//     __ _____ _____ _____
//  __|  |   __|     |   | |  JSON for Modern C++
// |  |  |__   |  |  | | | |  version 3.12.0
// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT

#pragma once

#include <cstddef>
#include <string> // string
#include <type_traits> // enable_if_t
#include <utility> // move
#include <vector> // vector

#include <nlohmann/detail/exceptions.hpp>
#include <nlohmann/detail/input/lexer.hpp>
#include <nlohmann/detail/macro_scope.hpp>
#include <nlohmann/detail/string_concat.hpp>
NLOHMANN_JSON_NAMESPACE_BEGIN

/*!
@brief SAX interface

This class describes the SAX interface used by @ref nlohmann::json::sax_parse.
Each function is called in different situations while the input is parsed. The
boolean return value informs the parser whether to continue processing the
input.
*/
template<typename BasicJsonType>
struct json_sax
{
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    using string_t = typename BasicJsonType::string_t;
    using binary_t = typename BasicJsonType::binary_t;

    /*!
    @brief a null value was read
    @return whether parsing should proceed
    */
    virtual bool null() = 0;

    /*!
    @brief a boolean value was read
    @param[in] val  boolean value
    @return whether parsing should proceed
    */
    virtual bool boolean(bool val) = 0;

    /*!
    @brief an integer number was read
    @param[in] val  integer value
    @return whether parsing should proceed
    */
    virtual bool number_integer(number_integer_t val) = 0;

    /*!
    @brief an unsigned integer number was read
    @param[in] val  unsigned integer value
    @return whether parsing should proceed
    */
    virtual bool number_unsigned(number_unsigned_t val) = 0;

    /*!
    @brief a floating-point number was read
    @param[in] val  floating-point value
    @param[in] s    raw token value
    @return whether parsing should proceed
    */
    virtual bool number_float(number_float_t val, const string_t& s) = 0;

    /*!
    @brief a string value was read
    @param[in] val  string value
    @return whether parsing should proceed
    @note It is safe to move the passed string value.
    */
    virtual bool string(string_t& val) = 0;

    /*!
    @brief a binary value was read
    @param[in] val  binary value
    @return whether parsing should proceed
    @note It is safe to move the passed binary value.
    */
    virtual bool binary(binary_t& val) = 0;

    /*!
    @brief the beginning of an object was read
    @param[in] elements  number of object elements or -1 if unknown
    @return whether parsing should proceed
    @note binary formats may report the number of elements
    */
    virtual bool start_object(std::size_t elements) = 0;

    /*!
    @brief an object key was read
    @param[in] val  object key
    @return whether parsing should proceed
    @note It is safe to move the passed string.
    */
    virtual bool key(string_t& val) = 0;

    /*!
    @brief the end of an object was read
    @return whether parsing should proceed
    */
    virtual bool end_object() = 0;

    /*!
    @brief the beginning of an array was read
    @param[in] elements  number of array elements or -1 if unknown
    @return whether parsing should proceed
    @note binary formats may report the number of elements
    */
    virtual bool start_array(std::size_t elements) = 0;

    /*!
    @brief the end of an array was read
    @return whether parsing should proceed
    */
    virtual bool end_array() = 0;

    /*!
    @brief a parse error occurred
    @param[in] position    the position in the input where the error occurs
    @param[in] last_token  the last read token
    @param[in] ex          an exception object describing the error
    @return whether parsing should proceed (must return false)
    */
    virtual bool parse_error(std::size_t position,
                             const std::string& last_token,
                             const detail::exception& ex) = 0;

    json_sax() = default;
    json_sax(const json_sax&) = default;
    json_sax(json_sax&&) noexcept = default;
    json_sax& operator=(const json_sax&) = default;
    json_sax& operator=(json_sax&&) noexcept = default;
    virtual ~json_sax() = default;
};

namespace detail
{
constexpr std::size_t unknown_size()
{
    return (std::numeric_limits<std::size_t>::max)();
}

/*!
@brief SAX implementation to create a JSON value from SAX events

This class implements the @ref json_sax interface and processes the SAX events
to create a JSON value which makes it basically a DOM parser. The structure or
hierarchy of the JSON value is managed by the stack `ref_stack` which contains
a pointer to the respective array or object for each recursion depth.

