ACP2E-793: Discount value is incorrect in GraphQL response

Author: glo23503

app/code/Magento/SalesRule/Model/Rule/Action/Discount/ByFixed.php

@@ -22,11 +22,13 @@ public function calculate($rule, $item, $qty)
 
         $baseDiscountAmount = (float) $rule->getDiscountAmount();
         $discountAmount = $this->priceCurrency->convert($baseDiscountAmount, $item->getQuote()->getStore());
+        $itemDiscountAmount = $item->getDiscountAmount();
+        $itemBaseDiscountAmount = $item->getBaseDiscountAmount();
         $itemPrice = $this->validator->getItemPrice($item);
         $baseItemPrice = $this->validator->getItemBasePrice($item);
 
-        $discountAmountMin = min($itemPrice * $qty, $discountAmount * $qty);
-        $baseDiscountAmountMin = min($baseItemPrice * $qty, $baseDiscountAmount * $qty);
+        $discountAmountMin = min(($itemPrice * $qty) - $itemDiscountAmount, $discountAmount * $qty);
+        $baseDiscountAmountMin = min(($baseItemPrice * $qty) - $itemBaseDiscountAmount, $baseDiscountAmount * $qty);
 
         $discountData->setAmount($discountAmountMin);
         $discountData->setBaseAmount($baseDiscountAmountMin);