_parent->val_}
        );
      }

      OutputObjectType add_object_to_object(
          const std::string_view& _name,
          const size_t            _size,
          OutputObjectType*       _parent
      ) const noexcept {
        subdocs_->emplace_back(rfl::Box<BSONType>());
        bson_append_document_begin(
            _parent->val_,
            _name.data(),
            static_cast<int>(_name.size()),
            &(subdocs_->back()->val_)
        );
        return OutputObjectType(
            &subdocs_->back()->val_, IsObject {_parent->val_}
        );
      }

      template <class T>
      OutputVarType add_value_to_array(const T& _var, OutputArrayType* _parent)
          const noexcept {
        if constexpr (std::is_same<std::remove_cvref_t<T>, std::string>()) {
          bson_array_builder_append_utf8(
              _parent->val_, _var.c_str(), static_cast<int>(_var.size())
          );
        } else if constexpr (std::is_same<std::remove_cvref_t<T>, bool>()) {
          bson_array_builder_append_bool(_parent->val_, _var);
        } else if constexpr (std::is_floating_point<std::remove_cvref_t<T>>()) {
          bson_array_builder_append_double(
              _parent->val_, static_cast<double>(_var)
          );
        } else if constexpr (std::is_integral<std::remove_cvref_t<T>>()) {
          bson_array_builder_append_int64(
              _parent->val_, static_cast<std::int64_t>(_var)
          );
        } else if constexpr (std::is_same<std::remove_cvref_t<T>, bson_oid_t>(
                             )) {
          bson_array_builder_append_oid(_parent->val_, &_var);
        } else {
          static_assert(rfl::always_false_v<T>, "Unsupported type.");
        }
        return OutputVarType {};
      }

      template <class T>
      OutputVarType add_value_to_object(
          const std::string_view& _name,
          const T&                _var,
          OutputObjectType*       _parent
      ) const noexcept {
        if constexpr (std::is_same<std::remove_cvref_t<T>, std::string>()) {
          bson_append_utf8(
              _parent->val_,
              _name.data(),
              static_cast<int>(_name.size()),
              _var.c_str(),
              static_cast<int>(_var.size())
          );
        } else if constexpr (std::is_same<std::remove_cvref_t<T>, bool>()) {
          bson_append_bool(
              _parent->val_, _name.data(), static_cast<int>(_name.size()), _var
          );
        } else if constexpr (std::is_floating_point<std::remove_cvref_t<T>>()) {
          bson_append_double(
              _parent->val_,
              _name.data(),
              static_cast<int>(_name.size()),
              static_cast<double>(_var)
          );
        } else if constexpr (std::is_integral<std::remove_cvref_t<T>>()) {
          bson_append_int64(
              _parent->val_,
              _name.data(),
              static_cast<int>(_name.size()),
              static_cast<std::int64_t>(_var)
          );
        } else if constexpr (std::is_same<std::remove_cvref_t<T>, bson_oid_t>(
                             )) {
          bson_append_oid(
              _parent->val_, _name.data(), static_cast<int>(_name.size()), &_var
          );
        } else {
          static_assert(rfl::always_false_v<T>, "Unsupported type.");
        }
        return OutputVarType {};
      }

      OutputVarType add_null_to_array(OutputArrayType* _parent) const noexcept {
        bson_array_builder_append_null(_parent->val_);
        return OutputVarType {};
      }

      OutputVarType add_null_to_object(
          const std::string_view& _name,
          OutputObjectType*       _parent
      ) const noexcept {
        bson_append_null(
            _parent->val_, _name.data(), static_cast<int>(_name.size())
        );
        return OutputVarType {};
      }

      void end_array(OutputArrayType* _arr) const noexcept {
        const auto handle = [&](const auto _parent) {
          using Type = std::remove_cvref_t<decltype(_parent)>;
          if constexpr (std::is_same<Type, IsArray>()) {
            bson_array_builder_append_array_builder_end(
                _parent.ptr_, _arr->val_
            );
          } else if constexpr (std::is_same<Type, IsObject>()) {
            bson_append_array_builder_end(_parent.ptr_, _arr->val_);
          } else if constexpr (std::is_same<Type, IsRoot>()) {
            bson_array_builder_build(_arr->val_, doc_);
          } else {
            static_assert(rfl::always_false_v<Type>, "Unsupported type.");
          }
        };
        std::visit(handle, _arr->parent_);
      }

      void end_object(OutputObjectType* _obj) const noexcept {
        const auto handle = [&](const auto _parent) {
          using Type = std::remove_cvref_t<decltype(_parent)>;
          if constexpr (std::is_same<Type, IsArray>()) {
            bson_array_builder_append_document_end(_parent.ptr_, _obj->val_);
          } else if constexpr (std::is_same<Type, IsObject>()) {
            bson_append_document_end(_parent.ptr_, _obj->val_);
          } else if constexpr (std::is_same<Type, IsRoot>()) {
          } else {
            static_assert(rfl::always_false_v<Type>, "Unsupported type.");
          }
        };
        std::visit(handle, _obj->parent_);
      }

     private:
      /// Pointer to the main document. In BSON, documents are what are usually
      /// called objects.
      bson_t* const doc_;

      /// Contain all of the subdocuments.
      const rfl::Ref<std::vector<rfl::Box<BSONType>>> subdocs_;
    };

  } // namespace bson
} // namespace rfl

#endif // BSON_PARSER_HPP_