value_builder.hpp

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#pragma once
 
/// @file userver/formats/json/value_builder.hpp
/// @brief @copybrief formats::json::ValueBuilder
 
#include <chrono>
#include <string_view>
#include <type_traits>
 
#include <userver/formats/common/meta.hpp>
#include <userver/formats/common/transfer_tag.hpp>
#include <userver/formats/json/impl/mutable_value_wrapper.hpp>
#include <userver/formats/json/value.hpp>
#include <userver/utils/strong_typedef.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace formats::json {
 
// clang-format off
 
/// @ingroup userver_universal userver_containers userver_formats
///
/// @brief Builder for JSON.
///
/// Class provides methods for building JSON. For read only access to the
/// existing JSON values use formats::json::Value.
///
/// ## Example usage:
///
/// @snippet formats/json/value_builder_test.cpp  Sample formats::json::ValueBuilder usage
///
/// ## Customization example:
///
/// @snippet formats/json/value_builder_test.cpp  Sample Customization formats::json::ValueBuilder usage
///
/// @see @ref scripts/docs/en/userver/formats.md
 
// clang-format on
 
class ValueBuilder final {
public:
    struct IterTraits {
        using ValueType = formats::json::ValueBuilder;
        using Reference = formats::json::ValueBuilder&;
        using Pointer = formats::json::ValueBuilder*;
        using ContainerType = impl::MutableValueWrapper;
    };
 
    using iterator = Iterator<IterTraits>;
 
    /// Constructs a ValueBuilder that holds kNull
    ValueBuilder() = default;
 
    /// Constructs a valueBuilder that holds default value for provided `type`.
    ValueBuilder(formats::common::Type type);
 
    /// @brief Transfers the `ValueBuilder` object
    /// @see formats::common::TransferTag for the transfer semantics
    ValueBuilder(common::TransferTag, ValueBuilder&&) noexcept;
 
    ValueBuilder(const ValueBuilder& other);
    // NOLINTNEXTLINE(performance-noexcept-move-constructor)
    ValueBuilder(ValueBuilder&& other);
    ValueBuilder& operator=(const ValueBuilder& other);
    // NOLINTNEXTLINE(performance-noexcept-move-constructor)
    ValueBuilder& operator=(ValueBuilder&& other);
 
    ValueBuilder(const formats::json::Value& other);
    ValueBuilder(formats::json::Value&& other);
 
    /// @name Concrete type constructors
    /// @{
    ValueBuilder(std::nullptr_t)
        : ValueBuilder()
    {}
    ValueBuilder(bool t);
    ValueBuilder(const char* str);
    ValueBuilder(char* str);
    ValueBuilder(const std::string& str);
    ValueBuilder(std::string_view str);
    ValueBuilder(int t);
    ValueBuilder(unsigned int t);
    ValueBuilder(uint64_t t);
    ValueBuilder(int64_t t);
    ValueBuilder(float t);
    ValueBuilder(double t);
    /// @}
 
    /// Universal constructor using Serialize
    template <typename T>
    ValueBuilder(const T& t)
        : ValueBuilder(DoSerialize(t))
    {}
 
    /// @brief Access member by key for modification.
    /// @throw `TypeMismatchException` if not object or null value.
    ValueBuilder operator[](std::string key);
    /// @brief Access array member by index for modification.
    /// @throw `TypeMismatchException` if not an array value.
    /// @throw `OutOfBoundsException` if index is greater than size.
    ValueBuilder operator[](std::size_t index);
    /// @brief Access member by key for modification.
    /// @throw `TypeMismatchException` if not object or null value.
    template <typename Tag, utils::StrongTypedefOps Ops>
    requires(utils::IsStrongTypedefLoggable(Ops))
    ValueBuilder operator[](utils::StrongTypedef<Tag, std::string, Ops> key) {
        return (*this)[std::move(key.GetUnderlying())];
    }
 
    /// @brief Emplaces new member w/o a check whether the key already exists.
    /// @warning May create invalid JSON with duplicate key.
    /// @throw `TypeMismatchException` if not object or null value.
    void EmplaceNocheck(std::string_view key, ValueBuilder value);
 
    /// @brief Remove key from object. If key is missing nothing happens.
    /// @throw `TypeMismatchException` if value is not an object.
    void Remove(std::string_view key);
 
    iterator begin();
    iterator end();
 
    /// @brief Returns whether the array or object is empty.
    /// @throw `TypeMismatchException` if not an array or an object.
    bool IsEmpty() const;
 
    /// @brief Returns true if *this holds a Null (Type::kNull).
    bool IsNull() const noexcept;
 
