public function add($param)
{
$value = Sanitize::integer($param);
$param = Sanitize::letters($param);
$hour = $this->getHours();
$minute = $this->getMinutes();
$second = $this->getSeconds();
$month = $this->getMonth();
$day = $this->getDay();
$year = $this->getYear();
switch ($param) {
case 'y':
$year += $value;
break;
case 'm':
$month += $value;
break;
case 'd':
$day += $value;
break;
case 'h':
$hour += $value;
break;
case 'i':
$minute += $value;
break;
case 's':
$second += $value;
break;
default:
break;
}
$this->changeDate(date('Y-m-d H:i:s', mktime($hour, $minute, $second, $month, $day, $year)));
}