After successful parsing, the value that is passed by reference to the
constructor contains the parsed value.

@tparam BasicJsonType  the JSON type
*/
template<typename BasicJsonType, typename InputAdapterType>
class json_sax_dom_parser
{
  public:
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    using string_t = typename BasicJsonType::string_t;
    using binary_t = typename BasicJsonType::binary_t;
    using lexer_t = lexer<BasicJsonType, InputAdapterType>;

    /*!
    @param[in,out] r  reference to a JSON value that is manipulated while
                       parsing
    @param[in] allow_exceptions_  whether parse errors yield exceptions
    */
    explicit json_sax_dom_parser(BasicJsonType& r, const bool allow_exceptions_ = true, lexer_t* lexer_ = nullptr)
        : root(r), allow_exceptions(allow_exceptions_), m_lexer_ref(lexer_)
    {}

    // make class move-only
    json_sax_dom_parser(const json_sax_dom_parser&) = delete;
    json_sax_dom_parser(json_sax_dom_parser&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
    json_sax_dom_parser& operator=(const json_sax_dom_parser&) = delete;
    json_sax_dom_parser& operator=(json_sax_dom_parser&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
    ~json_sax_dom_parser() = default;

    bool null()
    {
        handle_value(nullptr);
        return true;
    }

    bool boolean(bool val)
    {
        handle_value(val);
        return true;
    }

    bool number_integer(number_integer_t val)
    {
        handle_value(val);
        return true;
    }

    bool number_unsigned(number_unsigned_t val)
    {
        handle_value(val);
        return true;
    }

    bool number_float(number_float_t val, const string_t& /*unused*/)
    {
        handle_value(val);
        return true;
    }

    bool string(string_t& val)
    {
        handle_value(val);
        return true;
    }

    bool binary(binary_t& val)
    {
        handle_value(std::move(val));
        return true;
    }

    bool start_object(std::size_t len)
    {
        ref_stack.push_back(handle_value(BasicJsonType::value_t::object));

#if JSON_DIAGNOSTIC_POSITIONS
        // Manually set the start position of the object here.
        // Ensure this is after the call to handle_value to ensure correct start position.
        if (m_lexer_ref)
        {
            // Lexer has read the first character of the object, so
            // subtract 1 from the position to get the correct start position.
            ref_stack.back()->start_position = m_lexer_ref->get_position() - 1;
        }
#endif

        if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref_stack.back()->max_size()))
        {
            JSON_THROW(out_of_range::create(408, concat("excessive object size: ", std::to_string(len)), ref_stack.back()));
        }

        return true;
    }

    bool key(string_t& val)
    {
        JSON_ASSERT(!ref_stack.empty());
        JSON_ASSERT(ref_stack.back()->is_object());

        // add null at the given key and store the reference for later
        object_element = &(ref_stack.back()->m_data.m_value.object->operator[](val));
        return true;
    }

    bool end_object()
    {
        JSON_ASSERT(!ref_stack.empty());
        JSON_ASSERT(ref_stack.back()->is_object());

#if JSON_DIAGNOSTIC_POSITIONS
        if (m_lexer_ref)
        {
            // Lexer's position is past the closing brace, so set that as the end position.
            ref_stack.back()->end_position = m_lexer_ref->get_position();
        }
#endif

        ref_stack.back()->set_parents();
        ref_stack.pop_back();
        return true;
    }

    bool start_array(std::size_t len)
    {
        ref_stack.push_back(handle_value(BasicJsonType::value_t::array));

#if JSON_DIAGNOSTIC_POSITIONS
        // Manually set the start position of the array here.
        // Ensure this is after the call to handle_value to ensure correct start position.
        if (m_lexer_ref)
        {
            ref_stack.back()->start_position = m_lexer_ref->get_position() - 1;
        }
#endif

        if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref_stack.back()->max_size()))
        {
            JSON_THROW(out_of_range::create(408, concat("excessive array size: ", std::to_string(len)), ref_stack.back()));
        }

        return true;
    }

    bool end_array()
    {
        JSON_ASSERT(!ref_stack.empty());
        JSON_ASSERT(ref_stack.back()->is_array());

