value.hpp

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#pragma once
 
/// @file userver/formats/bson/value.hpp
/// @brief @copybrief formats::bson::Value
 
#include <chrono>
#include <cstddef>
#include <cstdint>
#include <string>
 
#include <userver/formats/bson/exception.hpp>
#include <userver/formats/bson/iterator.hpp>
#include <userver/formats/bson/types.hpp>
#include <userver/formats/common/items.hpp>
#include <userver/formats/common/meta.hpp>
#include <userver/formats/parse/common.hpp>
#include <userver/formats/parse/common_containers.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace formats::bson {
namespace impl {
class BsonBuilder;
class ValueImpl;
}  // namespace impl
 
class Document;
class ValueBuilder;
 
/// @brief Non-mutable BSON value representation.
///
/// Class provides non mutable access BSON value. For modification and
/// construction of new BSON values use formats::bson::ValueBuilder.
///
/// ## Example usage:
///
/// @snippet formats/bson/value_test.cpp  Sample formats::bson::Value usage
///
/// @see @ref scripts/docs/en/userver/formats.md
///
/// To iterate over `Value` as object use formats::common::Items.
class Value {
public:
    struct DefaultConstructed {};
 
    using const_iterator = Iterator<const Value, common::IteratorDirection::kForward>;
    using const_reverse_iterator = Iterator<const Value, common::IteratorDirection::kReverse>;
    using Exception = formats::bson::BsonException;
    using ParseException = formats::bson::ParseException;
    using ExceptionWithPath = formats::bson::ExceptionWithPath;
    using Builder = ValueBuilder;
 
    /// @brief Selectors for duplicate fields parsing behavior
    /// @see SetDuplicateFieldsPolicy
    enum class DuplicateFieldsPolicy { kForbid, kUseFirst, kUseLast };
 
    /// Constructs a `null` value
    Value();
 
    Value(const Value&) = default;
    Value(Value&&) noexcept = default;
    Value& operator=(const Value&) & = default;
    Value& operator=(Value&&) & noexcept = default;
 
    template <class T>
    Value& operator=(T&&) && {
        static_assert(
            !sizeof(T),
            "You're assigning to a temporary formats::bson::Value! Use "
            "formats::bson::ValueBuilder for data modifications."
        );
        return *this;
    }
 
    /// @cond
    /// Constructor from implementation, internal use only
    explicit Value(impl::ValueImplPtr);
    /// @endcond
 
    /// @brief Retrieves document field by name
    /// @param name field name
    /// @throws TypeMismatchException if value is not a missing value, a document,
    /// or `null`
    Value operator[](const std::string& name) const;
 
    /// @brief Retrieves array element by index
    /// @param index element index
    /// @throws TypeMismatchException if value is not an array or `null`
    /// @throws OutOfBoundsException if index is invalid for the array
    Value operator[](uint32_t index) const;
 
    /// @brief Checks whether the document has a field
    /// @param name field name
    /// @throws TypeMismatchExcepiton if value is not a document or `null`
    bool HasMember(const std::string& name) const;
 
    /// @brief Returns an iterator to the first array element/document field
    /// @throws TypeMismatchException if value is not a document, array or `null`
    ///
    /// To iterate over `Value` as object use formats::common::Items.
    const_iterator begin() const;
 
    /// @brief Returns an iterator following the last array element/document field
    /// @throws TypeMismatchException if value is not a document, array or `null`
    const_iterator end() const;
 
    /// @brief Returns a reversed iterator to the last array element
    /// @throws TypeMismatchException if value is not an array or `null`
    const_reverse_iterator rbegin() const;
 
    /// @brief Returns a reversed iterator following the first array element
    /// @throws TypeMismatchException if value is not an array or `null`
    const_reverse_iterator rend() const;
 
    /// @brief Returns whether the document/array is empty
    /// @throws TypeMismatchException if value is not a document, array or `null`
    /// @note Returns `true` for `null`.
    bool IsEmpty() const;
 
    /// @brief Returns the number of elements in a document/array
    /// @throws TypeMismatchException if value is not a document, array or `null`
    /// @note May require linear time before the first element access.
    /// @note Returns 0 for `null`.
    uint32_t GetSize() const;
 
    /// Returns value path in a document
    std::string GetPath() const;
 
    bool operator==(const Value&) const;
 
    /// @brief Checks whether the selected element exists
    /// @note MemberMissingException is throws on nonexisting element access
    bool IsMissing() const;
 
    /// @name Type checking
    /// @{
    bool IsArray() const;
    bool IsDocument() const;
    bool IsNull() const;
    bool IsBool() const;
    bool IsInt() const;
    bool IsInt32() const;
    bool IsInt64() const;
    bool IsUInt64() const;
    bool IsDouble() const;
    bool IsString() const;
    bool IsDateTime() const;
    bool IsOid() const;
    bool IsBinary() const;
    bool IsDecimal128() const;
    bool IsMinKey() const;
    bool IsMaxKey() const;
    bool IsTimestamp() const;
 
    bool IsObject() const { return IsDocument(); }
    /// @}
 
    /// Extracts the specified type with strict type checks
    ///
    /// ## Example usage:
    ///
    /// @snippet formats/bson/value_test.cpp  Sample formats::bson::Value::As<T>() usage
    ///
    /// @see @ref scripts/docs/en/userver/formats.md
    template <typename T>
    auto As() const {
        static_assert(
            formats::common::impl::HasParse<Value, T>,
            "There is no `Parse(const Value&, formats::parse::To<T>)` in namespace "
            "of `T` or `formats::parse`. "
            "Probably you have not provided a `Parse` function overload."
        );
 
        return Parse(*this, formats::parse::To<T>{});
    }
 
    /// Extracts the specified type with strict type checks, or constructs the
    /// default value when the field is not present
    template <typename T, typename First, typename... Rest>
    auto As(First&& default_arg, Rest&&... more_default_args) const {
        if (IsMissing() || IsNull()) {
            // intended raw ctor call, sometimes casts
            // NOLINTNEXTLINE(google-readability-casting)
            return decltype(As<T>())(std::forward<First>(default_arg), std::forward<Rest>(more_default_args)...);
        }
        return As<T>();
    }
 
