refactor: narrow vehicle stat repository contract

modules/services/vehicle-stat-service/src/main/java/com/lingniu/ingest/vehiclestat/JdbcVehicleStatMetricRepository.java

@@ -26,8 +26,7 @@ public final class JdbcVehicleStatMetricRepository implements VehicleStatReposit
         ensureSchema();
     }
 
-    @Override
+    private void saveDailyMileageMetric(VehicleDailyStatResult result) {
-    public void saveDailyStat(VehicleDailyStatResult result) {
         if (result == null || result.dailyMileageKm().isEmpty()) {
             return;
         }
@@ -88,7 +87,7 @@ public final class JdbcVehicleStatMetricRepository implements VehicleStatReposit
                 statDate,
                 OptionalDouble.of(dailyMileageKm),
                 DailyMileageStrategy.JT808_TOTAL_MILEAGE_DIFF);
-        saveDailyStat(result);
+        saveDailyMileageMetric(result);
         return Optional.of(result);
     }
 

modules/services/vehicle-stat-service/src/main/java/com/lingniu/ingest/vehiclestat/VehicleStatRepository.java

@@ -5,8 +5,6 @@ import java.util.Optional;
 
 public interface VehicleStatRepository {
 
-    void saveDailyStat(VehicleDailyStatResult result);
-
     Optional<VehicleDailyStatResult> recordDailyMileageSample(String vin, LocalDate statDate, double totalMileageKm);
 
     Optional<VehicleDailyStatResult> findDailyStat(String vin, LocalDate statDate);

modules/services/vehicle-stat-service/src/test/java/com/lingniu/ingest/vehiclestat/JdbcVehicleStatMetricRepositoryTest.java

@@ -5,30 +5,21 @@ import org.springframework.jdbc.core.JdbcTemplate;
 import org.springframework.jdbc.datasource.DriverManagerDataSource;
 
 import java.time.LocalDate;
-import java.util.OptionalDouble;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
 class JdbcVehicleStatMetricRepositoryTest {
 
     @Test
-    void upsertsDailyMileageIntoCommonMetricTable() {
+    void recordsDailyMileageIntoCommonMetricTable() {
         JdbcTemplate jdbcTemplate = new JdbcTemplate(new DriverManagerDataSource(
                 "jdbc:h2:mem:vehicle_stat_metric;MODE=MySQL;DATABASE_TO_LOWER=TRUE;DB_CLOSE_DELAY=-1",
                 "sa",
                 ""));
         JdbcVehicleStatMetricRepository repository = new JdbcVehicleStatMetricRepository(jdbcTemplate);
 
-        repository.saveDailyStat(new VehicleDailyStatResult(
+        repository.recordDailyMileageSample("VIN001", LocalDate.of(2026, 6, 30), 100.0);
-                "VIN001",
+        repository.recordDailyMileageSample("VIN001", LocalDate.of(2026, 6, 30), 115.5);
-                LocalDate.of(2026, 6, 30),
-                OptionalDouble.of(12.345),
-                DailyMileageStrategy.JT808_TOTAL_MILEAGE_DIFF));
-        repository.saveDailyStat(new VehicleDailyStatResult(
-                "VIN001",
-                LocalDate.of(2026, 6, 30),
-                OptionalDouble.of(15.5),
-                DailyMileageStrategy.JT808_TOTAL_MILEAGE_DIFF));
 
         assertThat(repository.findDailyStat("VIN001", LocalDate.of(2026, 6, 30)))
                 .isPresent()
@@ -36,12 +27,12 @@ class JdbcVehicleStatMetricRepositoryTest {
                 .extracting(result -> result.dailyMileageKm().orElseThrow())
                 .isEqualTo(15.5);
         assertThat(jdbcTemplate.queryForObject("SELECT COUNT(*) FROM vehicle_stat_metric", Integer.class))
-                .isEqualTo(1);
+                .isEqualTo(3);
         assertThat(jdbcTemplate.queryForObject(
-                "SELECT metric_key FROM vehicle_stat_metric WHERE vin = 'VIN001'",
+                "SELECT metric_key FROM vehicle_stat_metric WHERE vin = 'VIN001' AND metric_key = 'daily_mileage_km'",
                 String.class)).isEqualTo("daily_mileage_km");
         assertThat(jdbcTemplate.queryForObject(
-                "SELECT calculation_method FROM vehicle_stat_metric WHERE vin = 'VIN001'",
+                "SELECT calculation_method FROM vehicle_stat_metric WHERE vin = 'VIN001' AND metric_key = 'daily_mileage_km'",
                 String.class)).isEqualTo("JT808_TOTAL_MILEAGE_DIFF");
         assertThat(jdbcTemplate.queryForObject("""
                 SELECT COUNT(*)

