tting ) {
			case 'post_types_blacklist':
				$default_array_value = Defaults::$blacklisted_post_types;
				break;
			case 'taxonomies_blacklist':
				$default_array_value = Defaults::$blacklisted_taxonomies;
				break;
			case 'post_meta_whitelist':
				$default_array_value = Defaults::get_post_meta_whitelist();
				break;
			case 'comment_meta_whitelist':
				$default_array_value = Defaults::get_comment_meta_whitelist();
				break;
			case 'known_importers':
				$default_array_value = Defaults::get_known_importers();
				break;
		}

		if ( $default_array_value ) {
			if ( is_array( $value ) ) {
				$value = array_unique( array_merge( $value, $default_array_value ) );
			} else {
				$value = $default_array_value;
			}
		}

		return $value;
	}

	/**
	 * Change multiple settings in the same time.
	 *
	 * @access public
	 * @static
	 *
	 * @param array $new_settings The new settings.
	 */
	public static function update_settings( $new_settings ) {
		$validated_settings = array_intersect_key( $new_settings, self::$valid_settings );
		foreach ( $validated_settings as $setting => $value ) {

			if ( self::is_network_setting( $setting ) ) {
				if ( is_multisite() && is_main_site() ) {
					update_site_option( self::SETTINGS_OPTION_PREFIX . $setting, $value );
				}
			} else {
				update_option( self::SETTINGS_OPTION_PREFIX . $setting, $value, true );
			}

			// If we set the disabled option to true, clear the queues.
			if ( ( 'disable' === $setting || 'network_disable' === $setting ) && (bool) $value ) {
				$listener = Listener::get_instance();
				$listener->get_sync_queue()->reset();
				$listener->get_full_sync_queue()->reset();
			}
		}
	}

	/**
	 * Whether the specified setting is a network setting.
	 *
	 * @access public
	 * @static
	 *
	 * @param string $setting Setting name.
	 * @return boolean Whether the setting is a network setting.
	 */
	public static function is_network_setting( $setting ) {
		return strpos( $setting, 'network_' ) === 0;
	}

	/**
	 * Returns escaped SQL for blacklisted post types.
	 * Can be injected directly into a WHERE clause.
	 *
	 * @access public
	 * @static
	 *
	 * @return string SQL WHERE clause.
	 */
	public static function get_blacklisted_post_types_sql() {
		return 'post_type NOT IN (\'' . join( '\', \'', array_map( 'esc_sql', self::get_setting( 'post_types_blacklist' ) ) ) . '\')';
	}

	/**
	 * Returns escaped values for disallowed post types.
	 *
	 * @access public
	 * @static
	 *
	 * @return array Post type filter values
	 */
	public static function get_disallowed_post_types_structured() {
		return array(
			'post_type' => array(
				'operator' => 'NOT IN',
				'values'   => array_map( 'esc_sql', self::get_setting( 'post_types_blacklist' ) ),
			),
		);
	}

	/**
	 * Returns escaped SQL for blacklisted taxonomies.
	 * Can be injected directly into a WHERE clause.
	 *
	 * @access public
	 * @static
	 *
	 * @return string SQL WHERE clause.
	 */
	public static function get_blacklisted_taxonomies_sql() {
		return "taxonomy NOT IN ('" . join( "', '", array_map( 'esc_sql', self::get_setting( 'taxonomies_blacklist' ) ) ) . "')";
	}

	/**
	 * Returns escaped SQL for blacklisted post meta.
	 * Can be injected directly into a WHERE clause.
	 *
	 * @access public
	 * @static
	 *
	 * @return string SQL WHERE clause.
	 */
	public static function get_whitelisted_post_meta_sql() {
		return 'meta_key IN (\'' . join( '\', \'', array_map( 'esc_sql', self::get_setting( 'post_meta_whitelist' ) ) ) . '\')';
	}

	/**
	 * Returns escaped SQL for allowed post meta keys.
	 *
	 * @access public
	 * @static
	 *
	 * @return array Meta keys filter values
	 */
	public static function get_allowed_post_meta_structured() {
		return array(
			'meta_key' => array(
				'operator' => 'IN',
				'values'   => array_map( 'esc_sql', self::get_setting( 'post_meta_whitelist' ) ),
			),
		);
	}

	/**
	 * Returns structured SQL clause for blacklisted taxonomies.
	 *
	 * @access public
	 * @static
	 *
	 * @return array taxonomies filter values
	 */
	public static function get_blacklisted_taxonomies_structured() {
		return array(
			'taxonomy' => array(
				'operator' => 'NOT IN',
				'values'   => array_map( 'esc_sql', self::get_setting( 'taxonomies_blacklist' ) ),
			),
		);
	}

	/**
	 * Returns escaped SQL for blacklisted comment meta.
	 * Can be injected directly into a WHERE clause.
	 *
	 * @access public
	 * @static
	 *
	 * @return string SQL WHERE clause.
	 */
	public static function get_whitelisted_comment_meta_sql() {
		return 'meta_key IN (\'' . join( '\', \'', array_map( 'esc_sql', self::get_setting( 'comment_meta_whitelist' ) ) ) . '\')';
	}

