Rework lidar cache to support grpc streaming

pycar/src/car/tracking/lidar_cache.py

@@ -10,7 +10,7 @@ import time
 class LidarCache():
     """
     A class that retrieves scans from the lidar,
-    runs grouping algorithms between scans and 
+    runs grouping algorithms on the scans and 
     keeps a copy of the group data.
     """
 
@@ -56,16 +56,10 @@ class LidarCache():
             else:
                 self.currentGroups = algorithms.calc_groups(scan)
 
-            self.fireGroupsChanged()
+            self._fireGroupsChanged()
 
-    def fireGroupsChanged(self):
-        # Send the updated groups to 0MQ socket.
-        # Rename this to be a generic listener method, rather than an explicit 'send' (even though it can be treated as such already)
-        pointScan = tracker_pb.PointScan()
-        for group in self.currentGroups:
-            for point in group.get_points():
-                pointScan.points.append(tracker_pb.Point(
-                    angle=point[1], distance=point[2], group_number=group.number))
+    def _fireGroupsChanged(self):
+        pointScan = self.current_scan
 
         for listener in self._group_listeners:
             listener(pointScan)
@@ -81,15 +75,33 @@ class LidarCache():
         listener
             An function that takes a PointScan proto object as its argument.
         """
-        self._group_listeners.append(listener)
+        if(listener not in self._group_listeners):
+            self._group_listeners.append(listener)
+
+    def clear_listeners(self):
+        """
+        Clear all group change listeners.
+        """
+        self._group_listeners = []
+
+    @property
+    def current_scan(self):
+        pointScan = tracker_pb.PointScan()
+        for group in self.currentGroups:
+            for point in group.get_points():
+                pointScan.points.append(tracker_pb.Point(
+                    angle=point[1], distance=point[2], group_number=group.number))
+        return pointScan
 
     def stop_scanning(self):
         self.run = False
 
+
 if __name__ == '__main__':
-    lidar = MockLidar(iter(lidar_loader.load_scans_bytes_file('car/src/car/tracking/out.pickle')))
+    lidar = MockLidar(iter(lidar_loader.load_scans_bytes_file(
+        'car/src/car/tracking/out.pickle')))
     cache = LidarCache(lidar)
-    cache.add_groups_changed_listener(lambda a : print(a))
+    cache.add_groups_changed_listener(lambda a: print(a))
     cache.start_cache()
     time.sleep(1)
     cache.stop_scanning()