private function calculateTotalAmountForDeliveryExpenses(Transaction $transaction)
    {
        $total = 0;
        foreach ($transaction->getItems() as $productPurchase) {
            if($productPurchase->getProduct() instanceof Product){
                if(!$productPurchase->getProduct()->isFreeTransport()){
                    $addPercent = 0;
                    if($this->deliveryExpensesPercentage > 0) 
                        $addPercent = $productPurchase->getTotalPrice() * $this->deliveryExpensesPercentage;
                    
                    $total += $productPurchase->getTotalPrice() + $addPercent;
                }
            }else{
                $total += $productPurchase->getTotalPrice();
            }
        }
        return $total;
    }