fix: ignore invalid zero mileage metrics

go/vehicle-gateway/internal/stats/daily_metric.go

@@ -78,6 +78,9 @@ func SamplesFromEnvelope(env envelope.FrameEnvelope, loc *time.Location) ([]Metr
 	if !ok {
 		return nil, nil
 	}
+	if totalMileage <= 0 {
+		return nil, nil
+	}
 	if loc == nil {
 		loc = time.FixedZone("Asia/Shanghai", 8*3600)
 	}
@@ -115,14 +118,40 @@ INSERT INTO vehicle_daily_metric
    first_total_mileage_km, latest_total_mileage_km, sample_count, calculation_method)
 VALUES (?, ?, ?, ?, ?, 'km', ?, ?, 1, 'TOTAL_MILEAGE_DIFF')
 ON DUPLICATE KEY UPDATE
-  first_total_mileage_km = LEAST(first_total_mileage_km, VALUES(first_total_mileage_km)),
+  first_total_mileage_km = CASE
-  latest_total_mileage_km = GREATEST(latest_total_mileage_km, VALUES(latest_total_mileage_km)),
+    WHEN first_total_mileage_km IS NULL OR first_total_mileage_km <= 0
+      THEN VALUES(first_total_mileage_km)
+    ELSE LEAST(first_total_mileage_km, VALUES(first_total_mileage_km))
+  END,
+  latest_total_mileage_km = CASE
+    WHEN latest_total_mileage_km IS NULL OR latest_total_mileage_km <= 0
+      THEN VALUES(latest_total_mileage_km)
+    ELSE GREATEST(latest_total_mileage_km, VALUES(latest_total_mileage_km))
+  END,
   metric_value = CASE
     WHEN metric_key = 'daily_mileage_km'
-      THEN GREATEST(latest_total_mileage_km, VALUES(latest_total_mileage_km))
+      THEN GREATEST(
-           - LEAST(first_total_mileage_km, VALUES(first_total_mileage_km))
+             CASE
+               WHEN latest_total_mileage_km IS NULL OR latest_total_mileage_km <= 0
+                 THEN VALUES(latest_total_mileage_km)
+               ELSE latest_total_mileage_km
+             END,
+             VALUES(latest_total_mileage_km)
+           )
+           - CASE
+               WHEN first_total_mileage_km IS NULL OR first_total_mileage_km <= 0
+                 THEN VALUES(first_total_mileage_km)
+               ELSE LEAST(first_total_mileage_km, VALUES(first_total_mileage_km))
+             END
     WHEN metric_key = 'daily_total_mileage_km'
-      THEN GREATEST(latest_total_mileage_km, VALUES(latest_total_mileage_km))
+      THEN GREATEST(
+             CASE
+               WHEN latest_total_mileage_km IS NULL OR latest_total_mileage_km <= 0
+                 THEN VALUES(latest_total_mileage_km)
+               ELSE latest_total_mileage_km
+             END,
+             VALUES(latest_total_mileage_km)
+           )
     ELSE VALUES(metric_value)
   END,
   sample_count = sample_count + 1,

go/vehicle-gateway/internal/stats/daily_metric_test.go

@@ -64,6 +64,25 @@ func TestSamplesFromEnvelopeSkipsMissingVINOrMileage(t *testing.T) {
 	}
 }
 
+func TestSamplesFromEnvelopeSkipsNonPositiveMileage(t *testing.T) {
+	for _, value := range []any{0, 0.0, -1.0, "0"} {
+		samples, err := SamplesFromEnvelope(envelope.FrameEnvelope{
+			Protocol:    envelope.ProtocolJT808,
+			VIN:         "LNBVIN00000000001",
+			EventTimeMS: time.Date(2026, 7, 1, 9, 0, 0, 0, time.FixedZone("Asia/Shanghai", 8*3600)).UnixMilli(),
+			Fields: map[string]any{
+				envelope.FieldTotalMileageKM: value,
+			},
+		}, nil)
+		if err != nil {
+			t.Fatalf("SamplesFromEnvelope(%#v) error = %v", value, err)
+		}
+		if len(samples) != 0 {
+			t.Fatalf("expected no samples for non-positive mileage %#v, got %#v", value, samples)
+		}
+	}
+}
+
 func TestWriterEnsuresSchemaAndUpsertsTwoMetrics(t *testing.T) {
 	exec := &recordingExec{}
 	writer := NewWriter(exec, time.FixedZone("Asia/Shanghai", 8*3600))
@@ -90,6 +109,9 @@ func TestWriterEnsuresSchemaAndUpsertsTwoMetrics(t *testing.T) {
 	if !strings.Contains(exec.calls[1].query, "ON DUPLICATE KEY UPDATE") {
 		t.Fatalf("unexpected upsert sql: %s", exec.calls[1].query)
 	}
+	if !strings.Contains(exec.calls[1].query, "first_total_mileage_km <= 0") {
+		t.Fatalf("upsert should ignore legacy zero first mileage: %s", exec.calls[1].query)
+	}
 }
 
 type execCall struct {