Add grouping by outlet_id

internal/service/analytics_service.go

@@ -196,10 +196,11 @@ func (s *AnalyticsServiceImpl) validatePurchasingAnalyticsRequest(req *models.Pu
 
 	if req.GroupBy != "" {
 		validGroupBy := map[string]bool{
-			"day":   true,
-			"hour":  true,
-			"week":  true,
-			"month": true,
+			"day":       true,
+			"hour":      true,
+			"week":      true,
+			"month":     true,
+			"outlet_id": true,
 		}
 		if !validGroupBy[req.GroupBy] {
 			return fmt.Errorf("invalid group_by value: %s", req.GroupBy)

internal/service/analytics_service_test.go

@@ -132,6 +132,21 @@ func TestAnalyticsServiceGetPurchasingAnalyticsAllowsEmptyGroupBy(t *testing.T)
 	require.NotNil(t, resp)
 }
 
+func TestAnalyticsServiceGetPurchasingAnalyticsAllowsOutletGroupBy(t *testing.T) {
+	service := NewAnalyticsServiceImpl(analyticsProcessorStub{})
+	now := time.Date(2026, 5, 1, 0, 0, 0, 0, time.UTC)
+
+	resp, err := service.GetPurchasingAnalytics(context.Background(), &models.PurchasingAnalyticsRequest{
+		OrganizationID: uuid.New(),
+		DateFrom:       now,
+		DateTo:         now,
+		GroupBy:        "outlet_id",
+	})
+
+	require.NoError(t, err)
+	require.NotNil(t, resp)
+}
+
 func TestAnalyticsServiceGetProfitLossAnalyticsValidation(t *testing.T) {
 	service := NewAnalyticsServiceImpl(analyticsProcessorStub{})
 	now := time.Date(2026, 5, 1, 0, 0, 0, 0, time.UTC)