Refactor UpdateRule method to handle category ID removal correctly.

internal/service/waf.go

@@ -817,11 +817,15 @@ func (s *wafService) UpdateRule(ctx context.Context, req *RuleRequest) error {
 			for i, id := range wafService.RuleCategoryStatus.CategoryID {
 				for _, categoryID := range req.CategoryID {
 					if id == categoryID {
+						if i == len(wafService.RuleCategoryStatus.CategoryID)-1 {
+							wafService.RuleCategoryStatus.CategoryID = wafService.RuleCategoryStatus.CategoryID[:i]
+						} else {
 							wafService.RuleCategoryStatus.CategoryID = append(wafService.RuleCategoryStatus.CategoryID[:i], wafService.RuleCategoryStatus.CategoryID[i+1:]...)
 						}
 					}
 				}
 			}
+		}
 
 		if err := s.db.Model(wafService).Update("rule_category_status", wafService.RuleCategoryStatus).Error; err != nil {
 			return fmt.Errorf("failed to update WAF service mode: %v", err)