public function prepare(Order $order)
    {
        /** @var $orderItems OrderItem[] */
        $orderItems = $order->orderItems;

        /** @var $newOrderItems OrderItem[] */
        $newOrderItems = array();

        foreach ($orderItems as $item) {
            if (!isset($newOrderItems[$item->getSKU()])) {
                $newOrderItems[$item->getSKU()] = $item;
            } else {
                $newOrderItems[$item->getSKU()]->setQuantity($newOrderItems[$item->getSKU()]->getQuantity() + $item->getQuantity());
                $newOrderItems[$item->getSKU()]->setTaxes($newOrderItems[$item->getSKU()]->getTaxes() + $item->getTaxes());
            }
        }

        $order->orderItems = $newOrderItems;

        return $order;
    }