ClickHouse/src/Functions/DummyJSONParser.h

#pragma once

#include <Common/Exception.h>
#include <base/types.h>

namespace DB
{
namespace ErrorCodes
{
    extern const int NOT_IMPLEMENTED;
}

/// This class can be used as an argument for the template class FunctionJSON when we unable to parse JSONs.
/// It can't do anything useful and just throws an exception.
struct DummyJSONParser
{
    class Array;
    class Object;

    /// References an element in a JSON document, representing a JSON null, boolean, string, number,
    /// array or object.
    class Element
    {
    public:
        Element() {}
        bool isInt64() const { return false; }
        bool isUInt64() const { return false; }
        bool isDouble() const { return false; }
        bool isString() const { return false; }
        bool isArray() const { return false; }
        bool isObject() const { return false; }
        bool isBool() const { return false; }
        bool isNull() const { return false; }

        Int64 getInt64() const { return 0; }
        UInt64 getUInt64() const { return 0; }
        double getDouble() const { return 0; }
        bool getBool() const { return false; }
        std::string_view getString() const { return {}; }
        Array getArray() const { return {}; }
        Object getObject() const { return {}; }

        Element getElement() { return {}; }
    };

    /// References an array in a JSON document.
    class Array
    {
    public:
        class Iterator
        {
        public:
            Element operator*() const { return {}; }
            Iterator & operator++() { return *this; }
            Iterator operator++(int) { return *this; }
            friend bool operator==(const Iterator &, const Iterator &) { return true; }
            friend bool operator!=(const Iterator &, const Iterator &) { return false; }
        };

        Iterator begin() const { return {}; }
        Iterator end() const { return {}; }
        size_t size() const { return 0; }
        Element operator[](size_t) const { return {}; }
    };

    using KeyValuePair = std::pair<std::string_view, Element>;

    /// References an object in a JSON document.
    class Object
    {
    public:
        class Iterator
        {
        public:
            KeyValuePair operator*() const { return {}; }
            Iterator & operator++() { return *this; }
            Iterator operator++(int) { return *this; }
            friend bool operator==(const Iterator &, const Iterator &) { return true; }
            friend bool operator!=(const Iterator &, const Iterator &) { return false; }
        };

        Iterator begin() const { return {}; }
        Iterator end() const { return {}; }
        size_t size() const { return 0; }
        bool find(const std::string_view &, Element &) const { return false; }

#if 0
        /// Optional: Provides access to an object's element by index.
        KeyValuePair operator[](size_t) const { return {}; }
#endif
    };

    /// Parses a JSON document, returns the reference to its root element if succeeded.
    bool parse(const std::string_view &, Element &) { throw Exception{"Functions JSON* are not supported", ErrorCodes::NOT_IMPLEMENTED}; }

#if 0
    /// Optional: Allocates memory to parse JSON documents faster.
    void reserve(size_t max_size);
#endif
};

inline ALWAYS_INLINE std::ostream& operator<<(std::ostream& out, DummyJSONParser::Element)
{
    return out;
}

}