[gnome-settings-daemon] media-keys: Use heuristic to switch MPRIS clients

[Benjamin Berg <bberg src gnome org>]

commit ae95b871d2ea4409a95c750d8ce63c9e5b29a6b8
Author: Ryan Hendrickson <ryan hendrickson alum mit edu>
Date:   Sat Jun 27 19:12:13 2020 -0400

    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 | 174 +++++++++++++++++++++-------------
 1 file changed, 106 insertions(+), 68 deletions(-)
---
diff --git a/plugins/media-keys/mpris-controller.c b/plugins/media-keys/mpris-controller.c
index a1d19e30..80d10051 100644
--- a/plugins/media-keys/mpris-controller.c
+++ b/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);
 }