Enhance Customer Update Functionality with Asynchronous Username Change Notification

- Added logic to send an asynchronous email notification when a customer's username is updated, improving user communication regarding account changes.
- Introduced a flag to track if the username has changed, ensuring notifications are only sent when necessary.
- Enhanced error handling and logging for successful customer updates, maintaining clarity in operational logs.

internal/customer/service.go

@@ -322,6 +322,7 @@ func (s *customerService) Update(ctx context.Context, id string, form *UpdateCus
 		return nil, errors.New("invalid username format")
 	}
 
+	changeUsername := false
 	// Check if username already exists (if changing username)
 	if form.Username != "" && strings.ToLower(form.Username) != customer.Username {
 		existingCustomer, _ := s.repository.GetByUsername(ctx, strings.ToLower(form.Username))
@@ -329,6 +330,7 @@ func (s *customerService) Update(ctx context.Context, id string, form *UpdateCus
 			return nil, errors.New("customer with this username already exists")
 		}
 		customer.Username = strings.ToLower(form.Username)
+		changeUsername = true
 	}
 
 	// Handle company assignments
@@ -366,6 +368,16 @@ func (s *customerService) Update(ctx context.Context, id string, form *UpdateCus
 		return nil, errors.New("failed to update customer")
 	}
 
+	if changeUsername {
+		go s.notification.SendEmail(context.Background(), notification.Model{
+			Recipient: customer.Email,
+			Title:     "Username Updated",
+			Message:   fmt.Sprintf("Your username has been updated to %s", customer.Username),
+			Type:      "info",
+			Priority:  "important",
+			UserID:    customer.ID.Hex(),
+		})
+	}
 	s.logger.Info("Customer updated successfully", map[string]interface{}{
 		"customer_id": customer.ID,
 		"email":       customer.Email,