Calculator::calculateDate

public function calculateDate()
{
	$period = $this->params[self::FIELD_PERIOD_NAME];
	$startDate = clone($this->startDate);
	switch($period)
	{
		case static::SALE_TYPE_DAY_OFFSET:
			return DateType\Day::calculateDate($this->params, $startDate);
		case static::SALE_TYPE_WEEK_OFFSET:
			return DateType\Week::calculateDate($this->params, $startDate);
		case static::SALE_TYPE_MONTH_OFFSET:
			return DateType\Month::calculateDate($this->params, $startDate);
		case static::SALE_TYPE_YEAR_OFFSET:
			return DateType\Year::calculateDate($this->params, $startDate);
		default:
			return null;
	}
}