Rename "active_detector" for background detecor. Improve thing selector coercion

src/openflexure_microscope_server/things/camera/__init__.py

@@ -28,6 +28,7 @@ from openflexure_microscope_server.things.background_detect import (
     BackgroundDetectAlgorithm,
 )
 from openflexure_microscope_server.ui import ActionButton, PropertyControl
+from openflexure_microscope_server.utilities import coerce_thing_selector
 
 
 class JPEGBlob(lt.blob.Blob):
@@ -158,7 +159,7 @@ class BaseCamera(lt.Thing):
     ``__init__`` method of the subclass.
     """
 
-    background_detectors: Mapping[str, BackgroundDetectAlgorithm] = lt.thing_slot()
+    _all_background_detectors: Mapping[str, BackgroundDetectAlgorithm] = lt.thing_slot()
 
     mjpeg_stream = lt.outputs.MJPEGStreamDescriptor()
     lores_mjpeg_stream = lt.outputs.MJPEGStreamDescriptor()
@@ -176,12 +177,17 @@ class BaseCamera(lt.Thing):
         # Default is never updated but is used if the value set from settings is
         # incorrect. In the future a better way to set defaults for thing slot mappings
         # would be ideal.
-        self._default_detector = "bg_channel_deviations_luv"
-        self._detector_name = "bg_channel_deviations_luv"
+        self._default_background_detector = "bg_channel_deviations_luv"
+        self._background_detector_name: Optional[str] = None
 
     def __enter__(self) -> Self:
         """Open hardware connection when the Thing context manager is opened."""
-        raise NotImplementedError("CameraThings must define their own __enter__ method")
+        self._background_detector_name = coerce_thing_selector(
+            thing_mapping=self._all_background_detectors,
+            selected=self._background_detector_name,
+            default=self._default_background_detector,
+        )
+        return self
 
     def __exit__(
         self,
@@ -190,7 +196,7 @@ class BaseCamera(lt.Thing):
         _traceback: Optional[TracebackType],
     ) -> None:
         """Close hardware connection when the Thing context manager is closed."""
-        raise NotImplementedError("CameraThings must define their own __exit__ method")
+        pass
 
     @lt.property
     def calibration_required(self) -> bool:
@@ -581,30 +587,31 @@ class BaseCamera(lt.Thing):
     # Note that the default detector name is set at init. This is over written if
     # setting is loaded from disk.
     @lt.setting
-    def detector_name(self) -> str:
+    def background_detector_name(self) -> Optional[str]:
         """The name of the active background selector."""
-        return self._detector_name
+        return self._background_detector_name
 
-    @detector_name.setter
-    def _set_detector_name(self, name: str) -> None:
-        """Validate and set detector_name."""
-        if name not in self.background_detectors:
+    @background_detector_name.setter
+    def _set_background_detector_name(self, name: str) -> None:
+        """Validate and set background_detector_name."""
+        if name not in self._all_background_detectors:
             self.logger.warning(f"{name} is not a valid background detector name.")
-        self._detector_name = name
+        self._background_detector_name = name
 
     @property
-    def active_detector(self) -> BackgroundDetectAlgorithm:
+    def background_detector(self) -> Optional[BackgroundDetectAlgorithm]:
         """The active background detector instance."""
-        if self.detector_name not in self.background_detectors:
-            self.logger.warning(f"No detector named {self.detector_name}")
-            self.detector_name = self._default_detector
-        return self.background_detectors[self.detector_name]
+        if self.background_detector_name is None:
+            return None
+        return self._all_background_detectors[self.background_detector_name]
 
     @lt.action
     def image_is_sample(self) -> tuple[bool, str]:
         """Label the current image as either background or sample."""
+        if self.background_detector is None:
+            raise RuntimeError("No background detectors available.")
         current_image = self.grab_as_array(stream_name="lores")
-        return self.active_detector.image_is_sample(current_image)
+        return self.background_detector.image_is_sample(current_image)
 
     @lt.action
     def set_background(self) -> None:
@@ -616,8 +623,10 @@ class BaseCamera(lt.Thing):
         future images to the distribution, to determine if each pixel is
         foreground or background.
         """
+        if self.background_detector is None:
+            raise RuntimeError("No background detectors available.")
         background = self.grab_as_array(stream_name="lores")
-        self.active_detector.set_background(background)
+        self.background_detector.set_background(background)
 
     @property
     def thing_state(self) -> Mapping[str, Any]: