to existing modules for sending.
	 *
	 * @access public
	 * @static
	 *
	 * @param array $sync_modules The list of sync modules declared prior to this filer.
	 * @return array A list of sync modules that now includes WP Super Cache's modules.
	 */
	public static function add_wp_super_cache_sync_module( $sync_modules ) {
		$sync_modules[] = 'Automattic\\Jetpack\\Sync\\Modules\\WP_Super_Cache';
		return $sync_modules;
	}

	/**
	 * Sanitizes the name of sync's cron schedule.
	 *
	 * @access public
	 * @static
	 *
	 * @param string $schedule The name of a WordPress cron schedule.
	 * @return string The sanitized name of sync's cron schedule.
	 */
	public static function sanitize_filtered_sync_cron_schedule( $schedule ) {
		$schedule  = sanitize_key( $schedule );
		$schedules = wp_get_schedules();

		// Make sure that the schedule has actually been registered using the `cron_intervals` filter.
		if ( isset( $schedules[ $schedule ] ) ) {
			return $schedule;
		}

		return self::DEFAULT_SYNC_CRON_INTERVAL_NAME;
	}

	/**
	 * Allows offsetting of start times for sync cron jobs.
	 *
	 * @access public
	 * @static
	 *
	 * @param string $schedule The name of a cron schedule.
	 * @param string $hook     The hook that this method is responding to.
	 * @return int The offset for the sync cron schedule.
	 */
	public static function get_start_time_offset( $schedule = '', $hook = '' ) {
		$start_time_offset = is_multisite()
			? wp_rand( 0, ( 2 * self::DEFAULT_SYNC_CRON_INTERVAL_VALUE ) )
			: 0;

		/**
		 * Allows overriding the offset that the sync cron jobs will first run. This can be useful when scheduling
		 * cron jobs across multiple sites in a network.
		 *
		 * @since 1.6.3
		 * @since-jetpack 4.5.0
		 *
		 * @param int    $start_time_offset
		 * @param string $hook
		 * @param string $schedule
		 */
		return (int) apply_filters(
			'jetpack_sync_cron_start_time_offset',
			$start_time_offset,
			$hook,
			$schedule
		);
	}

	/**
	 * Decides if a sync cron should be scheduled.
	 *
	 * @access public
	 * @static
	 *
	 * @param string $schedule The name of a cron schedule.
	 * @param string $hook     The hook that this method is responding to.
	 */
	public static function maybe_schedule_sync_cron( $schedule, $hook ) {
		if ( ! $hook ) {
			return;
		}
		$schedule = self::sanitize_filtered_sync_cron_schedule( $schedule );

		$start_time = time() + self::get_start_time_offset( $schedule, $hook );
		if ( ! wp_next_scheduled( $hook ) ) {
			// Schedule a job to send pending queue items once a minute.
			wp_schedule_event( $start_time, $schedule, $hook );
		} elseif ( wp_get_schedule( $hook ) !== $schedule ) {
			// If the schedule has changed, update the schedule.
			wp_clear_scheduled_hook( $hook );
			wp_schedule_event( $start_time, $schedule, $hook );
		}
	}

	/**
	 * Clears Jetpack sync cron jobs.
	 *
	 * @access public
	 * @static
	 */
	public static function clear_sync_cron_jobs() {
		wp_clear_scheduled_hook( 'jetpack_sync_cron' );
		wp_clear_scheduled_hook( 'jetpack_sync_full_cron' );
	}

	/**
	 * Initializes Jetpack sync cron jobs.
	 *
	 * @access public
	 * @static
	 */
	public static function init_sync_cron_jobs() {
		add_filter( 'cron_schedules', array( __CLASS__, 'jetpack_cron_schedule' ) ); // phpcs:ignore WordPress.WP.CronInterval.ChangeDetected

		add_action( 'jetpack_sync_cron', array( __CLASS__, 'do_cron_sync' ) );
		add_action( 'jetpack_sync_full_cron', array( __CLASS__, 'do_cron_full_sync' ) );

		/**
		 * Allows overriding of the default incremental sync cron schedule which defaults to once every 5 minutes.
		 *
		 * @since 1.6.3
		 * @since-jetpack 4.3.2
		 *
		 * @param string self::DEFAULT_SYNC_CRON_INTERVAL_NAME
		 */
		$incremental_sync_cron_schedule = apply_filters( 'jetpack_sync_incremental_sync_interval', self::DEFAULT_SYNC_CRON_INTERVAL_NAME );
		self::maybe_schedule_sync_cron( $incremental_sync_cron_schedule, 'jetpack_sync_cron' );

		/**
		 * Allows overriding of the full sync cron schedule which defaults to once every 5 minutes.
		 *
		 * @since 1.6.3
		 * @since-jetpack 4.3.2
		 *
		 * @param string self::DEFAULT_SYNC_CRON_INTERVAL_NAME
		 */
		$full_sync_cron_schedule = apply_filters( 'jetpack_sync_full_sync_interval', self::DEFAULT_SYNC_CRON_INTERVAL_NAME );
		self::maybe_schedule_sync_cron( $full_sync_cron_schedule, 'jetpack_sync_full_cron' );
	}

