core: Add CoreListener.on_event()

The `on_event()` method is called on all events. By default, it forwards the
event to the specific event handler methods. It's also a convenient method to
override if you want to handle all events in one place.

mopidy/core/listener.py

@@ -19,7 +19,20 @@ class CoreListener(object):
         """Helper to allow calling of core listener events"""
         listeners = pykka.ActorRegistry.get_by_class(CoreListener)
         for listener in listeners:
-            getattr(listener.proxy(), event)(**kwargs)
+            listener.proxy().on_event(event, **kwargs)
+
+    def on_event(self, event, **kwargs):
+        """
+        Called on all events.
+
+        *MAY* be implemented by actor. By default, this method forwards the
+        event to the specific event methods.
+
+        :param event: the event name
+        :type event: string
+        :param kwargs: any other arguments to the specific event handlers
+        """
+        getattr(self, event)(**kwargs)
 
     def track_playback_paused(self, track, time_position):
         """

tests/core/listener_test.py

@@ -1,5 +1,7 @@
 from __future__ import unicode_literals
 
+import mock
+
 from mopidy.core import CoreListener, PlaybackState
 from mopidy.models import Playlist, Track
 
@@ -10,6 +12,15 @@ class CoreListenerTest(unittest.TestCase):
     def setUp(self):
         self.listener = CoreListener()
 
+    def test_on_event_forwards_to_specific_handler(self):
+        self.listener.track_playback_paused = mock.Mock()
+
+        self.listener.on_event(
+            'track_playback_paused', track=Track(), position=0)
+
+        self.listener.track_playback_paused.assert_called_with(
+            track=Track(), position=0)
+
     def test_listener_has_default_impl_for_track_playback_paused(self):
         self.listener.track_playback_paused(Track(), 0)