    /// @brief Returns value of *this converted to T or T() if this->IsMissing().
    /// @throw Anything derived from std::exception.
    /// @note Use as `value.As<T>({})`
    template <typename T>
    auto As(DefaultConstructed) const {
        return (IsMissing() || IsNull()) ? decltype(As<T>())() : As<T>();
    }
 
    /// @brief Extracts the specified type with relaxed type checks.
    /// For example, `true` may be converted to 1.0.
    template <typename T>
    T ConvertTo() const {
        if constexpr (formats::common::impl::HasConvert<Value, T>) {
            return Convert(*this, formats::parse::To<T>{});
        } else if constexpr (formats::common::impl::HasParse<Value, T>) {
            return Parse(*this, formats::parse::To<T>{});
        } else {
            static_assert(
                !sizeof(T),
                "There is no `Convert(const Value&, formats::parse::To<T>)` or "
                "`Parse(const Value&, formats::parse::To<T>)` in namespace of `T` or `formats::parse`. "
                "Probably you have not provided a `Convert` function overload."
            );
        }
    }
 
    /// Extracts the specified type with strict type checks, or constructs the
    /// default value when the field is not present
    template <typename T, typename First, typename... Rest>
    T ConvertTo(First&& default_arg, Rest&&... more_default_args) const {
        if (IsMissing() || IsNull()) {
            // NOLINTNEXTLINE(google-readability-casting)
            return T(std::forward<First>(default_arg), std::forward<Rest>(more_default_args)...);
        }
        return ConvertTo<T>();
    }
 
    /// @brief Changes parsing behavior when duplicate fields are encountered.
    /// Should not be used normally.
    /// @details Should be called before the first field access. Only affects
    /// documents. Default policy is to throw an exception when duplicate fields
    /// are encountered.
    /// @warning At most one value will be read, all others will be discarded and
    /// cannot be serialized back!
    void SetDuplicateFieldsPolicy(DuplicateFieldsPolicy);
 
    /// Throws a MemberMissingException if the selected element does not exist
    void CheckNotMissing() const;
 
    /// @brief Throws a TypeMismatchException if the selected element
    /// is not an array or null
    void CheckArrayOrNull() const;
 
    /// @brief Throws a TypeMismatchException if the selected element
    /// is not a document or null
    void CheckDocumentOrNull() const;
 
    /// @cond
    /// Same, for parsing capabilities
    void CheckObjectOrNull() const { CheckDocumentOrNull(); }
 
    /// @brief Returns an array as its internal representation (BSON document),
    /// internal use only
    Document GetInternalArrayDocument() const;
    /// @endcond
 
protected:
    const impl::BsonHolder& GetBson() const;
 
private:
    friend class ValueBuilder;
    friend class impl::BsonBuilder;
 
    friend bool Parse(const Value& value, parse::To<bool>);
    friend int64_t Parse(const Value& value, parse::To<int64_t>);
    friend uint64_t Parse(const Value& value, parse::To<uint64_t>);
    friend double Parse(const Value& value, parse::To<double>);
    friend std::string Parse(const Value& value, parse::To<std::string>);
    friend std::chrono::system_clock::time_point
    Parse(const Value& value, parse::To<std::chrono::system_clock::time_point>);
    friend Oid Parse(const Value& value, parse::To<Oid>);
    friend Binary Parse(const Value& value, parse::To<Binary>);
    friend Decimal128 Parse(const Value& value, parse::To<Decimal128>);
    friend Timestamp Parse(const Value& value, parse::To<Timestamp>);
    friend Document Parse(const Value& value, parse::To<Document>);
 
    impl::ValueImplPtr impl_;
};
 
/// @cond
bool Parse(const Value& value, parse::To<bool>);
 
int64_t Parse(const Value& value, parse::To<int64_t>);
 
uint64_t Parse(const Value& value, parse::To<uint64_t>);
 
double Parse(const Value& value, parse::To<double>);
 
std::string Parse(const Value& value, parse::To<std::string>);
 
std::chrono::system_clock::time_point Parse(const Value& value, parse::To<std::chrono::system_clock::time_point>);
 
Oid Parse(const Value& value, parse::To<Oid>);
 
Binary Parse(const Value& value, parse::To<Binary>);
 
Decimal128 Parse(const Value& value, parse::To<Decimal128>);
 
Timestamp Parse(const Value& value, parse::To<Timestamp>);
 
Document Parse(const Value& value, parse::To<Document>);
 
template <>
bool Value::ConvertTo<bool>() const;
 
template <>
int64_t Value::ConvertTo<int64_t>() const;
 
template <>
uint64_t Value::ConvertTo<uint64_t>() const;
 
template <>
double Value::ConvertTo<double>() const;
 
template <>
std::string Value::ConvertTo<std::string>() const;
/// @endcond
 
/// @brief Wrapper for handy python-like iteration over a map
///
/// @code
///   for (const auto& [name, value]: Items(map)) ...
/// @endcode
using formats::common::Items;
 
}  // namespace formats::bson
 
/// Although we provide user defined literals, please beware that
/// 'using namespace ABC' may contradict code style of your company.
namespace formats::literals {
 
bson::Value operator""_bson(const char* str, std::size_t len);
 
}  // namespace formats::literals
 
USERVER_NAMESPACE_END