	/**
	 * Returns SQL-escaped values for allowed post meta keys.
	 *
	 * @access public
	 * @static
	 *
	 * @return array Meta keys filter values
	 */
	public static function get_allowed_comment_meta_structured() {
		return array(
			'meta_key' => array(
				'operator' => 'IN',
				'values'   => array_map( 'esc_sql', self::get_setting( 'comment_meta_whitelist' ) ),
			),
		);
	}

	/**
	 * Returns escaped SQL for comments, excluding any spam comments.
	 * Can be injected directly into a WHERE clause.
	 *
	 * @access public
	 * @static
	 *
	 * @return string SQL WHERE clause.
	 */
	public static function get_comments_filter_sql() {
		return "comment_approved <> 'spam'";
	}

	/**
	 * Delete any settings options and clean up the current settings state.
	 *
	 * @access public
	 * @static
	 */
	public static function reset_data() {
		$valid_settings = self::$valid_settings;
		foreach ( $valid_settings as $option => $value ) {
			delete_option( self::SETTINGS_OPTION_PREFIX . $option );
		}
		self::set_importing( null );
		self::set_doing_cron( null );
		self::set_is_syncing( null );
		self::set_is_sending( null );
	}

	/**
	 * Set the importing state.
	 *
	 * @access public
	 * @static
	 *
	 * @param boolean $is_importing Whether WordPress is currently importing.
	 */
	public static function set_importing( $is_importing ) {
		// Set to NULL to revert to WP_IMPORTING, the standard behavior.
		self::$is_importing = $is_importing;
	}

	/**
	 * Whether WordPress is currently importing.
	 *
	 * @access public
	 * @static
	 *
	 * @return boolean Whether WordPress is currently importing.
	 */
	public static function is_importing() {
		if ( ! is_null( self::$is_importing ) ) {
			return self::$is_importing;
		}

		return defined( 'WP_IMPORTING' ) && WP_IMPORTING;
	}

	/**
	 * Whether sync is enabled.
	 *
	 * @access public
	 * @static
	 *
	 * @return boolean Whether sync is enabled.
	 */
	public static function is_sync_enabled() {
		return ! ( self::get_setting( 'disable' ) || self::get_setting( 'network_disable' ) );
	}

	/**
	 * Set the WP cron state.
	 *
	 * @access public
	 * @static
	 *
	 * @param boolean $is_doing_cron Whether WordPress is currently doing WP cron.
	 */
	public static function set_doing_cron( $is_doing_cron ) {
		// Set to NULL to revert to WP_IMPORTING, the standard behavior.
		self::$is_doing_cron = $is_doing_cron;
	}

	/**
	 * Whether WordPress is currently doing WP cron.
	 *
	 * @access public
	 * @static
	 *
	 * @return boolean Whether WordPress is currently doing WP cron.
	 */
	public static function is_doing_cron() {
		if ( ! is_null( self::$is_doing_cron ) ) {
			return self::$is_doing_cron;
		}

		return defined( 'DOING_CRON' ) && DOING_CRON;
	}

	/**
	 * Whether we are currently syncing.
	 *
	 * @access public
	 * @static
	 *
	 * @return boolean Whether we are currently syncing.
	 */
	public static function is_syncing() {
		return (bool) self::$is_syncing || ( defined( 'REST_API_REQUEST' ) && REST_API_REQUEST );
	}

	/**
	 * Set the syncing state.
	 *
	 * @access public
	 * @static
	 *
	 * @param boolean $is_syncing Whether we are currently syncing.
	 */
	public static function set_is_syncing( $is_syncing ) {
		self::$is_syncing = $is_syncing;
	}

	/**
	 * Whether we are currently sending sync items.
	 *
	 * @access public
	 * @static
	 *
	 * @return boolean Whether we are currently sending sync items.
	 */
	public static function is_sending() {
		return (bool) self::$is_sending;
	}

	/**
	 * Set the sending state.
	 *
	 * @access public
	 * @static
	 *
	 * @param boolean $is_sending Whether we are currently sending sync items.
	 */
	public static function set_is_sending( $is_sending ) {
		self::$is_sending = $is_sending;
	}

	/**
	 * Whether should send from the queue
	 *
	 * @access public
	 * @static
	 *
	 * @param string $queue_id The queue identifier.
	 *
	 * @return boolean Whether sync is enabled.
	 */
	public static function is_sender_enabled( $queue_id ) {
		return (bool) self::get_setting( $queue_id . '_sender_enabled' );
	}

	/**
	 * Whether checksums are enabled.
	 *
	 * @access public
	 * @static
	 *
	 * @return boolean Whether sync is enabled.
	 */
	public static function is_checksum_enabled() {
		return ! (bool) self::get_setting( 'checksum_disable' );
	}

}