public function getOrderPeriodFirstDay($day)
    {

        $currentWeekday = $this->formatAsWeekday($day);
        $dateDiff = 7 - $this->getSendOrderListsWeekday() + $currentWeekday;
        $date = strtotime('-' . $dateDiff . ' day ', $day);

        if ($currentWeekday > $this->getDeliveryWeekday()) {
            $date = strtotime('+7 day', $date);
        }

        $date = date($this->getI18Format('DateShortAlt'), $date);

        return $date;
    }