hopefully streamline playbin state machine

src/playbin.vala

@@ -1,7 +1,13 @@
+enum PlaybinState {
+    STOPPED,
+    PAUSED,
+    PLAYING,
+}
+
 class Playbin : Object {
     // dynamic: undocumented vala feature
     // lets us access the about-to-finish signal
-    private dynamic Gst.Element playbin;
+    private dynamic Gst.Element playbin = Gst.ElementFactory.make ("playbin3", null);
 
     // used to prevent stale seeks
     private uint64 stream_counter = 0;
@@ -21,21 +27,25 @@ class Playbin : Object {
         set { this.playbin.mute = value; }
     }
 
+    public PlaybinState state { get; private set; default = PlaybinState.STOPPED; }
+
     private bool seeking = false;
     public int64 position { get; private set; }
     public int64 duration { get; private set; }
 
-    public signal void stream_started (string uri);
+    private bool notify_next_transition;
-    public signal void stream_over ();
+
+    // public void begin_playback (string uri);
+    // public void prepare_next (string? next_uri);
+    public signal void song_transition (string uri);
+    public signal void playback_finished ();
+    // public void stop_playback ();
 
     private void source_setup (Gst.Element playbin, dynamic Gst.Element source) {
         source.user_agent = "audrey/linux";
     }
 
     construct {
-        this.playbin = Gst.ElementFactory.make ("playbin3", null);
-        assert (this.playbin != null);
-
         this.playbin.source_setup.connect (this.source_setup);
         this.playbin.about_to_finish.connect (this.about_to_finish);
 
@@ -78,24 +88,13 @@ class Playbin : Object {
             Gst.State new_state;
             message.parse_state_changed (out old_state, out new_state, null);
 
-            switch (new_state) {
+            if (new_state == Gst.State.PLAYING) {
-            case Gst.State.NULL:
-                break;
-
-            case Gst.State.READY:
-                break;
-
-            case Gst.State.PAUSED:
-                break;
-
-            case Gst.State.PLAYING:
                 if (this.queued_seek_position < 0) {
                     this.seeking = false;
                 } else if (this.queued_seek_counter == this.stream_counter) {
                     assert (this.playbin.seek_simple (Gst.Format.TIME, Gst.SeekFlags.FLUSH, this.queued_seek_position));
                 }
                 this.queued_seek_position = -1;
-                break;
             }
         });
 
@@ -106,11 +105,16 @@ class Playbin : Object {
             assert (this.playbin.query_duration (Gst.Format.TIME, out new_duration));
             this.duration = new_duration;
 
-            this.stream_started ((string) this.playbin.current_uri);
+            if (notify_next_transition) {
+                this.song_transition ((string) this.playbin.current_uri);
+            } else {
+                notify_next_transition = true;
+            }
         });
         
         bus.message["eos"].connect ((message) => {
-            this.stream_over ();
+            assert (notify_next_transition);
+            this.playback_finished ();
         });
     }
 
@@ -118,7 +122,9 @@ class Playbin : Object {
     private int64 queued_seek_position = -1;
 
     public void seek (int64 position) {
-        if (this.playbin.seek_simple (Gst.Format.TIME, Gst.SeekFlags.FLUSH/* | Gst.SeekFlags.KEY_UNIT*/, position)) {
+        if (this.state == PlaybinState.STOPPED) return;
+
+        if (this.playbin.seek_simple (Gst.Format.TIME, Gst.SeekFlags.FLUSH, position)) {
             this.seeking = true;
             this.position = position;
         } else {
@@ -128,18 +134,19 @@ class Playbin : Object {
         }
     }
 
-    public void play_now (string uri) {
+    public void begin_playback (string uri) {
         this.playbin.set_state (Gst.State.READY);
         this.playbin.uri = uri;
         this.playbin.set_state (Gst.State.PLAYING);
 
-        this.set_next_uri (uri);
+        this.state = PlaybinState.PLAYING;
+        this.notify_next_transition = false;
     }
 
     Mutex next_uri_lock;
     string? next_uri;
 
-    public void set_next_uri (string? next_uri) {
+    public void prepare_next (string? next_uri) {
         this.next_uri_lock.lock ();
         this.next_uri = next_uri;
         this.next_uri_lock.unlock ();
@@ -158,10 +165,19 @@ class Playbin : Object {
     }
 
     public void pause () {
+        assert (this.state != PlaybinState.STOPPED);
         this.playbin.set_state (Gst.State.PAUSED);
+        this.state = PlaybinState.PAUSED;
     }
 
     public void play () {
+        assert (this.state != PlaybinState.STOPPED);
         this.playbin.set_state (Gst.State.PLAYING);
+        this.state = PlaybinState.PLAYING;
+    }
+
+    public void stop_playback() {
+        this.playbin.set_state (Gst.State.READY);
+        this.state = PlaybinState.STOPPED;
     }
 }

src/ui/play_queue.vala

@@ -2,14 +2,10 @@ class Ui.PlayQueueStore : Object, ListModel, Gtk.SelectionModel {
     public ListStore inner = new ListStore (typeof (Song));
     public uint playing_index { get; private set; default = 0; }
 
