Add validation for having pending operations while app installation

components/application-mgt/io.entgra.device.mgt.core.application.mgt.core/src/main/java/io/entgra/device/mgt/core/application/mgt/core/impl/SubscriptionManagerImpl.java

@@ -180,6 +180,7 @@ public class SubscriptionManagerImpl implements SubscriptionManager {
         ApplicationDTO applicationDTO = getApplicationDTO(applicationUUID);
         ApplicationSubscriptionInfo applicationSubscriptionInfo = getAppSubscriptionInfo(applicationDTO, subType,
                 params);
+        validatePendingAppSubscription(applicationSubscriptionInfo, applicationDTO);
         performExternalStoreSubscription(applicationDTO, applicationSubscriptionInfo);
         ApplicationInstallResponse applicationInstallResponse = performActionOnDevices(
                 applicationSubscriptionInfo.getAppSupportingDeviceTypeName(), applicationSubscriptionInfo.getDevices(),
@@ -707,6 +708,37 @@ public class SubscriptionManagerImpl implements SubscriptionManager {
         }
     }
 
+    private <T> void validatePendingAppSubscription(ApplicationSubscriptionInfo applicationSubscriptionInfo, ApplicationDTO applicationDTO) throws BadRequestException, ApplicationManagementException{
+        int tenantId = PrivilegedCarbonContext.getThreadLocalCarbonContext().getTenantId(true);
+        int applicationReleaseId = applicationDTO.getApplicationReleaseDTOs().get(0).getId();
+        try {
+            List<DeviceSubscriptionDTO> deviceSubscriptionDTOS = subscriptionDAO
+                    .getDeviceSubscriptions(applicationReleaseId, tenantId, null, null);
+            List<Integer> deviceIdList = new ArrayList<>();
+            deviceSubscriptionDTOS.forEach(deviceSubscriptionDTO -> {
+                if (!deviceSubscriptionDTO.isUnsubscribed() &&
+                        Operation.Status.PENDING.toString().equalsIgnoreCase(deviceSubscriptionDTO.getStatus())) {
+                    deviceIdList.add(deviceSubscriptionDTO.getDeviceId());
+                }
+            });
+
+            List<Integer> subscriptionDeviceIds = applicationSubscriptionInfo.getDevices().stream()
+                    .map(Device::getId)
+                    .collect(Collectors.toList());
+            boolean allDevicesPending = subscriptionDeviceIds.stream()
+                    .allMatch(deviceIdList::contains);
+            if (allDevicesPending) {
+                String msg = "All devices in the subscription have pending operations for this application.";
+                log.error(msg);
+                throw new BadRequestException(msg);
+            }
+        } catch (ApplicationManagementDAOException e) {
+            String msg = "Error while retrieving device subscriptions";
+            log.error(msg, e);
+            throw new ApplicationManagementException("Error while validating application subscription", e);
+        }
+    }
+
     /**
      * This method perform given action (i.e APP INSTALL or APP UNINSTALL) on given set of devices.
      *