public function willRefundCharge(PhabricatorUser $actor, PhortunePaymentProvider $provider, PhortuneCharge $charge, PhortuneCurrency $amount)
 {
     if (!$amount->isPositive()) {
         throw new Exception(pht('Trying to refund non-positive amount of money!'));
     }
     if ($amount->isGreaterThan($charge->getAmountRefundableAsCurrency())) {
         throw new Exception(pht('Trying to refund more money than remaining on charge!'));
     }
     if ($charge->getRefundedChargePHID()) {
         throw new Exception(pht('Trying to refund a refund!'));
     }
     if ($charge->getStatus() !== PhortuneCharge::STATUS_CHARGED && $charge->getStatus() !== PhortuneCharge::STATUS_HOLD) {
         throw new Exception(pht('Trying to refund an uncharged charge!'));
     }
     $refund_charge = PhortuneCharge::initializeNewCharge()->setAccountPHID($this->getAccount()->getPHID())->setCartPHID($this->getPHID())->setAuthorPHID($actor->getPHID())->setMerchantPHID($this->getMerchant()->getPHID())->setProviderPHID($provider->getProviderConfig()->getPHID())->setPaymentMethodPHID($charge->getPaymentMethodPHID())->setRefundedChargePHID($charge->getPHID())->setAmountAsCurrency($amount->negate());
     $charge->openTransaction();
     $charge->beginReadLocking();
     $copy = clone $charge;
     $copy->reload();
     if ($copy->getRefundingPHID() !== null) {
         throw new Exception(pht('Trying to refund a charge which is already refunding!'));
     }
     $refund_charge->save();
     $charge->setRefundingPHID($refund_charge->getPHID());
     $charge->save();
     $charge->endReadLocking();
     $charge->saveTransaction();
     return $refund_charge;
 }