Implement discounts in magento 1.9 with magento wallet functionality - magento

Question

I am have implemented custom discounts in magento which is working properly.But, when discount is implemented and someone is trying to pay from magento wallet balance, wallet seems to stop working and the amount paid from wallet does not get deducted from the grand total of the cart.
Discount is applied as follows:
config.xml-
<sales>
<quote>
<totals>
<discount>
<class>Uf_Rewards_Model_Discount</class>
<after>subtotal</after>
</discount>
</totals>
</quote>
</sales>
Discount.php:
class Uf_Rewards_Model_Discount extends Mage_SalesRule_Model_Quote_Discount {
public function collect(Mage_Sales_Model_Quote_Address $address) {
if ($address->getData('address_type') == 'billing')
return $this;
$discount = 10; //your discount percent
$grandTotal = $address->getGrandTotal();
$baseGrandTotal = $address->getBaseGrandTotal();
$totals = array_sum($address->getAllTotalAmounts());
$baseTotals = array_sum($address->getAllBaseTotalAmounts());
$address->setFeeAmount(-$discount);
$address->setBaseFeeAmount(-$discount);
$address->setGrandTotal($grandTotal + $address->getFeeAmount());
$address->setBaseGrandTotal($baseGrandTotal + $address->getBaseFeeAmount());
$address->setDiscountAmount(-$discount);
$address->setBaseDiscountAmount(-$discount);
return $this;
}
public function fetch(Mage_Sales_Model_Quote_Address $address) {
if ($address->getData('address_type') == 'billing')
return $this;
$amt = $address->getFeeAmount();
// $amt=300;
if ($amt != 0) {
Mage::log($amt, NULL, 'obsrvr.log');
$address->addTotal(array(
'code' => 'Discount',
'title' => 'Discount',
'value' => $amt
));
}
return $this;
}
}