[gnome-music/wip/mschraal/insanely-slow-startup-fix-41-backport: 2/3] Add GriloArtQueue

[Marinus Schraal <mschraal src gnome org>]

commit c4d6e9163c122b3141932aabcb40e180a6959fe1
Author: Marinus Schraal <mschraal gnome org>
Date:   Tue Feb 15 10:00:44 2022 +0100

    Add GriloArtQueue
    
    A queue class for Grilo art lookups, which are quite heavily taxing the
    system and are better serialized.

 gnomemusic/griloartqueue.py | 103 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
---
diff --git a/gnomemusic/griloartqueue.py b/gnomemusic/griloartqueue.py
new file mode 100644
index 000000000..b406217c1
--- /dev/null
+++ b/gnomemusic/griloartqueue.py
@@ -0,0 +1,103 @@
+# Copyright 2022 The GNOME Music developers
+#
+# GNOME Music is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# GNOME Music is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with GNOME Music; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+# The GNOME Music authors hereby grant permission for non-GPL compatible
+# GStreamer plugins to be used and distributed together with GStreamer
+# and GNOME Music.  This permission is above and beyond the permissions
+# granted by the GPL license by which GNOME Music is covered.  If you
+# modify this code, you may extend this exception to your version of the
+# code, but you are not obligated to do so.  If you do not wish to do so,
+# delete this exception statement from your version.
+
+from __future__ import annotations
+from typing import Callable, Dict, List, Optional, Union
+import typing
+
+from gi.repository import GLib, GObject
+
+from gnomemusic.storeart import StoreArt
+from gnomemusic.utils import CoreObjectType
+if typing.TYPE_CHECKING:
+    from gnomemusic.application import Application
+    from gnomemusic.corealbum import CoreAlbum
+    from gnomemusic.coreartist import CoreArtist
+    from gnomemusic.coresong import CoreSong
+    CoreObject = Union[CoreAlbum, CoreArtist, CoreSong]
+
+
+class GriloArtQueue(GObject.GObject):
+    """Queue for Grilo art lookup
+
+    Grilo remote art lookup is quite taxing when done in parallel. This
+    class runs the lookup queries serialized.
+    """
+
+    __gtype_name__ = "GriloArtQueue"
+
+    _queue: Dict[CoreObject, CoreObjectType] = {}
+    _active_queue: List[CoreObject] = []
+
+    def __init__(self, application: Application) -> None:
+        """Initialize GriloArtQueue
+
+        :param Application application: The application instance
+        """
+        super().__init__()
+
+        self._coregrilo = application.props.coregrilo
+
+        self._timeout_id = 0
+
+    def queue(
+            self, coreobject: CoreObject,
+            coreobjecttype: CoreObjectType) -> None:
+        """Queue Grilo art lookup for the coreobject
+
+        :param coreobject: Core object to retrieve art for
+        :param CoreObjectType coreobjecttype: The CoreObjectType
+        """
+        if coreobject not in [self._queue.keys(), self._active_queue]:
+            self._queue[coreobject] = coreobjecttype
+
+        if self._timeout_id == 0:
+            self._timeout_id = GLib.timeout_add(100, self._dispatch)
+
+    def _dispatch(self) -> bool:
+        if len(self._queue) == 0:
+            self._timeout_id = 0
+            return GLib.SOURCE_REMOVE
+
+        if len(self._active_queue) > 0:
+            return GLib.SOURCE_CONTINUE
+
+        coreobject, coreobjecttype = self._queue.popitem()
+
+        storeart = StoreArt()
+        storeart.connect("finished", self._on_async_finished, coreobject)
+        if coreobjecttype == CoreObjectType.ARTIST:
+            self._coregrilo.get_artist_art(coreobject, storeart)
+        elif coreobjecttype == CoreObjectType.ALBUM:
+            self._coregrilo.get_album_art(coreobject, storeart)
+        elif coreobjecttype == CoreObjectType.SONG:
+            self._coregrilo.get_song_art(coreobject, storeart)
+
+        self._active_queue.append(coreobject)
+
+        return GLib.SOURCE_CONTINUE
+
+    def _on_async_finished(
+            self, storeart: StoreArt, coreobject: CoreObject) -> None:
+        self._active_queue.remove(coreobject)