#if JSON_DIAGNOSTIC_POSITIONS
        if (m_lexer_ref)
        {
            // Lexer's position is past the closing bracket, so set that as the end position.
            ref_stack.back()->end_position = m_lexer_ref->get_position();
        }
#endif

        ref_stack.back()->set_parents();
        ref_stack.pop_back();
        return true;
    }

    template<class Exception>
    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
                     const Exception& ex)
    {
        errored = true;
        static_cast<void>(ex);
        if (allow_exceptions)
        {
            JSON_THROW(ex);
        }
        return false;
    }

    constexpr bool is_errored() const
    {
        return errored;
    }

  private:

#if JSON_DIAGNOSTIC_POSITIONS
    void handle_diagnostic_positions_for_json_value(BasicJsonType& v)
    {
        if (m_lexer_ref)
        {
            // Lexer has read past the current field value, so set the end position to the current position.
            // The start position will be set below based on the length of the string representation
            // of the value.
            v.end_position = m_lexer_ref->get_position();

            switch (v.type())
            {
                case value_t::boolean:
                {
                    // 4 and 5 are the string length of "true" and "false"
                    v.start_position = v.end_position - (v.m_data.m_value.boolean ? 4 : 5);
                    break;
                }

                case value_t::null:
                {
                    // 4 is the string length of "null"
                    v.start_position = v.end_position - 4;
                    break;
                }

                case value_t::string:
                {
                    // escape sequences make the token longer than the value it
                    // parses to, so the start position cannot be derived from
                    // the value; use the offset the lexer recorded instead
                    v.start_position = m_lexer_ref->get_token_start_position();
                    break;
                }

                // As we handle the start and end positions for values created during parsing,
                // we do not expect the following value type to be called. Regardless, set the positions
                // in case this is created manually or through a different constructor. Exclude from lcov
                // since the exact condition of this switch is esoteric.
                // LCOV_EXCL_START
                case value_t::discarded:
                {
                    v.end_position = std::string::npos;
                    v.start_position = v.end_position;
                    break;
                }
                // LCOV_EXCL_STOP
                case value_t::binary:
                case value_t::number_integer:
                case value_t::number_unsigned:
                case value_t::number_float:
                {
                    v.start_position = v.end_position - m_lexer_ref->get_string().size();
                    break;
                }
                case value_t::object:
                case value_t::array:
                {
                    // object and array are handled in start_object() and start_array() handlers
                    // skip setting the values here.
                    break;
                }
                default: // LCOV_EXCL_LINE
                    // Handle all possible types discretely, default handler should never be reached.
                    JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert,-warnings-as-errors) LCOV_EXCL_LINE
            }
        }
    }
#endif

    /*!
    @invariant If the ref stack is empty, then the passed value will be the new
               root.
    @invariant If the ref stack contains a value, then it is an array or an
               object to which we can add elements
    */
    template<typename Value>
    JSON_HEDLEY_RETURNS_NON_NULL
    BasicJsonType* handle_value(Value&& v)
    {
        if (ref_stack.empty())
        {
            root = BasicJsonType(std::forward<Value>(v));

#if JSON_DIAGNOSTIC_POSITIONS
            handle_diagnostic_positions_for_json_value(root);
#endif

            return &root;
        }

        JSON_ASSERT(ref_stack.back()->is_array() || ref_stack.back()->is_object());

        if (ref_stack.back()->is_array())
        {
            ref_stack.back()->m_data.m_value.array->emplace_back(std::forward<Value>(v));

#if JSON_DIAGNOSTIC_POSITIONS
            handle_diagnostic_positions_for_json_value(ref_stack.back()->m_data.m_value.array->back());
#endif

            return &(ref_stack.back()->m_data.m_value.array->back());
        }

        JSON_ASSERT(ref_stack.back()->is_object());
        JSON_ASSERT(object_element);
        *object_element = BasicJsonType(std::forward<Value>(v));

