Refactor and Clean-up Viewsets

- Reorder the code inside the methods to fail fast on autorization,
- Replace `int_or_none` with a more generic solution, and move to utils,
- Add `get_values` and move `pk_and_slug` as `get_pk_and_slug` into utils,
- Replace calls to static methos in models local queries,
- Return meaningful status code while creating and updating resources,
- Return `409` when creating or updating a schedule produces a conflict.

program/utils.py

@@ -19,6 +19,7 @@
 #
 
 from datetime import datetime, date, time
+from typing import Dict, Optional, Union, Tuple
 
 import requests
 from django.utils import timezone
@@ -73,3 +74,30 @@ def get_audio_url(cba_id):
         audio_url = requests.get(url).json()
 
     return audio_url
+
+
+def get_values(kwargs: Dict[str, str], *keys: str) -> Union[Tuple[Union[int, str, None], ...], int, str, None]:
+    """Get the values of the keys from the kwargs."""
+
+    def int_if_digit(value: Optional[str]) -> Optional[Union[int, str]]:
+        return int(value) if value and value.isdigit() else value
+
+    values = [kwargs.get(key) for key in keys]
+
+    if len(values) > 1:
+        return tuple(int_if_digit(value) for value in values)
+    else:
+        return int_if_digit(values[0])
+
+
+def get_pk_and_slug(kwargs: Dict[str, str]) -> Tuple[Optional[int], Optional[str]]:
+    """Get the pk and the slug from the kwargs."""
+
+    pk, slug = None, None
+
+    try:
+        pk = int(kwargs['pk'])
+    except ValueError:
+        slug = kwargs['pk']
+
+    return pk, slug