Implement removing of rating

__init__.py

@@ -64,6 +64,7 @@ def setup_plugin():
 
 
 hooks = {
-    'setup': setup_plugin,
     'add_media_to_collection': ratings.media_added_to_collection,
+    'remove_media_from_collection': ratings.media_removed_from_collection,
+    'setup': setup_plugin,
     }

ratings.py

@@ -14,20 +14,48 @@
 from .metadata import Metadata
 
 
-def media_added_to_collection(collection, media_entry, note):
+def collection_to_rating(collection):
     m = re.match(r'rating:(\d+)', collection.title)
     if not m:
         return
-    rating_number = int(m.group(1))
-    set_rating_from_media_entry(media_entry, rating_number)
+    try:
+        return int(m.group(1))
+    except ValueError:
+        return
+
+
+def media_added_to_collection(collection, media_entry, note):
+    rating = collection_to_rating(collection)
+    if rating is None:
+        return
+    set_rating_from_media_entry(media_entry, rating)
+
+
+def media_removed_from_collection(collection, media_entry):
+    removed_rating = collection_to_rating(collection)
+    if removed_rating is None:
+        return
+    for col in media_entry.collections:
+        fallback_rating = collection_to_rating(col)
+        if fallback_rating is not None:
+            set_rating_from_media_entry(media_entry, fallback_rating,
+                                        expect_rating=removed_rating)
+            return
+    set_rating_from_media_entry(media_entry, 0,
+                                expect_rating=removed_rating)
 
 
-def set_rating_from_media_entry(media_entry, rating):
+def set_rating_from_media_entry(media_entry, rating, expect_rating=None):
     filepath = (mgg.public_store
                 ._cachefile_to_original_filepath(
                     media_entry.media_files['original']))
     path = mgg.public_store._resolve_filepath(filepath)
-    set_rating(path)
+    if expect_rating is not None:
+        actual_rating = get_rating(path)
+        if actual_rating != expect_rating:
+            return False
+    set_rating(path, rating)
+    return True
 
 
 def set_rating(path, rating):