media-keys: Use heuristic to switch MPRIS clients

Instead of holding on to an MPRIS client for its entire lifetime, switch
to another client when it starts playing or when it first appears on the
bus, but only if the current client is not itself playing.

plugins/media-keys/mpris-controller.c

@@ -32,14 +32,11 @@ struct _MprisController
   GCancellable *cancellable;
   GDBusProxy *mpris_client_proxy;
   guint namespace_watcher_id;
-  GSList *other_players;
-  gboolean connecting;
+  GSList *other_proxies;
 };
 
 G_DEFINE_TYPE (MprisController, mpris_controller, G_TYPE_OBJECT)
 
-static void mpris_player_try_connect (MprisController *self);
-
 static void
 mpris_controller_dispose (GObject *object)
 {
@@ -54,11 +51,7 @@ mpris_controller_dispose (GObject *object)
       self->namespace_watcher_id = 0;
     }
 
-  if (self->other_players)
-    {
-      g_slist_free_full (self->other_players, g_free);
-      self->other_players = NULL;
-    }
+  g_clear_slist (&self->other_proxies, g_object_unref);
 
   G_OBJECT_CLASS (mpris_controller_parent_class)->dispose (object);
 }
@@ -99,22 +92,94 @@ mpris_controller_key (MprisController *self, const gchar *key)
   return TRUE;
 }
 
+static gboolean
+mpris_client_is_playing (GDBusProxy *proxy)
+{
+  g_autoptr(GVariant) playback_status;
+  const gchar *status_str;
+
+  playback_status = g_dbus_proxy_get_cached_property (proxy, "PlaybackStatus");
+  if (!playback_status)
+    return FALSE;
+
+  if (!g_variant_is_of_type (playback_status, G_VARIANT_TYPE_STRING))
+    return FALSE;
+
+  status_str = g_variant_get_string (playback_status, NULL);
+  return g_strcmp0 (status_str, "Playing") == 0;
+}
+
 static void
 mpris_client_notify_name_owner_cb (GDBusProxy      *proxy,
                                    GParamSpec      *pspec,
                                    MprisController *self)
 {
   g_autofree gchar *name_owner = NULL;
+  GSList *first;
 
   /* Owner changed, but the proxy is still valid. */
   name_owner = g_dbus_proxy_get_name_owner (proxy);
   if (name_owner)
     return;
 
-  g_clear_object (&self->mpris_client_proxy);
-  g_object_notify (G_OBJECT (self), "has-active-player");
+  if (proxy == self->mpris_client_proxy)
+    {
+      g_debug ("Clearing the current MPRIS client proxy");
+      g_clear_object (&self->mpris_client_proxy);
+
+      if ((first = self->other_proxies))
+        {
+          self->mpris_client_proxy = first->data;
+          self->other_proxies = first->next;
+          g_slist_free_1 (first);
 
-  mpris_player_try_connect (self);
+          g_debug ("Falling back to MPRIS client %s",
+                   g_dbus_proxy_get_name (self->mpris_client_proxy));
+        }
+      else
+        {
+          g_object_notify (G_OBJECT (self), "has-active-player");
+        }
+    }
+  else
+    {
+      g_debug ("Forgetting MPRIS client %s", g_dbus_proxy_get_name (proxy));
+      self->other_proxies = g_slist_remove (self->other_proxies, proxy);
+      g_object_unref (proxy);
+    }
+}
+
+static void
+mpris_client_properties_changed_cb (GDBusProxy *proxy,
+                                    GVariant   *changed_properties,
+                                    GStrv       invalidated_properties,
+                                    gpointer    user_data)
+{
+  MprisController *self = MPRIS_CONTROLLER (user_data);
+  GDBusProxy *current_proxy;
+
+  current_proxy = self->mpris_client_proxy;
+  if (current_proxy == proxy)
+    return;
+
+  if (current_proxy && mpris_client_is_playing (current_proxy))
+    return;
+
+  if (mpris_client_is_playing (proxy))
+    {
+      g_debug ("Switching to MPRIS client %s because it is playing",
+               g_dbus_proxy_get_name (proxy));
+
+      self->other_proxies = g_slist_remove (self->other_proxies, proxy);
+
+      if (current_proxy)
+        self->other_proxies = g_slist_prepend (self->other_proxies, current_proxy);
+
+      self->mpris_client_proxy = proxy;
+
+      if (!current_proxy)
+        g_object_notify (user_data, "has-active-player");
+    }
 }
 