	/**
	 * Perform maintenance when a plugin upgrade occurs.
	 *
	 * @access public
	 * @static
	 *
	 * @param string $new_version New version of the plugin.
	 * @param string $old_version Old version of the plugin.
	 */
	public static function cleanup_on_upgrade( $new_version = '', $old_version = '' ) {
		if ( wp_next_scheduled( 'jetpack_sync_send_db_checksum' ) ) {
			wp_clear_scheduled_hook( 'jetpack_sync_send_db_checksum' );
		}

		$is_new_sync_upgrade = version_compare( $old_version, '4.2', '>=' );
		if ( ! empty( $old_version ) && $is_new_sync_upgrade && version_compare( $old_version, '4.5', '<' ) ) {
			self::clear_sync_cron_jobs();
			Settings::update_settings(
				array(
					'render_filtered_content' => Defaults::$default_render_filtered_content,
				)
			);
		}

		Health::on_jetpack_upgraded();
	}

	/**
	 * Get syncing status for the given fields.
	 *
	 * @access public
	 * @static
	 *
	 * @param string|null $fields A comma-separated string of the fields to include in the array from the JSON response.
	 * @return array An associative array with the status report.
	 */
	public static function get_sync_status( $fields = null ) {
		self::initialize_sender();

		$sync_module = Modules::get_module( 'full-sync' );
		$queue       = self::$sender->get_sync_queue();

		// _get_cron_array can be false
		$cron_timestamps = ( _get_cron_array() ) ? array_keys( _get_cron_array() ) : array();
		$next_cron       = ( ! empty( $cron_timestamps ) ) ? $cron_timestamps[0] - time() : '';

		$checksums = array();
		$debug     = array();

		if ( ! empty( $fields ) ) {
			$store         = new Replicastore();
			$fields_params = array_map( 'trim', explode( ',', $fields ) );

			if ( in_array( 'posts_checksum', $fields_params, true ) ) {
				$checksums['posts_checksum'] = $store->posts_checksum();
			}
			if ( in_array( 'comments_checksum', $fields_params, true ) ) {
				$checksums['comments_checksum'] = $store->comments_checksum();
			}
			if ( in_array( 'post_meta_checksum', $fields_params, true ) ) {
				$checksums['post_meta_checksum'] = $store->post_meta_checksum();
			}
			if ( in_array( 'comment_meta_checksum', $fields_params, true ) ) {
				$checksums['comment_meta_checksum'] = $store->comment_meta_checksum();
			}

			if ( in_array( 'debug_details', $fields_params, true ) ) {
				$debug = self::get_debug_details();
			}
		}

		$full_sync_status = ( $sync_module ) ? $sync_module->get_status() : array();

		$full_queue = self::$sender->get_full_sync_queue();

		$result = array_merge(
			$full_sync_status,
			$checksums,
			$debug,
			array(
				'cron_size'            => count( $cron_timestamps ),
				'next_cron'            => $next_cron,
				'queue_size'           => $queue->size(),
				'queue_lag'            => $queue->lag(),
				'queue_next_sync'      => ( self::$sender->get_next_sync_time( 'sync' ) - microtime( true ) ),
				'full_queue_next_sync' => ( self::$sender->get_next_sync_time( 'full_sync' ) - microtime( true ) ),
			)
		);

		// Verify $sync_module is not false.
		if ( ( $sync_module ) && ! str_contains( get_class( $sync_module ), 'Full_Sync_Immediately' ) ) {
			$result['full_queue_size'] = $full_queue->size();
			$result['full_queue_lag']  = $full_queue->lag();
		}
		return $result;
	}

	/**
	 * Reset Sync locks.
	 *
	 * @access public
	 * @static
	 * @since 1.43.0
	 *
	 * @param bool $unlock_queues Whether to unlock Sync queues. Defaults to true.
	 */
	public static function reset_sync_locks( $unlock_queues = true ) {
		// Next sync locks.
		delete_option( Sender::NEXT_SYNC_TIME_OPTION_NAME . '_sync' );
		delete_option( Sender::NEXT_SYNC_TIME_OPTION_NAME . '_full_sync' );
		delete_option( Sender::NEXT_SYNC_TIME_OPTION_NAME . '_full-sync-enqueue' );
		// Retry after locks.
		delete_option( self::RETRY_AFTER_PREFIX . 'sync' );
		delete_option( self::RETRY_AFTER_PREFIX . 'full_sync' );
		// Dedicated sync locks.
		\Jetpack_Options::delete_raw_option( Dedicated_Sender::DEDICATED_SYNC_REQUEST_LOCK_OPTION_NAME );
		delete_transient( Dedicated_Sender::DEDICATED_SYNC_TEMPORARY_DISABLE_FLAG );

		// Queue locks.
		// Note that we are just unlocking the queues here, not reseting them.
		if ( $unlock_queues ) {
			$sync_queue = new Queue( 'sync' );
			$sync_queue->unlock();

			$full_sync_queue = new Queue( 'full_sync' );
			$full_sync_queue->unlock();
		}
	}
}