Update milk tea redeem dialog and notifications

src/main/java/com/openisle/service/ActivityService.java

@@ -39,10 +39,7 @@ public class ActivityService {
 
     public void redeem(Activity activity, User user, String contact) {
         String content = user.getUsername() + " contact: " + contact;
-        for (User admin : userRepository.findByRole(Role.ADMIN)) {
-            notificationService.createNotification(admin, NotificationType.ACTIVITY_REDEEM,
-                    null, null, null, user, null, content);
-        }
+        notificationService.createActivityRedeemNotifications(user, content);
         activity.getParticipants().add(user);
         activityRepository.save(activity);
     }

src/main/java/com/openisle/service/NotificationService.java

@@ -46,6 +46,19 @@ public class NotificationService {
         }
     }
 
+    /**
+     * Create notifications for all admins when a user redeems an activity.
+     * Old redeem notifications from the same user are removed first.
+     */
+    @org.springframework.transaction.annotation.Transactional
+    public void createActivityRedeemNotifications(User user, String content) {
+        notificationRepository.deleteByTypeAndFromUser(NotificationType.ACTIVITY_REDEEM, user);
+        for (User admin : userRepository.findByRole(Role.ADMIN)) {
+            createNotification(admin, NotificationType.ACTIVITY_REDEEM, null, null,
+                    null, user, null, content);
+        }
+    }
+
     public List<Notification> listNotifications(String username, Boolean read) {
         User user = userRepository.findByUsername(username)
                 .orElseThrow(() -> new com.openisle.exception.NotFoundException("User not found"));

src/test/java/com/openisle/service/NotificationServiceTest.java

@@ -96,4 +96,23 @@ class NotificationServiceTest {
         verify(nRepo).deleteByTypeAndFromUser(NotificationType.REGISTER_REQUEST, applicant);
         verify(nRepo).save(any(Notification.class));
     }
+
+    @Test
+    void createActivityRedeemNotificationsDeletesOldOnes() {
+        NotificationRepository nRepo = mock(NotificationRepository.class);
+        UserRepository uRepo = mock(UserRepository.class);
+        NotificationService service = new NotificationService(nRepo, uRepo);
+
+        User admin = new User();
+        admin.setId(10L);
+        User user = new User();
+        user.setId(20L);
+
+        when(uRepo.findByRole(Role.ADMIN)).thenReturn(List.of(admin));
+
+        service.createActivityRedeemNotifications(user, "contact");
+
+        verify(nRepo).deleteByTypeAndFromUser(NotificationType.ACTIVITY_REDEEM, user);
+        verify(nRepo).save(any(Notification.class));
+    }
 }