-    private bool starting_stream = false;
+    public signal void begin_playback (Song song);
-
+    public signal void prepare_next (Song? song);
-    public signal void stop_stream ();
+    public signal void playback_continues (Song song);
-    public signal void start_stream (Song song);
+    public signal void stop_playback ();
-    // public void on_song_start ();
-    public signal void now_playing (Song song);
-    public signal void prepare_next_song (Song? song);
-    // public void on_stream_end ();
 
     construct {
         this.inner.items_changed.connect ((position, removed, added) => {
@@ -17,18 +13,17 @@ class Ui.PlayQueueStore : Object, ListModel, Gtk.SelectionModel {
                 if (this.playing_index < position+removed) {
                     this.playing_index = position;
                     if (this.playing_index < this.inner.get_n_items ()) {
-                        this.starting_stream = true;
+                        this.begin_playback ((Song) this.inner.get_item (this.playing_index));
-                        this.now_playing ((Song) this.inner.get_item (this.playing_index));
+                        this.prepare_next ((Song?) this.inner.get_item (this.playing_index+1));
-                        this.start_stream((Song) this.inner.get_item (this.playing_index));
                     } else {
-                        this.stop_stream ();
+                        this.stop_playback ();
                     }
                 } else {
                     this.playing_index += added;
                     this.playing_index -= removed;
                 }
             } else {
-                this.prepare_next_song ((Song?) this.inner.get_item (this.playing_index+1));
+                this.prepare_next ((Song?) this.inner.get_item (this.playing_index+1));
             }
 
             this.items_changed (position, removed, added);
@@ -38,15 +33,17 @@ class Ui.PlayQueueStore : Object, ListModel, Gtk.SelectionModel {
         });
     }
 
-    public void on_stream_start () {
+    public void song_transition () {
-        if (!starting_stream) {
+        this.playing_index += 1;
-            this.playing_index += 1;
+        this.selection_changed (this.playing_index-1, 2);
-            this.selection_changed (this.playing_index-1, 2);
+        this.playback_continues ((Song) this.inner.get_item (this.playing_index));
-            this.now_playing ((Song) this.inner.get_item (this.playing_index));
+        this.prepare_next ((Song?) this.inner.get_item (this.playing_index+1));
-        }
+    }
 
-        this.prepare_next_song ((Song?) this.inner.get_item (this.playing_index+1));
+    public void playback_finished () {
-        starting_stream = false;
+        this.playing_index += 1;
+        assert (this.playing_index == this.inner.get_n_items ());
+        this.selection_changed (this.playing_index-1, 1);
     }
 
     Gtk.Bitset get_selection_in_range (uint position, uint n_items) {
@@ -78,9 +75,8 @@ class Ui.PlayQueueStore : Object, ListModel, Gtk.SelectionModel {
         }
         this.selection_changed (position, 1);
 
-        this.starting_stream = true;
+        this.begin_playback ((Song) this.inner.get_item (this.playing_index));
-        this.now_playing ((Song) this.inner.get_item (this.playing_index));
+        this.prepare_next ((Song) this.inner.get_item (this.playing_index+1));
-        this.start_stream ((Song) this.inner.get_item (this.playing_index));
 
         return true;
     }
@@ -123,9 +119,10 @@ public class Ui.PlayQueue : Adw.NavigationPage {
     [GtkChild] private unowned Gtk.ColumnView view;
     PlayQueueStore store = new PlayQueueStore ();
 
-    public signal void play_now (Song song);
+    public signal void begin_playback (Song song);
-    public signal void play_next (Song? song);
+    public signal void prepare_next (Song? next_song);
-    public signal void now_playing (Song song);
+    public signal void playback_continues (Song song);
+    public signal void stop_playback ();
 
     public bool can_clear_all { get; private set; default = false; }
 
@@ -137,17 +134,22 @@ public class Ui.PlayQueue : Adw.NavigationPage {
         this.store.inner.remove_all ();
         this.can_clear_all = false;
 
-        this.store.start_stream.connect ((song) => this.play_now(song));
+        this.store.begin_playback.connect ((song) => this.begin_playback (song));
-        this.store.now_playing.connect ((song) => this.now_playing(song));
+        this.store.prepare_next.connect ((next_song) => this.prepare_next (next_song));
-        this.store.prepare_next_song.connect ((song) => this.play_next(song));
+        this.store.playback_continues.connect ((song) => this.playback_continues (song));
+        this.store.stop_playback.connect (() => this.stop_playback ());
     }
 
     public void queue (Song song) {
         this.store.inner.append (song);
     }
 
-    internal void on_stream_start () {
+    internal void song_transition () {
-        this.store.on_stream_start ();
+        this.store.song_transition ();
+    }
+
+    internal void playback_finished () {
+        this.store.playback_finished ();
     }
 