    /// @brief Returns true if *this is convertible to bool.
    bool IsBool() const noexcept;
 
    /// @brief Returns true if *this is convertible to int.
    bool IsInt() const noexcept;
 
    /// @brief Returns true if *this is convertible to int64_t.
    bool IsInt64() const noexcept;
 
    /// @brief Returns true if *this is convertible to uint64_t.
    bool IsUInt64() const noexcept;
 
    /// @brief Returns true if *this is convertible to double.
    bool IsDouble() const noexcept;
 
    /// @brief Returns true if *this is convertible to std::string.
    bool IsString() const noexcept;
 
    /// @brief Returns true if *this is an array (Type::kArray).
    bool IsArray() const noexcept;
 
    /// @brief Returns true if *this holds a map (Type::kObject).
    bool IsObject() const noexcept;
 
    /// @brief Returns array size or object members count.
    /// @throw `TypeMismatchException` if not an array or an object.
    std::size_t GetSize() const;
 
    /// @brief Returns true if value holds a `key`.
    /// @throw `TypeMismatchException` if `*this` is not a map or null.
    bool HasMember(std::string_view key) const;
 
    /// @brief Returns full path to this value.
    std::string GetPath() const;
 
    /// @brief Resize the array value or convert null value
    /// into an array of requested size.
    /// @throw `TypeMismatchException` if not an array or null.
    void Resize(std::size_t size);
 
    /// @brief Add element into the last position of array.
    /// @throw `TypeMismatchException` if not an array or null.
    void PushBack(ValueBuilder&& bld);
 
    /// @brief Take out the resulting `Value` object.
    /// After calling this method the object is in unspecified
    /// (but valid - possibly null) state.
    /// @throw `json::Exception` if called not from the root builder.
    formats::json::Value ExtractValue();
 
private:
    class EmplaceEnabler {};
 
public:
    /// @cond
    ValueBuilder(EmplaceEnabler, impl::MutableValueWrapper) noexcept;
    /// @endcond
 
private:
    enum class CheckMemberExists { kYes, kNo };
 
    explicit ValueBuilder(impl::MutableValueWrapper) noexcept;
 
    static void Copy(impl::Value& to, const ValueBuilder& from);
    static void Move(impl::Value& to, ValueBuilder&& from);
 
    impl::Value& AddMember(std::string_view key, CheckMemberExists);
 
    template <typename T>
    static Value DoSerialize(const T& t);
 
    impl::MutableValueWrapper value_;
 
    friend class Iterator<IterTraits, common::IteratorDirection::kForward>;
    friend class Iterator<IterTraits, common::IteratorDirection::kReverse>;
};
 
template <typename T>
Value ValueBuilder::DoSerialize(const T& t) {
    static_assert(
        formats::common::impl::HasSerialize<Value, T>,
        "There is no `Serialize(const T&, formats::serialize::To<json::Value>)` "
        "in namespace of `T` or `formats::serialize`. "
        ""
        "Probably you forgot to include the <userver/formats/serialize/common_containers.hpp> header "
        "or one of the <formats/json/serialize_*.hpp> headers or you have not provided a `Serialize` function overload."
    );
 
    return Serialize(t, formats::serialize::To<Value>());
}
 
template <typename T>
requires(std::is_integral<T>::value && sizeof(T) <= sizeof(int64_t))
Value Serialize(T value, formats::serialize::To<Value>) {
    using Type = std::conditional_t<std::is_signed<T>::value, int64_t, uint64_t>;
    return json::ValueBuilder(static_cast<Type>(value)).ExtractValue();
}
 
json::Value Serialize(std::chrono::system_clock::time_point tp, formats::serialize::To<Value>);
 
/// Optimized maps of StrongTypedefs serialization for JSON
template <typename T>
requires(meta::kIsUniqueMap<T> && utils::IsStrongTypedefLoggable(T::key_type::kOps))
Value Serialize(const T& value, formats::serialize::To<Value>) {
    json::ValueBuilder builder(formats::common::Type::kObject);
    for (const auto& [key, value] : value) {
        builder.EmplaceNocheck(key.GetUnderlying(), value);
    }
    return builder.ExtractValue();
}
 
/// Optimized maps serialization for JSON
template <typename T>
requires meta::kIsUniqueMap<T> && std::is_convertible_v<typename T::key_type, std::string>
Value Serialize(const T& value, formats::serialize::To<Value>) {
    json::ValueBuilder builder(formats::common::Type::kObject);
    for (const auto& [key, value] : value) {
        builder.EmplaceNocheck(key, value);
    }
    return builder.ExtractValue();
}
 
}  // namespace formats::json
 
USERVER_NAMESPACE_END