Fix refund loading

src/main/java/org/example/petshopdesktop/controllers/dialogcontrollers/RefundDialogController.java

@@ -19,9 +19,12 @@ import java.math.BigDecimal;
 import java.text.NumberFormat;
 import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
 import java.util.Optional;
+import java.util.stream.Collectors;
 
 public class RefundDialogController {
 
@@ -127,15 +130,10 @@ public class RefundDialogController {
 
         try {
             List<SaleResponse> allSales = SaleApi.getInstance().listSales(0, 1000, null);
-            boolean alreadyRefunded = allSales.stream()
-                .anyMatch(s -> Boolean.TRUE.equals(s.getIsRefund()) && saleId.equals(s.getOriginalSaleId()));
-
-            if (alreadyRefunded) {
-                showError("Load Sale", "This sale has already been refunded.");
-                return;
-            }
-
             currentSale = SaleApi.getInstance().getSale(saleId);
+            List<SaleResponse> previousRefunds = allSales.stream()
+                .filter(s -> Boolean.TRUE.equals(s.getIsRefund()) && saleId.equals(s.getOriginalSaleId()))
+                .collect(Collectors.toList());
 
             DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
             String saleInfo = String.format("Sale Date: %s | Employee: %s | Original Total: %s | Payment: %s",
@@ -145,7 +143,13 @@ public class RefundDialogController {
                 currentSale.getPaymentMethod());
             lblSaleInfo.setText(saleInfo);
 
-            tvOriginalItems.setItems(FXCollections.observableArrayList(currentSale.getItems()));
+            List<SaleItemResponse> refundableItems = buildRefundableItems(currentSale, previousRefunds);
+            if (refundableItems.isEmpty()) {
+                showError("Load Sale", "This sale has no remaining refundable items.");
+                return;
+            }
+
+            tvOriginalItems.setItems(FXCollections.observableArrayList(refundableItems));
             cbPaymentMethod.getSelectionModel().select(currentSale.getPaymentMethod());
 
             refundItems.clear();
@@ -303,6 +307,47 @@ public class RefundDialogController {
         stage.close();
     }
 
+    private List<SaleItemResponse> buildRefundableItems(SaleResponse sale, List<SaleResponse> previousRefunds) {
+        Map<Long, Integer> refundedByProduct = new HashMap<>();
+        for (SaleResponse refund : previousRefunds) {
+            if (refund.getItems() == null) {
+                continue;
+            }
+            for (SaleItemResponse refundItem : refund.getItems()) {
+                if (refundItem.getProdId() == null || refundItem.getQuantity() == null) {
+                    continue;
+                }
+                refundedByProduct.merge(refundItem.getProdId(), Math.abs(refundItem.getQuantity()), Integer::sum);
+            }
+        }
+
+        List<SaleItemResponse> refundableItems = new ArrayList<>();
+        if (sale.getItems() == null) {
+            return refundableItems;
+        }
+
+        for (SaleItemResponse originalItem : sale.getItems()) {
+            if (originalItem.getProdId() == null || originalItem.getQuantity() == null) {
+                continue;
+            }
+
+            int remainingQuantity = originalItem.getQuantity() - refundedByProduct.getOrDefault(originalItem.getProdId(), 0);
+            if (remainingQuantity <= 0) {
+                continue;
+            }
+
+            SaleItemResponse refundableItem = new SaleItemResponse();
+            refundableItem.setSaleItemId(originalItem.getSaleItemId());
+            refundableItem.setProdId(originalItem.getProdId());
+            refundableItem.setProductName(originalItem.getProductName());
+            refundableItem.setQuantity(remainingQuantity);
+            refundableItem.setUnitPrice(originalItem.getUnitPrice());
+            refundableItems.add(refundableItem);
+        }
+
+        return refundableItems;
+    }
+
     private void showError(String title, String message) {
         Alert alert = new Alert(Alert.AlertType.ERROR);
         alert.setTitle(title);