music_kraken/objects/collection.py

@@ -1,16 +1,44 @@
 from __future__ import annotations
 
-from collections import defaultdict
-from typing import TypeVar, Generic, Dict, Optional, Iterable, List, Iterator, Tuple, Generator, Union, Any, Set
 import copy
+from collections import defaultdict
+from dataclasses import dataclass
+from typing import (Any, Callable, Dict, Generator, Generic, Iterable,
+                    Iterator, List, Optional, Set, Tuple, TypeVar, Union)
 
-from .parents import OuterProxy
-from ..utils import object_trace
-from ..utils import output, BColors
+from ..utils import BColors, object_trace, output
+from .parents import InnerData, OuterProxy
 
 T = TypeVar('T', bound=OuterProxy)
 
 
+@dataclass
+class AppendHookArguments:
+    """
+    This class is used to store the arguments for the append hook.
+    The best explanation is with an examples:
+    
+    ```
+    # this is the action that triggers the append hook
+    album = Album()
+    song = Song()
+    album.song_collection.append(song)
+    ```
+
+    In this case, the append hook is triggered with the following arguments:
+    ```
+    AppendHookArguments(
+        collection=album.song_collection,
+        new_object=song,
+        collection_root_objects=[album]
+    )
+    ```
+    """
+
+    collection: Collection
+    new_object: T
+    collection_root_objects: Set[InnerData]
+
 class Collection(Generic[T]):
     __is_collection__ = True
 
@@ -27,6 +55,7 @@ class Collection(Generic[T]):
             sync_on_append: Dict[str, Collection] = None,
             append_object_to_attribute: Dict[str, T] = None,
             extend_object_to_attribute: Dict[str, Collection] = None,
+            append_callbacks: List[Callable[[AppendHookArguments], None]] = None,
     ) -> None:
         self._collection_for: dict = dict()
 
@@ -41,6 +70,7 @@ class Collection(Generic[T]):
         self.sync_on_append: Dict[str, Collection] = sync_on_append or {}
         self.pull_from: List[Collection] = []
         self.push_to: List[Collection] = []
+        self.append_callbacks: List[Callable[[AppendHookArguments], None]] = append_callbacks or []
 
         # This is to cleanly unmap previously mapped items by their id
         self._indexed_from_id: Dict[int, Dict[str, Any]] = defaultdict(dict)
@@ -141,6 +171,14 @@ class Collection(Generic[T]):
         for attribute, new_object in self.append_object_to_attribute.items():
             other.__getattribute__(attribute).append(new_object, **kwargs)
 
+        append_hook_args = AppendHookArguments(
+            collection=self,
+            new_object=other,
+            collection_root_objects=self._collection_for.keys(),
+        )
+        for callback in self.append_callbacks:
+            callback(append_hook_args)
+
     def append(self, other: Optional[T], **kwargs):
         """
         If an object, that represents the same entity exists in a relevant collection,