 static void
@@ -125,36 +190,52 @@ mpris_proxy_ready_cb (GObject      *object,
   MprisController *self = MPRIS_CONTROLLER (user_data);
   GError *error = NULL;
   GDBusProxy *proxy;
+  const gchar *name;
 
   proxy = g_dbus_proxy_new_for_bus_finish (res, &error);
 
   if (!proxy)
     {
       if (!g_error_matches (error, G_IO_ERROR, G_IO_ERROR_CANCELLED))
-        {
-          g_warning ("Error connecting to mpris interface %s", error->message);
-
-          self->connecting = FALSE;
-
-          mpris_player_try_connect (MPRIS_CONTROLLER (user_data));
-        }
+        g_warning ("Error connecting to MPRIS interface: %s", error->message);
       g_clear_error (&error);
       return;
     }
 
-  self->mpris_client_proxy = proxy;
-  self->connecting = FALSE;
-
   g_signal_connect (proxy, "notify::g-name-owner",
                     G_CALLBACK (mpris_client_notify_name_owner_cb), user_data);
 
+  g_signal_connect (proxy, "g-properties-changed",
+                    G_CALLBACK (mpris_client_properties_changed_cb), user_data);
+
+  name = g_dbus_proxy_get_name (proxy);
+
+  if (self->mpris_client_proxy)
+    {
+      if (mpris_client_is_playing (self->mpris_client_proxy))
+        {
+          g_debug ("Remembering %s for later because the current MPRIS client is playing",
+                   name);
+          self->other_proxies = g_slist_prepend (self->other_proxies, proxy);
+          return;
+        }
+
+      g_debug ("Remembering the current MPRIS client for later");
+      self->other_proxies =
+        g_slist_prepend (self->other_proxies, self->mpris_client_proxy);
+    }
+
+  g_debug ("Switching to MPRIS client %s because it just appeared", name);
+
+  self->mpris_client_proxy = proxy;
+
   g_object_notify (user_data, "has-active-player");
 }
 
 static void
 start_mpris_proxy (MprisController *self, const gchar *name)
 {
-  g_debug ("Creating proxy for for %s", name);
+  g_debug ("Creating proxy for %s", name);
   g_dbus_proxy_new_for_bus (G_BUS_TYPE_SESSION,
                             0,
                             NULL,
@@ -164,29 +245,6 @@ start_mpris_proxy (MprisController *self, const gchar *name)
                             self->cancellable,
                             mpris_proxy_ready_cb,
                             self);
-  self->connecting = TRUE;
-}
-
-static void
-mpris_player_try_connect (MprisController *self)
-{
-  GSList *first;
-  gchar *name;
-
-  if (self->connecting || self->mpris_client_proxy)
-    return;
-
-  if (!self->other_players)
-    return;
-
-  first = self->other_players;
-  name = first->data;
-
-  start_mpris_proxy (self, name);
-
-  self->other_players = self->other_players->next;
-  g_free (name);
-  g_slist_free_1 (first);
 }
 
 static void
@@ -195,27 +253,7 @@ mpris_player_appeared (GDBusConnection *connection,
                        const gchar     *name_owner,
                        gpointer         user_data)
 {
-  MprisController *self = user_data;
-
-  self->other_players = g_slist_prepend (self->other_players, g_strdup (name));
-  mpris_player_try_connect (self);
-}
-
-static void
-mpris_player_vanished (GDBusConnection *connection,
-                       const gchar     *name,
-                       gpointer         user_data)
-{
-  MprisController *self = user_data;
-  GSList *elem;
-
-  elem = g_slist_find_custom (self->other_players, name, (GCompareFunc) g_strcmp0);
-  if (elem)
-    {
-      self->other_players = g_slist_remove_link (self->other_players, elem);
-      g_free (elem->data);
-      g_slist_free_1 (elem);
-    }
+  start_mpris_proxy (MPRIS_CONTROLLER (user_data), name);
 }
 
 static void
@@ -226,7 +264,7 @@ mpris_controller_constructed (GObject *object)
   self->namespace_watcher_id = bus_watch_namespace (G_BUS_TYPE_SESSION,
                                                     "org.mpris.MediaPlayer2",
                                                     mpris_player_appeared,
-                                                    mpris_player_vanished,
+                                                    NULL,
                                                     MPRIS_CONTROLLER (object),
                                                     NULL);
 }