Fix optional-discharge crashes and dedupe measurement mapping

- MeasurementResponse.discharge is now Optional[float]; measurements with a
  null discharge no longer raise a Pydantic ValidationError (HTTP 500) on the
  /measurements/latest and /measurements/station endpoints.
- InfluxDB save_measurements guards float(discharge) against None instead of
  crashing with TypeError.
- Extract the duplicated measurement->response mapping into a single
  _to_measurement_response helper used by both measurement endpoints.

src/database_adapters.py

@@ -111,9 +111,11 @@ class InfluxDBAdapter(DatabaseAdapter):
                     "time": measurement["timestamp"].isoformat(),
                     "fields": {
                         "water_level": float(measurement["water_level"]),
-                        "discharge": float(measurement["discharge"]),
+                        "discharge": float(measurement["discharge"])
+                        if measurement.get("discharge") is not None
+                        else None,
                         "discharge_percent": float(measurement["discharge_percent"])
-                        if measurement["discharge_percent"]
+                        if measurement.get("discharge_percent")
                         else None,
                     },
                 }

src/web_api.py

@@ -59,7 +59,7 @@ class MeasurementResponse(BaseModel):
     station_name_en: str
     station_name_th: str
     water_level: float
-    discharge: float
+    discharge: Optional[float] = None
     discharge_percent: Optional[float] = None
     status: str = "active"
 
@@ -478,6 +478,24 @@ async def get_station(station_id: int):
     )
 
 
+def _to_measurement_response(measurement: Dict[str, Any]) -> MeasurementResponse:
+    """Map a raw measurement dict from a DB adapter to the API response model.
+
+    ``discharge`` is optional in the data (some stations report only level), so
+    it is read with ``.get`` rather than assumed present.
+    """
+    return MeasurementResponse(
+        timestamp=measurement["timestamp"],
+        station_code=measurement["station_code"],
+        station_name_en=measurement["station_name_en"],
+        station_name_th=measurement["station_name_th"],
+        water_level=measurement["water_level"],
+        discharge=measurement.get("discharge"),
+        discharge_percent=measurement.get("discharge_percent"),
+        status=measurement.get("status", "active"),
+    )
+
+
 @app.get("/measurements/latest", response_model=List[MeasurementResponse])
 async def get_latest_measurements(limit: int = 100):
     """Get latest measurements from all stations"""
@@ -490,22 +508,7 @@ async def get_latest_measurements(limit: int = 100):
     try:
         measurements = scraper.get_latest_data(limit=limit)
 
-        response = []
-        for measurement in measurements:
-            response.append(
-                MeasurementResponse(
-                    timestamp=measurement["timestamp"],
-                    station_code=measurement["station_code"],
-                    station_name_en=measurement["station_name_en"],
-                    station_name_th=measurement["station_name_th"],
-                    water_level=measurement["water_level"],
-                    discharge=measurement["discharge"],
-                    discharge_percent=measurement.get("discharge_percent"),
-                    status=measurement.get("status", "active"),
-                )
-            )
-
-        return response
+        return [_to_measurement_response(m) for m in measurements]
 
     except Exception as e:
         logger.error(f"Error fetching latest measurements: {e}")
@@ -533,22 +536,7 @@ async def get_station_measurements(station_code: str, hours: int = 24, limit: in
         # Limit results
         measurements = measurements[:limit]
 
-        response = []
-        for measurement in measurements:
-            response.append(
-                MeasurementResponse(
-                    timestamp=measurement["timestamp"],
-                    station_code=measurement["station_code"],
-                    station_name_en=measurement["station_name_en"],
-                    station_name_th=measurement["station_name_th"],
-                    water_level=measurement["water_level"],
-                    discharge=measurement["discharge"],
-                    discharge_percent=measurement.get("discharge_percent"),
-                    status=measurement.get("status", "active"),
-                )
-            )
-
-        return response
+        return [_to_measurement_response(m) for m in measurements]
 
     except Exception as e:
         logger.error(f"Error fetching station measurements: {e}")