fix: shortlink generation logic update/create

internal/api/service/shortlink_service.go

@@ -94,6 +94,31 @@ func (s *ShortLinkService) GenerateShortLink(req *models.GenerateShortLinkReques
 		return nil, errors.New("invalid date of birth format, expected YYYY-MM-DD")
 	}
 
+	// Check if an unexpired shortlink already exists for this patient and study
+	existingShortLink, err := s.shortLinkRepo.GetActiveShortLinkByPatientAndStudy(req.PatientID, req.StudyUID)
+	if err != nil {
+		s.logger.Error("Error checking for existing shortlinks", zap.Error(err))
+		return nil, ErrCreationFailed
+	}
+
+	// If an active shortlink exists, return it instead of creating a new one
+	if existingShortLink != nil {
+		s.logger.Info("Returning existing active shortlink",
+			zap.String("patientID", req.PatientID),
+			zap.String("studyUID", req.StudyUID),
+			zap.String("token", existingShortLink.Token))
+
+		// Generate the full URL using the configured base URL
+		fullURL := fmt.Sprintf("%s/short-auth?short=%s", s.baseURL, existingShortLink.Token)
+
+		return &models.GenerateShortLinkResponse{
+			ShortToken: existingShortLink.Token,
+			FullURL:    fullURL,
+			ExpiresAt:  existingShortLink.ExpiresAt,
+			IsExisting: true,
+		}, nil
+	}
+
 	// Set expiration if not provided
 	expiresIn := s.defaultExpiryTime
 	if req.ExpiresIn > 0 {
@@ -139,6 +164,7 @@ func (s *ShortLinkService) GenerateShortLink(req *models.GenerateShortLinkReques
 		ShortToken: token,
 		FullURL:    fullURL,
 		ExpiresAt:  shortLink.ExpiresAt,
+		IsExisting: false,
 	}, nil
 }