Week::calculate

public function calculate()
{
	if (empty($this->type))
	{
		return $this->startDate;
	}

	if ($this->type === self::TYPE_A_FEW_WEEKS_BEFORE || $this->type === self::TYPE_A_FEW_WEEKS_AFTER)
	{
		return $this->calculateAlternatingWeeks();
	}
	else
	{
		return $this->calculateAlternatingWithDays();
	}
}