public function getDiscountAmount()
    {
        $total = 0;
        $discount = 0;
        
        foreach ($this->items as $item) {
            if ($item->Price) {
                $total += ($item->Price * $item->Quantity);
            }
            
            if ($item->Discount) {
                $discount += ($item->TotalDiscount);
            }
        }
        
        if ($discount > $total) {
            $discount = $total;
        }

        return $discount;
    }