rind: Respond to the playbin's about-to-finish signal

We use this to load the next track without changing the pipeline state,
which should give us smoother audio switching.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

rind/gst.py

@@ -31,8 +31,14 @@ class EmmentalAudio:
         NextButton.connect( "clicked", self.next)
         ProgScale.connect("change-value", self.seek)
 
+        self.playbin.connect("about-to-finish", self.about_to_finish)
         self.timeout = GLib.timeout_add(100, self.update_progress)
 
+    def about_to_finish(self, playbin):
+        track = curds.PlaylistManager.next()
+        if track:
+            self.playbin.set_property("uri", f"file://{track.path}")
+
     def duration(self):
         (res, cur) = self.playbin.query_duration(Gst.Format.TIME)
         return cur / Gst.SECOND if res == True else 0.0
@@ -44,9 +50,7 @@ class EmmentalAudio:
             self.playbin.set_state(Gst.State.PLAYING)
 
     def next(self, *args):
-        track = curds.PlaylistManager.next()
-        if track != None:
-            self.load(track)
+        self.load(curds.PlaylistManager.next())
 
     def on_message(self, bus, message):
         if message.type == Gst.MessageType.STATE_CHANGED:

rind/test_gst.py

@@ -139,3 +139,9 @@ class TestGst(unittest.TestCase):
             self.main_loop()
         self.assertTrue( gst.PauseButton.is_visible())
         self.assertFalse(gst.PlayButton.is_visible())
+
+        track = curds.PlaylistManager.track
+        self.audio.seek(value=99)
+        time.sleep(0.1)
+        self.main_loop()
+        self.assertNotEqual(curds.PlaylistManager.track, track)