#if JSON_DIAGNOSTIC_POSITIONS
        handle_diagnostic_positions_for_json_value(*object_element);
#endif

        return object_element;
    }

    /// the parsed JSON value
    BasicJsonType& root;
    /// stack to model hierarchy of values
    std::vector<BasicJsonType*> ref_stack {};
    /// helper to hold the reference for the next object element
    BasicJsonType* object_element = nullptr;
    /// whether a syntax error occurred
    bool errored = false;
    /// whether to throw exceptions in case of errors
    const bool allow_exceptions = true;
    /// the lexer reference to obtain the current position
    lexer_t* m_lexer_ref = nullptr;
};

template<typename BasicJsonType, typename InputAdapterType>
class json_sax_dom_callback_parser
{
  public:
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    using string_t = typename BasicJsonType::string_t;
    using binary_t = typename BasicJsonType::binary_t;
    using parser_callback_t = typename BasicJsonType::parser_callback_t;
    using parse_event_t = typename BasicJsonType::parse_event_t;
    using lexer_t = lexer<BasicJsonType, InputAdapterType>;

    json_sax_dom_callback_parser(BasicJsonType& r,
                                 parser_callback_t cb,
                                 const bool allow_exceptions_ = true,
                                 lexer_t* lexer_ = nullptr)
        : root(r), callback(std::move(cb)), allow_exceptions(allow_exceptions_), m_lexer_ref(lexer_)
    {
        keep_stack.push_back(true);
    }

    // make class move-only
    json_sax_dom_callback_parser(const json_sax_dom_callback_parser&) = delete;
    json_sax_dom_callback_parser(json_sax_dom_callback_parser&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
    json_sax_dom_callback_parser& operator=(const json_sax_dom_callback_parser&) = delete;
    json_sax_dom_callback_parser& operator=(json_sax_dom_callback_parser&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
    ~json_sax_dom_callback_parser() = default;

    bool null()
    {
        handle_value(nullptr);
        return true;
    }

    bool boolean(bool val)
    {
        handle_value(val);
        return true;
    }

    bool number_integer(number_integer_t val)
    {
        handle_value(val);
        return true;
    }

    bool number_unsigned(number_unsigned_t val)
    {
        handle_value(val);
        return true;
    }

    bool number_float(number_float_t val, const string_t& /*unused*/)
    {
        handle_value(val);
        return true;
    }

    bool string(string_t& val)
    {
        handle_value(val);
        return true;
    }

    bool binary(binary_t& val)
    {
        handle_value(std::move(val));
        return true;
    }

    bool start_object(std::size_t len)
    {
        // check callback for object start
        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::object_start, discarded);
        keep_stack.push_back(keep);

        // the key this object will be stored under, read before handle_value()
        // may consume it; kept in lockstep with ref_stack so end_object() can
        // find the object in its parent again
        container_key_stack.push_back(current_key());

        auto val = handle_value(BasicJsonType::value_t::object, true);
        ref_stack.push_back(val.second);

        if (ref_stack.back())
        {

#if JSON_DIAGNOSTIC_POSITIONS
            // Manually set the start position of the object here.
            // Ensure this is after the call to handle_value to ensure correct start position.
            if (m_lexer_ref)
            {
                // Lexer has read the first character of the object, so
                // subtract 1 from the position to get the correct start position.
                ref_stack.back()->start_position = m_lexer_ref->get_position() - 1;
            }
#endif

            // check object limit
            if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref_stack.back()->max_size()))
            {
                JSON_THROW(out_of_range::create(408, concat("excessive object size: ", std::to_string(len)), ref_stack.back()));
            }
        }
        return true;
    }

    bool key(string_t& val)
    {
        BasicJsonType k = BasicJsonType(val);

        // check callback for the key
        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::key, k);
        key_keep_stack.push_back(keep);
        // remember the key so a rejected value can be erased without searching
        // the object for it (kept in lockstep with key_keep_stack)
        key_stack.push_back(val);

        // add discarded value at the given key and store the reference for later
        if (keep && ref_stack.back())
        {
            object_element = &(ref_stack.back()->m_data.m_value.object->operator[](val) = discarded);
        }

        return true;
    }

    bool end_object()
    {
        if (ref_stack.back())
        {
            if (!callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::object_end, *ref_stack.back()))
            {
                // discard object
                *ref_stack.back() = discarded;

#if JSON_DIAGNOSTIC_POSITIONS
                // Set start/end positions for discarded object.
                handle_diagnostic_positions_for_json_value(*ref_stack.back());
#endif
            }
            else
            {

