Prepare for gapless play.

- change communication between player and spirc to use player events channel.
- enhance player events channel
- have spirc send loading messages to Spotify
- enable preloading of tracks in the player

examples/play.rs

@@ -7,8 +7,53 @@ use librespot::core::session::Session;
 use librespot::core::spotify_id::SpotifyId;
 use librespot::playback::config::PlayerConfig;
 
+use futures::stream::Stream;
+use futures::{Async, Future, Poll};
 use librespot::playback::audio_backend;
-use librespot::playback::player::Player;
+use librespot::playback::player::{Player, PlayerEvent, PlayerEventChannel};
+
+pub struct SingleTrackPlayer {
+    play_request_id: u64,
+    event_channel: PlayerEventChannel,
+}
+
+impl SingleTrackPlayer {
+    pub fn new(ref mut player: Player, track_id: SpotifyId) -> SingleTrackPlayer {
+        let event_channel = player.get_player_event_channel();
+        let play_request_id = player.load(track_id, true, 0);
+        SingleTrackPlayer {
+            play_request_id,
+            event_channel,
+        }
+    }
+}
+
+impl Future for SingleTrackPlayer {
+    type Item = ();
+    type Error = ();
+
+    fn poll(&mut self) -> Poll<(), ()> {
+        loop {
+            match self.event_channel.poll().unwrap() {
+                Async::NotReady => return Ok(Async::NotReady),
+                Async::Ready(None) => return Ok(Async::Ready(())),
+                Async::Ready(Some(event)) => match event {
+                    PlayerEvent::EndOfTrack {
+                        play_request_id, ..
+                    }
+                    | PlayerEvent::Stopped {
+                        play_request_id, ..
+                    } => {
+                        if play_request_id == self.play_request_id {
+                            return Ok(Async::Ready(()));
+                        }
+                    }
+                    _ => (),
+                },
+            }
+        }
+    }
+}
 
 fn main() {
     let mut core = Core::new().unwrap();
@@ -39,7 +84,7 @@ fn main() {
     });
 
     println!("Playing...");
-    core.run(player.load(track, true, 0)).unwrap();
+    core.run(SingleTrackPlayer::new(player, track)).unwrap();
 
     println!("Done");
 }