}

	/**
	 * Dispatches the bg updater
	 *
	 * @since 3.4.3
	 *
	 * @return void
	 */
	public static function dispatch_db_updates() {
		self::$background_updater->save()->dispatch();
	}

	/**
	 * Retrieve the default difficulty terms that should be created on a fresh install
	 *
	 * @since 3.3.1
	 *
	 * @return array
	 */
	public static function get_difficulties() {
		return apply_filters(
			'llms_install_create_difficulties',
			array(
				_x( 'Beginner', 'course difficulty name', 'lifterlms' ),
				_x( 'Intermediate', 'course difficulty name', 'lifterlms' ),
				_x( 'Advanced', 'course difficulty name', 'lifterlms' ),
			)
		);
	}

	/**
	 * Get a string of table data that can be passed to dbDelta() to install LLMS tables
	 *
	 * @since 3.0.0
	 * @since 3.16.9 Unknown
	 * @since 3.16.9 Unknown
	 * @since 3.34.0 Added `llms_install_get_schema` filter to method return.
	 * @since 3.36.0 Added `wp_lifterlms_events` table.
	 * @since 4.0.0 Added `wp_lifterlms_sessions` table.
	 * @since 4.5.0 Added `wp_lifterlms_events_open_sessions` table.
	 *
	 * @return string
	 */
	private static function get_schema() {

		global $wpdb;

		$collate = '';

		if ( $wpdb->has_cap( 'collation' ) ) {

			if ( ! empty( $wpdb->charset ) ) {
				$collate .= "DEFAULT CHARACTER SET $wpdb->charset";
			}
			if ( ! empty( $wpdb->collate ) ) {
				$collate .= " COLLATE $wpdb->collate";
			}
		}

		$tables = "
CREATE TABLE `{$wpdb->prefix}lifterlms_user_postmeta` (
  meta_id bigint(20) NOT NULL auto_increment,
  user_id bigint(20) NOT NULL,
  post_id bigint(20) NOT NULL,
  meta_key varchar(255) NULL,
  meta_value longtext NULL,
  updated_date datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  PRIMARY KEY (`meta_id`),
  KEY user_id (`user_id`),
  KEY post_id (`post_id`)
) $collate;
CREATE TABLE `{$wpdb->prefix}lifterlms_quiz_attempts` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `student_id` bigint(20) DEFAULT NULL,
  `quiz_id` bigint(20) DEFAULT NULL,
  `lesson_id` bigint(20) DEFAULT NULL,
  `start_date` datetime DEFAULT NULL,
  `update_date` datetime DEFAULT NULL,
  `end_date` datetime DEFAULT NULL,
  `status` varchar(15) DEFAULT '',
  `attempt` bigint(20) DEFAULT NULL,
  `grade` float DEFAULT NULL,
  `questions` longtext,
  PRIMARY KEY (`id`),
  KEY `student_id` (`student_id`),
  KEY `quiz_id` (`quiz_id`)
) $collate;
CREATE TABLE `{$wpdb->prefix}lifterlms_product_to_voucher` (
  `product_id` bigint(20) NOT NULL,
  `voucher_id` bigint(20) NOT NULL,
  KEY `product_id` (`product_id`),
  KEY `voucher_id` (`voucher_id`)
) $collate;
CREATE TABLE `{$wpdb->prefix}lifterlms_voucher_code_redemptions` (
  `id` int(20) unsigned NOT NULL AUTO_INCREMENT,
  `code_id` bigint(20) NOT NULL,
  `user_id` bigint(20) NOT NULL,
  `redemption_date` datetime DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `code_id` (`code_id`),
  KEY `user_id` (`user_id`)
) $collate;
CREATE TABLE `{$wpdb->prefix}lifterlms_vouchers_codes` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `voucher_id` bigint(20) NOT NULL,
  `code` varchar(20) NOT NULL DEFAULT '',
  `redemption_count` bigint(20) DEFAULT NULL,
  `is_deleted` tinyint(1) NOT NULL DEFAULT '0',
  `created_at` datetime DEFAULT NULL,
  `updated_at` datetime DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `code` (`code`),
  KEY `voucher_id` (`voucher_id`)
) $collate;
CREATE TABLE `{$wpdb->prefix}lifterlms_notifications` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `created` datetime DEFAULT NULL,
  `updated` datetime DEFAULT NULL,
  `status` varchar(11) DEFAULT '0',
  `type` varchar(75) DEFAULT NULL,
  `subscriber` varchar(255) DEFAULT NULL,
  `trigger_id` varchar(75) DEFAULT NULL,
  `user_id` bigint(20) DEFAULT NULL,
  `post_id` bigint(20) DEFAULT NULL,