#if JSON_DIAGNOSTIC_POSITIONS
                if (m_lexer_ref)
                {
                    // Lexer's position is past the closing brace, so set that as the end position.
                    ref_stack.back()->end_position = m_lexer_ref->get_position();
                }
#endif

                ref_stack.back()->set_parents();
            }
        }

        JSON_ASSERT(!ref_stack.empty());
        JSON_ASSERT(!keep_stack.empty());
        JSON_ASSERT(!container_key_stack.empty());
        ref_stack.pop_back();
        keep_stack.pop_back();
        const string_t object_key = std::move(container_key_stack.back());
        container_key_stack.pop_back();

        if (!ref_stack.empty() && ref_stack.back() && ref_stack.back()->is_structured())
        {
            // remove discarded value
            remove_discarded_value(*ref_stack.back(), object_key);
        }

        return true;
    }

    bool start_array(std::size_t len)
    {
        const bool keep = callback(static_cast<int>(ref_stack.size()), parse_event_t::array_start, discarded);
        keep_stack.push_back(keep);

        // see start_object()
        container_key_stack.push_back(current_key());

        auto val = handle_value(BasicJsonType::value_t::array, true);
        ref_stack.push_back(val.second);

        if (ref_stack.back())
        {

#if JSON_DIAGNOSTIC_POSITIONS
            // Manually set the start position of the array here.
            // Ensure this is after the call to handle_value to ensure correct start position.
            if (m_lexer_ref)
            {
                // Lexer has read the first character of the array, so
                // subtract 1 from the position to get the correct start position.
                ref_stack.back()->start_position = m_lexer_ref->get_position() - 1;
            }
#endif

            // check array limit
            if (JSON_HEDLEY_UNLIKELY(len != detail::unknown_size() && len > ref_stack.back()->max_size()))
            {
                JSON_THROW(out_of_range::create(408, concat("excessive array size: ", std::to_string(len)), ref_stack.back()));
            }
        }

        return true;
    }

    bool end_array()
    {
        bool keep = true;
        const bool stored = ref_stack.back() != nullptr;

        if (stored)
        {
            keep = callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::array_end, *ref_stack.back());
            if (keep)
            {

#if JSON_DIAGNOSTIC_POSITIONS
                if (m_lexer_ref)
                {
                    // Lexer's position is past the closing bracket, so set that as the end position.
                    ref_stack.back()->end_position = m_lexer_ref->get_position();
                }
#endif

                ref_stack.back()->set_parents();
            }
            else
            {
                // discard array
                *ref_stack.back() = discarded;

#if JSON_DIAGNOSTIC_POSITIONS
                // Set start/end positions for discarded array.
                handle_diagnostic_positions_for_json_value(*ref_stack.back());
#endif
            }
        }

        JSON_ASSERT(!ref_stack.empty());
        JSON_ASSERT(!keep_stack.empty());
        JSON_ASSERT(!container_key_stack.empty());
        ref_stack.pop_back();
        keep_stack.pop_back();
        const string_t object_key = std::move(container_key_stack.back());
        container_key_stack.pop_back();

        // remove discarded value
        if (!ref_stack.empty() && ref_stack.back())
        {
            if (!keep && ref_stack.back()->is_array())
            {
                ref_stack.back()->m_data.m_value.array->pop_back();
            }
            else if ((!keep || !stored) && ref_stack.back()->is_object())
            {
                // the array is either still stored under its key or was never
                // stored, leaving the placeholder key() wrote; both show up as
                // a discarded member of the parent object
                remove_discarded_value(*ref_stack.back(), object_key);
            }
        }

        return true;
    }

    template<class Exception>
    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/,
                     const Exception& ex)
    {
        errored = true;
        static_cast<void>(ex);
        if (allow_exceptions)
        {
            JSON_THROW(ex);
        }
        return false;
    }

    constexpr bool is_errored() const
    {
        return errored;
    }

  private:

