/**
* Prepare invoice data for refund
*
* @param \Magento\Sales\Model\Order\Creditmemo $creditmemo
* @return void
*/
protected function prepareInvoice(\Magento\Sales\Model\Order\Creditmemo $creditmemo)
{
if ($creditmemo->getInvoice()) {
$creditmemo->getInvoice()->setIsUsedForRefund(true);
$creditmemo->getInvoice()->setBaseTotalRefunded($creditmemo->getInvoice()->getBaseTotalRefunded() + $creditmemo->getBaseGrandTotal());
$creditmemo->setInvoiceId($creditmemo->getInvoice()->getId());
}
}