static function calculate(S $s, $k = null, $kType = 'waitPeriodType') {
		$k = $k ?: df_caller_f(); /** @type string */
		return dfcf(function(S $s, $k, $kType) {
			$r = $s->nat($k); /** @var int $r */
			return self::$WORKING_DAYS === $s->v($kType) ? $r :
				df_num_calendar_days_by_num_working_days(ZD::now(), $r, $s->scope())
			;
		}, [$s, $k, $kType]);
	}