PICARD-1339: Remove O(n^2) complexity when deleting files

This change basically makes sure calls to update_metadata_images are done only once per cluster / track when multiple files get removed. Since update_metadata_images iterates over all files inside a cluster doing this after deletion reduces the complexity significantly.

picard/cluster.py

@@ -114,6 +114,8 @@ class Cluster(QtCore.QObject, Item):
         self.item.remove_file(file)
         if not self.special and self.get_num_files() == 0:
             self.tagger.remove_cluster(self)
+
+    def finalize_remove_files(self):
         self.update_metadata_images()
         self._update_related_album()
 

picard/tagger.py

@@ -603,12 +603,17 @@ class Tagger(QtWidgets.QApplication):
 
     def remove_files(self, files, from_parent=True):
         """Remove files from the tagger."""
+        parents = set()
         for file in files:
             if file.filename in self.files:
                 file.clear_lookup_task()
                 self._acoustid.stop_analyze(file)
                 del self.files[file.filename]
                 file.remove(from_parent)
+                parents.add(file.parent)
+        if from_parent:
+            for parent in parents:
+                parent.finalize_remove_files()
 
     def remove_album(self, album):
         """Remove the specified album."""

picard/track.py

@@ -100,6 +100,8 @@ class Track(DataObject, Item):
         file.copy_metadata(file.orig_metadata, preserve_deleted=False)
         self.album._remove_file(self, file)
         file.metadata_images_changed.disconnect(self.update_orig_metadata_images)
+
+    def finalize_remove_files(self):
         self.update()
 
     def update(self):