@param string $subtype      The object subtype.
	 * @param mixed  $stored_value The currently stored value retrieved from get_metadata().
	 * @param mixed  $user_value   The value provided by the user.
	 * @return bool
	 */
	protected function is_meta_value_same_as_stored_value( $meta_key, $subtype, $stored_value, $user_value ) {
		$args      = $this->get_registered_fields()[ $meta_key ];
		$sanitized = sanitize_meta( $meta_key, $user_value, $this->get_meta_type(), $subtype );

		if ( in_array( $args['type'], array( 'string', 'number', 'integer', 'boolean' ), true ) ) {
			// The return value of get_metadata will always be a string for scalar types.
			$sanitized = (string) $sanitized;
		}

		return $sanitized === $stored_value;
	}

	/**
	 * Retrieves all the registered meta fields.
	 *
	 * @since 4.7.0
	 *
	 * @return array Registered fields.
	 */
	protected function get_registered_fields() {
		$registered = array();

		$meta_type    = $this->get_meta_type();
		$meta_subtype = $this->get_meta_subtype();

		$meta_keys = get_registered_meta_keys( $meta_type );
		if ( ! empty( $meta_subtype ) ) {
			$meta_keys = array_merge( $meta_keys, get_registered_meta_keys( $meta_type, $meta_subtype ) );
		}

		foreach ( $meta_keys as $name => $args ) {
			if ( empty( $args['show_in_rest'] ) ) {
				continue;
			}

			$rest_args = array();

			if ( is_array( $args['show_in_rest'] ) ) {
				$rest_args = $args['show_in_rest'];
			}

			$default_args = array(
				'name'             => $name,
				'single'           => $args['single'],
				'type'             => ! empty( $args['type'] ) ? $args['type'] : null,
				'schema'           => array(),
				'prepare_callback' => array( $this, 'prepare_value' ),
			);

			$default_schema = array(
				'type'        => $default_args['type'],
				'title'       => empty( $args['label'] ) ? '' : $args['label'],
				'description' => empty( $args['description'] ) ? '' : $args['description'],
				'default'     => isset( $args['default'] ) ? $args['default'] : null,
			);

			$rest_args           = array_merge( $default_args, $rest_args );
			$rest_args['schema'] = array_merge( $default_schema, $rest_args['schema'] );

			$type = ! empty( $rest_args['type'] ) ? $rest_args['type'] : null;
			$type = ! empty( $rest_args['schema']['type'] ) ? $rest_args['schema']['type'] : $type;

			if ( null === $rest_args['schema']['default'] ) {
				$rest_args['schema']['default'] = static::get_empty_value_for_type( $type );
			}

			$rest_args['schema'] = rest_default_additional_properties_to_false( $rest_args['schema'] );

			if ( ! in_array( $type, array( 'string', 'boolean', 'integer', 'number', 'array', 'object' ), true ) ) {
				continue;
			}

			if ( empty( $rest_args['single'] ) ) {
				$rest_args['schema'] = array(
					'type'  => 'array',
					'items' => $rest_args['schema'],
				);
			}

			$registered[ $name ] = $rest_args;
		}

		return $registered;
	}

	/**
	 * Retrieves the object's meta schema, conforming to JSON Schema.
	 *
	 * @since 4.7.0
	 *
	 * @return array Field schema data.
	 */
	public function get_field_schema() {
		$fields = $this->get_registered_fields();

		$schema = array(
			'description' => __( 'Meta fields.' ),
			'type'        => 'object',
			'context'     => array( 'view', 'edit' ),
			'properties'  => array(),
			'arg_options' => array(
				'sanitize_callback' => null,
				'validate_callback' => array( $this, 'check_meta_is_array' ),
			),
		);

		foreach ( $fields as $args ) {
			$schema['properties'][ $args['name'] ] = $args['schema'];
		}

		return $schema;
	}

	/**
	 * Prepares a meta value for output.
	 *
	 * Default preparation for meta fields. Override by passing the
	 * `prepare_callback` in your `show_in_rest` options.
	 *
	 * @since 4.7.0
	 *
	 * @param mixed           $value   Meta value from the database.
	 * @param WP_REST_Request $request Request object.
	 * @param array           $args    REST-specific options for the meta key.
	 * @return mixed Value prepared for output. If a non-JsonSerializable object, null.
	 */
	public static function prepare_value( $value, $request, $args ) {
		if ( $args['single'] ) {
			$schema = $args['schema'];
		} else {
			$schema = $args['schema']['items'];
		}

		if ( '' === $value && in_array( $schema['type'], array( 'boolean', 'integer', 'number' ), true ) ) {
			$value = static::get_empty_value_for_type( $schema['type'] );
		}

		if ( is_wp_error( rest_validate_value_from_schema( $value, $schema ) ) ) {
			return null;
		}

		return rest_sanitize_value_from_schema( $value, $schema );
	}

	/**
	 * Check the 'meta' value of a request is an associative array.
	 *
	 * @since 4.7.0
	 *
	 * @param mixed           $value   The meta value submitted in the request.
	 * @param WP_REST_Request $request Full details about the request.
	 * @param string          $param   The parameter name.
	 * @return array|false The meta array, if valid, false otherwise.
	 */
	public function check_meta_is_array( $value, $request, $param ) {
		if ( ! is_array( $value ) ) {
			return false;
		}

		return $value;
	}

	/**
	 * Recursively add additionalProperties = false to all objects in a schema if no additionalProperties setting
	 * is specified.
	 *
	 * This is needed to restrict properties of objects in meta values to only
	 * registered items, as the REST API will allow additional properties by
	 * default.
	 *
	 * @since 5.3.0
	 * @deprecated 5.6.0 Use rest_default_additional_properties_to_false() instead.
	 *
	 * @param array $schema The schema array.
	 * @return array
	 */
	protected function default_additional_properties_to_false( $schema ) {
		_deprecated_function( __METHOD__, '5.6.0', 'rest_default_additional_properties_to_false()' );

		return rest_default_additional_properties_to_false( $schema );
	}

	/**
	 * Gets the empty value for a schema type.
	 *
	 * @since 5.3.0
	 *
	 * @param string $type The schema type.
	 * @return mixed
	 */
	protected static function get_empty_value_for_type( $type ) {
		switch ( $type ) {
			case 'string':
				return '';
			case 'boolean':
				return false;
			case 'integer':
				return 0;
			case 'number':
				return 0.0;
			case 'array':
			case 'object':
				return array();
			default:
				return null;
		}
	}
}