#if JSON_DIAGNOSTIC_POSITIONS
    void handle_diagnostic_positions_for_json_value(BasicJsonType& v)
    {
        if (m_lexer_ref)
        {
            // Lexer has read past the current field value, so set the end position to the current position.
            // The start position will be set below based on the length of the string representation
            // of the value.
            v.end_position = m_lexer_ref->get_position();

            switch (v.type())
            {
                case value_t::boolean:
                {
                    // 4 and 5 are the string length of "true" and "false"
                    v.start_position = v.end_position - (v.m_data.m_value.boolean ? 4 : 5);
                    break;
                }

                case value_t::null:
                {
                    // 4 is the string length of "null"
                    v.start_position = v.end_position - 4;
                    break;
                }

                case value_t::string:
                {
                    // escape sequences make the token longer than the value it
                    // parses to, so the start position cannot be derived from
                    // the value; use the offset the lexer recorded instead
                    v.start_position = m_lexer_ref->get_token_start_position();
                    break;
                }

                case value_t::discarded:
                {
                    v.end_position = std::string::npos;
                    v.start_position = v.end_position;
                    break;
                }

                case value_t::binary:
                case value_t::number_integer:
                case value_t::number_unsigned:
                case value_t::number_float:
                {
                    v.start_position = v.end_position - m_lexer_ref->get_string().size();
                    break;
                }

                case value_t::object:
                case value_t::array:
                {
                    // object and array are handled in start_object() and start_array() handlers
                    // skip setting the values here.
                    break;
                }
                default: // LCOV_EXCL_LINE
                    // Handle all possible types discretely, default handler should never be reached.
                    JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert,-warnings-as-errors) LCOV_EXCL_LINE
            }
        }
    }
#endif

    /*!
    @brief the key the value now being handled will be stored under

    Empty unless the enclosing container is an object, in which case it is the
    key of the pending key() event. Read before handle_value() consumes that
    key, so it is also correct when the value never reaches its parent.
    */
    string_t current_key() const
    {
        if (!ref_stack.empty() && ref_stack.back() && ref_stack.back()->is_object()
                && !key_stack.empty())
        {
            return key_stack.back();
        }
        return string_t{};
    }

    /*!
    @brief remove the discarded value the callback rejected from its parent

    A rejected value can only ever be the one most recently added to @a parent:
    the last element of an array, or the placeholder key() stored under @a key
    in an object. Looking there directly makes this O(1) resp. O(log n), where
    searching @a parent for it made a filtering parse quadratic in the number of
    members of a single container.

    Finding no discarded value there means none was stored in the first place -
    the callback rejected the value before it reached its parent - so there is
    nothing to remove.

    @param[in,out] parent  the container to remove the rejected value from
    @param[in] key  the key the value was stored under; unused for arrays
    */
    static void remove_discarded_value(BasicJsonType& parent, const string_t& key)
    {
        if (parent.is_array())
        {
            auto& array = *parent.m_data.m_value.array;
            if (!array.empty() && array.back().is_discarded())
            {
                array.pop_back();
            }
        }
        else if (parent.is_object())
        {
            auto& object = *parent.m_data.m_value.object;
            const auto it = object.find(key);
            if (it != object.end() && it->second.is_discarded())
            {
                object.erase(it);
            }
        }
    }

    /*!
    @param[in] v  value to add to the JSON value we build during parsing
    @param[in] skip_callback  whether we should skip calling the callback
               function; this is required after start_array() and
               start_object() SAX events, because otherwise we would call the
               callback function with an empty array or object, respectively.

    @invariant If the ref stack is empty, then the passed value will be the new
               root.
    @invariant If the ref stack contains a value, then it is an array or an
               object to which we can add elements

    @return pair of boolean (whether value should be kept) and pointer (to the
            passed value in the ref_stack hierarchy; nullptr if not kept)
    */
    template<typename Value>
    std::pair<bool, BasicJsonType*> handle_value(Value&& v, const bool skip_callback = false)
    {
        JSON_ASSERT(!keep_stack.empty());

        // do not handle this value if we know it would be added to a discarded
        // container
        if (!keep_stack.back())
        {
            return {false, nullptr};
        }

        // create value
        auto value = BasicJsonType(std::forward<Value>(v));

#if JSON_DIAGNOSTIC_POSITIONS
        handle_diagnostic_positions_for_json_value(value);
#endif

        // check callback
        const bool keep = skip_callback || callback(static_cast<int>(ref_stack.size()), parse_event_t::value, value);