     internal void restart () {

src/ui/window.blp

@@ -69,7 +69,7 @@ template $UiWindow: Adw.ApplicationWindow {
             }
 
             Picture {
-paintable: bind template.playing_cover_art;
+              paintable: bind template.playing_cover_art;
             }
           };
         }
@@ -164,6 +164,7 @@ paintable: bind template.playing_cover_art;
           Button {
             icon-name: "media-skip-backward";
             valign: center;
+            sensitive: bind $playbin_active (template.playbin as <$Playbin>.state as <$PlaybinState>) as <bool>;
 
             clicked => $on_skip_backward_clicked ();
           }
@@ -171,13 +172,15 @@ paintable: bind template.playing_cover_art;
           Button {
             icon-name: "media-seek-backward";
             valign: center;
+            sensitive: bind $playbin_active (template.playbin as <$Playbin>.state as <$PlaybinState>) as <bool>;
 
             clicked => $seek_backward ();
           }
 
           Button {
-            icon-name: bind $play_button_icon_name (template.playing) as <string>;
+            icon-name: bind $play_pause_icon_name (template.playbin as <$Playbin>.state as <$PlaybinState>) as <string>;
             valign: center;
+            sensitive: bind $playbin_active (template.playbin as <$Playbin>.state as <$PlaybinState>) as <bool>;
 
             clicked => $on_play_pause_clicked ();
           }
@@ -185,6 +188,7 @@ paintable: bind template.playing_cover_art;
           Button {
             icon-name: "media-seek-forward";
             valign: center;
+            sensitive: bind $playbin_active (template.playbin as <$Playbin>.state as <$PlaybinState>) as <bool>;
 
             clicked => $seek_forward ();
           }
@@ -192,6 +196,7 @@ paintable: bind template.playing_cover_art;
           Button {
             icon-name: "media-skip-forward";
             valign: center;
+            sensitive: bind $playbin_active (template.playbin as <$Playbin>.state as <$PlaybinState>) as <bool>;
 
             clicked => $on_skip_forward_clicked ();
           }

src/ui/window.vala

@@ -8,8 +8,6 @@ class Ui.Window : Adw.ApplicationWindow {
     [GtkChild] public unowned Adw.ButtonRow shuffle_all_tracks;
 
     private Setup setup;
-
-    public bool playing { get; private set; default = false; }
     
     public int64 position { get; private set; }
 
@@ -82,23 +80,36 @@ class Ui.Window : Adw.ApplicationWindow {
                 });
             });
 
-            playbin.stream_started.connect (this.play_queue.on_stream_start);
+            this.play_queue.begin_playback.connect ((song) => {
+                var uri = api.stream_uri (song.id);
+                this.playbin.begin_playback (uri);
 
-            this.play_queue.now_playing.connect ((song) => {
-                this.playing = true;
                 this.song = song;
                 api.scrobble.begin (song.id);
             });
 
-            this.play_queue.play_now.connect ((song) => {
+            this.play_queue.prepare_next.connect ((next_song) => {
-                playbin.play_now (api.stream_uri (song.id));
+                var next_uri = next_song == null ? null : api.stream_uri (next_song.id);
+                this.playbin.prepare_next (next_uri);
             });
-            this.play_queue.play_next.connect ((song) => {
+
-                if (song == null) {
+            this.playbin.song_transition.connect ((uri) => {
-                    playbin.set_next_uri (null);
+                this.play_queue.song_transition ();
-                } else {
+            });
-                    playbin.set_next_uri (api.stream_uri (song.id));
+
-                }
+            this.play_queue.playback_continues.connect ((song) => {
+                this.song = song;
+                api.scrobble.begin (song.id);
+            });
+
+            this.playbin.playback_finished.connect (() => {
+                this.play_queue.playback_finished ();
+                this.song = null;
+            });
+
+            this.play_queue.stop_playback.connect (() => {
+                this.playbin.stop_playback ();
+                this.song = null;
             });
         });
         this.setup.load ();
@@ -166,17 +177,23 @@ class Ui.Window : Adw.ApplicationWindow {
     }
 
     [GtkCallback] private void on_play_pause_clicked () {
-        if (this.playing) {
+        if (this.playbin.state == PlaybinState.PLAYING) {
             this.playbin.pause();
-            this.playing = false;
         } else {
             this.playbin.play();
-            this.playing = true;
         }
     }
 
-    [GtkCallback] private string play_button_icon_name (bool playing) {
+    [GtkCallback] private string play_pause_icon_name (PlaybinState state) {
-        return playing ? "media-playback-pause" : "media-playback-start";
+        if (state == PlaybinState.PLAYING) {
+            return "media-playback-pause";
+        } else {
+            return "media-playback-start";
+        }
+    }
+
+    [GtkCallback] private bool playbin_active (PlaybinState state) {
+        return state != PlaybinState.STOPPED;
     }
 
     [GtkCallback] private string mute_button_icon_name (bool mute) {