mpd: Trigger 'output' idle event on mute_changed()

This is required for e.g. ncmpcpp to detect that an enableoutput/disableoutput
command worked, making it possible to toggle the output back without restarting
ncmpcpp.

mopidy/core/listener.py

@@ -143,6 +143,17 @@ class CoreListener(object):
         """
         pass
 
+    def mute_changed(self, mute):
+        """
+        Called whenever the mute state is changed.
+
+        *MAY* be implemented by actor.
+
+        :param mute: the new mute state
+        :type mute: boolean
+        """
+        pass
+
     def seeked(self, time_position):
         """
         Called whenever the time position changes by an unexpected amount, e.g.

mopidy/core/playback.py

@@ -304,6 +304,8 @@ class PlaybackController(object):
             # For testing
             self._mute = value
 
+        self._trigger_mute_changed(value)
+
     mute = property(get_mute, set_mute)
     """Mute state as a :class:`True` if muted, :class:`False` otherwise"""
 
@@ -537,6 +539,10 @@ class PlaybackController(object):
         logger.debug('Triggering volume changed event')
         listener.CoreListener.send('volume_changed', volume=volume)
 
+    def _trigger_mute_changed(self, mute):
+        logger.debug('Triggering mute changed event')
+        listener.CoreListener.send('mute_changed', mute=mute)
+
     def _trigger_seeked(self, time_position):
         logger.debug('Triggering seeked event')
         listener.CoreListener.send('seeked', time_position=time_position)

mopidy/frontends/mpd/actor.py

@@ -55,3 +55,6 @@ class MpdFrontend(pykka.ThreadingActor, CoreListener):
 
     def volume_changed(self, volume):
         self.send_idle('mixer')
+
+    def mute_changed(self, mute):
+        self.send_idle('output')

tests/core/listener_test.py

@@ -51,5 +51,8 @@ class CoreListenerTest(unittest.TestCase):
     def test_listener_has_default_impl_for_volume_changed(self):
         self.listener.volume_changed(70)
 
+    def test_listener_has_default_impl_for_mute_changed(self):
+        self.listener.mute_changed(True)
+
     def test_listener_has_default_impl_for_seeked(self):
         self.listener.seeked(0)