        // do not handle this value if we just learnt it shall be discarded
        if (!keep)
        {
            // if the value was to become an object member, key() already
            // stored a placeholder for it that has to be removed again
            if (!ref_stack.empty() && ref_stack.back() && ref_stack.back()->is_object())
            {
                JSON_ASSERT(!key_keep_stack.empty());
                JSON_ASSERT(!key_stack.empty());
                const bool placeholder_stored = key_keep_stack.back();
                key_keep_stack.pop_back();
                const string_t key = std::move(key_stack.back());
                key_stack.pop_back();
                if (placeholder_stored)
                {
                    remove_discarded_value(*ref_stack.back(), key);
                }
            }
            return {false, nullptr};
        }

        if (ref_stack.empty())
        {
            root = std::move(value);
            return {true, & root};
        }

        // skip this value if we already decided to skip the parent
        // (https://github.com/nlohmann/json/issues/971#issuecomment-413678360)
        if (!ref_stack.back())
        {
            return {false, nullptr};
        }

        // we now only expect arrays and objects
        JSON_ASSERT(ref_stack.back()->is_array() || ref_stack.back()->is_object());

        // array
        if (ref_stack.back()->is_array())
        {
            ref_stack.back()->m_data.m_value.array->emplace_back(std::move(value));
            return {true, & (ref_stack.back()->m_data.m_value.array->back())};
        }

        // object
        JSON_ASSERT(ref_stack.back()->is_object());
        // check if we should store an element for the current key
        JSON_ASSERT(!key_keep_stack.empty());
        JSON_ASSERT(!key_stack.empty());
        const bool store_element = key_keep_stack.back();
        key_keep_stack.pop_back();
        key_stack.pop_back();

        if (!store_element)
        {
            return {false, nullptr};
        }

        JSON_ASSERT(object_element);
        *object_element = std::move(value);
        return {true, object_element};
    }

    /// the parsed JSON value
    BasicJsonType& root;
    /// stack to model hierarchy of values
    std::vector<BasicJsonType*> ref_stack {};
    /// stack to manage which values to keep
    std::vector<bool> keep_stack {}; // NOLINT(readability-redundant-member-init)
    /// stack to manage which object keys to keep
    std::vector<bool> key_keep_stack {}; // NOLINT(readability-redundant-member-init)
    /// the keys key() stored a placeholder for, in lockstep with key_keep_stack
    std::vector<string_t> key_stack {}; // NOLINT(readability-redundant-member-init)
    /// for each open container, the key it is stored under in its parent
    /// object, in lockstep with ref_stack; unused where the parent is not an
    /// object
    std::vector<string_t> container_key_stack {}; // NOLINT(readability-redundant-member-init)
    /// helper to hold the reference for the next object element
    BasicJsonType* object_element = nullptr;
    /// whether a syntax error occurred
    bool errored = false;
    /// callback function
    const parser_callback_t callback = nullptr;
    /// whether to throw exceptions in case of errors
    const bool allow_exceptions = true;
    /// a discarded value for the callback
    BasicJsonType discarded = BasicJsonType::value_t::discarded;
    /// the lexer reference to obtain the current position
    lexer_t* m_lexer_ref = nullptr;
};

template<typename BasicJsonType>
class json_sax_acceptor
{
  public:
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    using string_t = typename BasicJsonType::string_t;
    using binary_t = typename BasicJsonType::binary_t;

    bool null()
    {
        return true;
    }

    bool boolean(bool /*unused*/)
    {
        return true;
    }

    bool number_integer(number_integer_t /*unused*/)
    {
        return true;
    }

    bool number_unsigned(number_unsigned_t /*unused*/)
    {
        return true;
    }

    bool number_float(number_float_t /*unused*/, const string_t& /*unused*/)
    {
        return true;
    }

    bool string(string_t& /*unused*/)
    {
        return true;
    }

    bool binary(binary_t& /*unused*/)
    {
        return true;
    }

    bool start_object(std::size_t /*unused*/ = detail::unknown_size())
    {
        return true;
    }

    bool key(string_t& /*unused*/)
    {
        return true;
    }

    bool end_object()
    {
        return true;
    }

    bool start_array(std::size_t /*unused*/ = detail::unknown_size())
    {
        return true;
    }

    bool end_array()
    {
        return true;
    }

    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const detail::exception& /*unused*/)
    {
        return false;
    }
};

}  // namespace detail
NLOHMANN_JSON_NAMESPACE_END