[gnome-music/wip/mschraal/core-gapless: 40/40] player: Fix gapless playback after core rework

[Marinus Schraal <mschraal src gnome org>]

commit 546ffe00d26e48b7f65117de358286222dd427c8
Author: Marinus Schraal <mschraal gnome org>
Date:   Thu Aug 8 12:53:54 2019 +0200

    player: Fix gapless playback after core rework
    
    After the core rewrite, the gapless playback had a minor regression.
    
    Gapless works by preloading the next song when a song is about to
    finish. Getting the next song involves calling 'next' on PlayerPlaylist,
    which also sets the State enum. This enum is since the core rewrite used
    to trigger all UI updates. This resulted in the UI advancing before the
    previous song was actually finished.
    
    This commit restores the sync between the UI and the PlayerPlaylist by
    adding a get_next call, which only retrieves the next song without
    changing the CoreSong state. next is only called when the next song
    actually starts playing. This is achieved by listening to the playbin
    stream-start signal.

 gnomemusic/player.py | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)
---
diff --git a/gnomemusic/player.py b/gnomemusic/player.py
index 2dc2e127..e64044dd 100644
--- a/gnomemusic/player.py
+++ b/gnomemusic/player.py
@@ -126,6 +126,25 @@ class PlayerPlaylist(GObject.GObject):
 
         return False
 
+    def get_next(self):
+        """Get the next song in the playlist.
+
+        :return: The next CoreSong or None.
+        :rtype: CoreSong
+        """
+        if not self.has_next():
+            return None
+
+        if self.props.repeat_mode == RepeatMode.SONG:
+            next_position = self.props.position
+        elif (self.props.repeat_mode == RepeatMode.ALL
+                and self.props.position == self._model.get_n_items() - 1):
+            next_position = 0
+        else:
+            next_position = self.props.position + 1
+
+        return self._model[next_position]
+
     @log
     def next(self):
         """Go to the next song in the playlist.
@@ -440,19 +459,20 @@ class Player(GObject.GObject):
     @log
     def _on_about_to_finish(self, klass):
         if self.props.has_next:
-            self._playlist.next()
-
-            new_url = self._playlist.props.current_song.props.url
+            next_coresong = self._playlist.get_next()
+            new_url = next_coresong.props.url
             self._gst_player.props.url = new_url
             self._gapless_set = True
 
     @log
     def _on_eos(self, klass):
+        self._playlist.next()
+
         if self._gapless_set:
             # After 'eos' in the gapless case, the pipeline needs to be
             # hard reset.
             self.stop()
-            self.play()
+            self.play(self.props.current_song)
         else:
             self.stop()
 
@@ -469,6 +489,9 @@ class Player(GObject.GObject):
             self.next()
 
     def _on_stream_start(self, klass):
+        if self._gapless_set:
+            self._playlist.next()
+
         self._gapless_set = False
         self._time_stamp = int(time.time())