Resolve "Check permission rules if they handle lessons with substitutions correctly"

Closes #147 (closed)

get_teachers will return the following:

• simply the teachers for events and extra lessons
• the original teachers for lesson periods without substitution, otherwise the new teacher

So, we have to check the teachers of lesson periods additionally to keep the access for the original teacher.

aleksis/apps/alsijil/util/predicates.py

@@ -22,8 +22,22 @@ def is_none(user: User, obj: Any) -> bool:
 def is_lesson_teacher(user: User, obj: Union[LessonPeriod, Event, ExtraLesson]) -> bool:
     """Predicate for teachers of a lesson.
 
-    Checks whether the person linked to the user is a teacher
-    in the lesson or the substitution linked to the given LessonPeriod.
+    Checks whether the person linked to the user is a teacher in the register object.
+    If the register object is a lesson period and has a substitution linked,
+    this will **only** check if the person is one of the substitution teachers.
+    """
+    if obj:
+        return user.person in obj.get_teachers().all()
+    return False
+
+
+@predicate
+def is_lesson_original_teacher(user: User, obj: Union[LessonPeriod, Event, ExtraLesson]) -> bool:
+    """Predicate for teachers of a lesson.
+
+    Checks whether the person linked to the user is a teacher in the register object.
+    If the register object is a lesson period and has a substitution linked,
+    this will **also** check if the person is one of the substitution teachers.
     """
     if obj:
         if isinstance(obj, LessonPeriod) and user.person in obj.lesson.teachers.all():
@@ -205,10 +219,26 @@ def is_own_personal_note(user: User, obj: PersonalNote) -> bool:
 
 @predicate
 def is_personal_note_lesson_teacher(user: User, obj: PersonalNote) -> bool:
-    """Predicate for teachers of a lesson referred to in the lesson period of a personal note.
+    """Predicate for teachers of a register object linked to a personal note.
+
+    Checks whether the person linked to the user is a teacher
+    in the register object linked to the personal note.
+    If the register object is a lesson period and has a substitution linked,
+    this will **only** check if the person is one of the substitution teachers.
+    """
+    if hasattr(obj, "register_object"):
+        return user.person in obj.register_object.get_teachers().all()
+    return False
+
+
+@predicate
+def is_personal_note_lesson_original_teacher(user: User, obj: PersonalNote) -> bool:
+    """Predicate for teachers of a register object linked to a personal note.
 
     Checks whether the person linked to the user is a teacher
-    in the lesson or the substitution linked to the LessonPeriod of the given PersonalNote.
+    in the register object linked to the personal note.
+    If the register object is a lesson period and has a substitution linked,
+    this will **also** check if the person is one of the substitution teachers.
     """
     if hasattr(obj, "register_object"):
         if (