From 353cf22dfb16dd55e618fe9df998b4c7bbde2649 Mon Sep 17 00:00:00 2001
From: Hellow <Lars.Noack@outlook.de>
Date: Mon, 13 Feb 2023 16:45:12 +0100
Subject: [PATCH] Update object_cache.py

clean code
---
 src/music_kraken/database/object_cache.py | 88 +++++++++++++++++------
 1 file changed, 67 insertions(+), 21 deletions(-)

diff --git a/src/music_kraken/database/object_cache.py b/src/music_kraken/database/object_cache.py
index 382a364..b82fb25 100644
--- a/src/music_kraken/database/object_cache.py
+++ b/src/music_kraken/database/object_cache.py
@@ -1,4 +1,6 @@
-from typing import Dict, List
+from collections import defaultdict
+from typing import Dict, List, Optional
+import weakref
 
 from .objects import MusicObject
 
@@ -9,52 +11,96 @@ This is necessary, to not have duplicate objects with the same id.
 Using a cache that maps the ojects to their id has multiple benefits:
  - if you modify the object at any point, all objects with the same id get modified *(copy by reference)*
  - less ram usage
+ - to further decrease ram usage I only store weak refs and not a strong reference, for the gc to still work
 """
 
+
 class ObjectCache:
     """
-    :attr object_to_id: maps any object from the Database like Song or Artist to its id.
-    """
+    ObjectCache is a cache for the objects retrieved from a database.
+    It maps each object to its id and uses weak references to manage its memory usage.
+    Using a cache for these objects provides several benefits:
+
+    - Modifying an object updates all objects with the same id (due to copy by reference)
+    - Reduced memory usage
+
+    :attr object_to_id: Dictionary that maps MusicObjects to their id.
+    :attr weakref_map: Dictionary that uses weak references to MusicObjects as keys and their id as values.
+
+    :method exists: Check if a MusicObject already exists in the cache.
+    :method append: Add a MusicObject to the cache if it does not already exist.
+    :method extent: Add a list of MusicObjects to the cache.
+    :method remove: Remove a MusicObject from the cache by its id.
+    :method get: Retrieve a MusicObject from the cache by its id.    """
     object_to_id: Dict[str, MusicObject]
+    weakref_map: Dict[weakref.ref, str]
 
     def __init__(self) -> None:
         self.object_to_id = dict()
-    
-
-    def clear(self) -> None:
-        """
-        deletes all references and lets the gc clean up the rest
-        this should free up memorie.
-
-        If not, check if you have any references to an object in you're code.
-        It is likely that this object crossreferences to many objects
-        """
-        self.object_to_id = dict()
+        self.weakref_map = defaultdict()
 
     def exists(self, music_object: MusicObject) -> bool:
         """
-        :returns exist: if an element with the same id exists it returns true, else false
+        Check if a MusicObject with the same id already exists in the cache.
+
+        :param music_object: The MusicObject to check for.
+        :return: True if the MusicObject exists, False otherwise.
         """
         if music_object.dynamic:
             return True
-        if music_object.id in self.object_to_id:
-            return True
-        return False
+        return music_object.id in self.object_to_id
+
+    def on_death(self, weakref_: weakref.ref) -> None:
+        """
+        Callback function that gets triggered when the reference count of a MusicObject drops to 0.
+        This function removes the MusicObject from the cache.
+
+        :param weakref_: The weak reference of the MusicObject that has been garbage collected.
+        """
+        data_id = self.weakref_map.pop(weakref_)
+        self.object_to_id.pop(data_id)
 
     def append(self, music_object: MusicObject) -> bool:
         """
-        :returns exist: if an element with the same id exists it returns true, else false
+        Add a MusicObject to the cache.
+
+        :param music_object: The MusicObject to add to the cache.
+        :return: True if the MusicObject already exists in the cache, False otherwise.
         """
         if self.exists(music_object):
             return True
 
+        self.weakref_map[weakref.ref(music_object, self.on_death)] = music_object.id
         self.object_to_id[music_object.id] = music_object
 
         return False
 
     def extent(self, music_object_list: List[MusicObject]):
         """
-        adjacent to the extend method of list, this appends n Object
+        adjacent to the extent method of list, this appends n Object
         """
         for music_object in music_object_list:
-            self.append(music_object)
\ No newline at end of file
+            self.append(music_object)
+
+    def remove(self, _id: str):
+        """
+        Remove a MusicObject from the cache.
+
+        :param _id: The id of the MusicObject to remove from the cache.
+        """
+        data = self.object_to_id.get(_id)
+        if data:
+            self.weakref_map.pop(weakref.ref(data))
+            self.object_to_id.pop(_id)
+
+    def __getitem__(self, item) -> Optional[MusicObject]:
+        """
+        this returns the data obj
+        :param item: the id of the music object
+        :return:
+        """
+
+        return self.object_to_id.get(item)
+
+    def get(self, _id: str) -> Optional[MusicObject]:
+        return self.__getitem__(_id)