modules/services/vehicle-stat-service/src/test/java/com/lingniu/ingest/vehiclestat/VehicleStatControllerTest.java

@@ -17,11 +17,8 @@ class VehicleStatControllerTest {
     @Test
     void returnsDailyStatJson() throws Exception {
         InMemoryVehicleStatRepository repository = new InMemoryVehicleStatRepository();
-        repository.saveDailyStat(new VehicleDailyStatResult(
+        repository.recordDailyMileageSample("VIN001", LocalDate.parse("2026-06-22"), 100.0);
-                "VIN001",
+        repository.recordDailyMileageSample("VIN001", LocalDate.parse("2026-06-22"), 135.5);
-                LocalDate.parse("2026-06-22"),
-                OptionalDouble.of(35.5),
-                DailyMileageStrategy.JT808_TOTAL_MILEAGE_DIFF));
         MockMvc mvc = standaloneSetup(new VehicleStatController(repository)).build();
 
         mvc.perform(get("/api/vehicle-stat/VIN001/daily").param("date", "2026-06-22"))
@@ -34,21 +31,19 @@ class VehicleStatControllerTest {
 
     private static final class InMemoryVehicleStatRepository implements VehicleStatRepository {
         private final java.util.Map<String, VehicleDailyStatResult> results = new java.util.HashMap<>();
-
+        private final java.util.Map<String, Double> firstTotals = new java.util.HashMap<>();
-        @Override
-        public void saveDailyStat(VehicleDailyStatResult result) {
-            results.put(result.vin() + ":" + result.statDate(), result);
-        }
 
         @Override
         public Optional<VehicleDailyStatResult> recordDailyMileageSample(String vin, LocalDate statDate,
                                                                          double totalMileageKm) {
+            String key = vin + ":" + statDate;
+            double firstTotal = firstTotals.computeIfAbsent(key, ignored -> totalMileageKm);
             VehicleDailyStatResult result = new VehicleDailyStatResult(
                     vin,
                     statDate,
-                    OptionalDouble.of(0.0),
+                    OptionalDouble.of(totalMileageKm - firstTotal),
                     DailyMileageStrategy.JT808_TOTAL_MILEAGE_DIFF);
-            saveDailyStat(result);
+            results.put(key, result);
             return Optional.of(result);
         }
 

modules/services/vehicle-stat-service/src/test/java/com/lingniu/ingest/vehiclestat/VehicleStatRepositoryContractTest.java

@@ -0,0 +1,18 @@
+package com.lingniu.ingest.vehiclestat;
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Method;
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class VehicleStatRepositoryContractTest {
+
+    @Test
+    void exposesOnlyMileageSampleAndQueryOperations() {
+        assertThat(Arrays.stream(VehicleStatRepository.class.getDeclaredMethods())
+                .map(Method::getName))
+                .containsExactlyInAnyOrder("recordDailyMileageSample", "findDailyStat");
+    }
+}

modules/services/vehicle-stat-service/src/test/java/com/lingniu/ingest/vehiclestat/jt808/Jt808MileageStreamProcessorTest.java

@@ -101,11 +101,6 @@ class Jt808MileageStreamProcessorTest {
         private final List<Double> samples = new ArrayList<>();
         private double firstSample = Double.NaN;
 
-        @Override
-        public void saveDailyStat(VehicleDailyStatResult result) {
-            results.add(result);
-        }
-
         @Override
         public Optional<VehicleDailyStatResult> recordDailyMileageSample(String vin, LocalDate statDate,
                                                                          double totalMileageKm) {