add fallback model

my/location/fallback/common.py

@@ -0,0 +1,33 @@
+from dataclasses import dataclass
+from typing import Optional
+from datetime import datetime, timedelta
+
+from ..common import Location
+
+
+@dataclass
+class FallbackLocation:
+    lat: float
+    lon: float
+    dt: datetime
+    duration: int  # time in seconds for how long this is valid
+    accuracy: Optional[float] = None
+    elevation: Optional[float] = None
+    datasource: Optional[str] = None  # which module provided this, useful for debugging
+
+    def to_location(self, end: bool = False) -> Location:
+        """
+        by default the start date is used for the location
+        If end is True, the start date + duration is used
+        """
+        dt: datetime = self.dt
+        if end:
+            dt += timedelta(self.duration)
+        return Location(
+            lat=self.lat,
+            lon=self.lon,
+            dt=dt,
+            accuracy=self.accuracy,
+            elevation=self.elevation,
+            datasource=self.datasource,
+        )