Resolve "Review permissions"

Closes #83 (closed)

aleksis/apps/chronos/util/chronos_helpers.py

 from typing import Optional
 
+from django.contrib.auth.models import User
+from django.db.models import Count, Q
 from django.http import HttpRequest, HttpResponseNotFound
 from django.shortcuts import get_object_or_404
 
+from guardian.core import ObjectPermissionChecker
+
 from aleksis.core.models import Group, Person
+from aleksis.core.util.predicates import check_global_permission
 
 from ..managers import TimetableType
 from ..models import LessonPeriod, LessonSubstitution, Room
@@ -37,3 +42,82 @@ def get_substitution_by_id(request: HttpRequest, id_: int, week: int):
     return LessonSubstitution.objects.filter(
         week=wanted_week.week, year=wanted_week.year, lesson_period=lesson_period
     ).first()
+
+
+def get_teachers(user: User):
+    checker = ObjectPermissionChecker(user)
+
+    teachers = (
+        Person.objects.annotate(lessons_count=Count("lessons_as_teacher"))
+        .filter(lessons_count__gt=0)
+        .order_by("short_name", "last_name")
+    )
+
+    if not check_global_permission(user, "chronos.view_all_person_timetables"):
+        checker.prefetch_perms(teachers)
+
+        wanted_teachers = set()
+
+        for teacher in teachers:
+            if checker.has_perm("core.view_person_timetable", teacher):
+                wanted_teachers.add(teacher.pk)
+
+        teachers = teachers.filter(Q(pk=user.person.pk) | Q(pk__in=wanted_teachers))
+
+    return teachers
+
+
+def get_classes(user: User):
+    checker = ObjectPermissionChecker(user)
+
+    classes = (
+        Group.objects.for_current_school_term_or_all()
+        .annotate(
+            lessons_count=Count("lessons"), child_lessons_count=Count("child_groups__lessons"),
+        )
+        .filter(
+            Q(lessons_count__gt=0, parent_groups=None)
+            | Q(child_lessons_count__gt=0, parent_groups=None)
+        )
+        .order_by("short_name", "name")
+    )
+
+    if not check_global_permission(user, "chronos.view_all_group_timetables"):
+        checker.prefetch_perms(classes)
+
+        wanted_classes = set()
+
+        for _class in classes:
+            if checker.has_perm("core.view_group_timetable", _class):
+                wanted_classes.add(_class.pk)
+
+        classes = classes.filter(
+            Q(pk__in=wanted_classes) | Q(members=user.person) | Q(pk=user.person.primary_group.pk)
+            if user.person.primary_group
+            else Q() | Q(owners=user.person)
+        )
+
+    return classes
+
+
+def get_rooms(user: User):
+    checker = ObjectPermissionChecker(user)
+
+    rooms = (
+        Room.objects.annotate(lessons_count=Count("lesson_periods"))
+        .filter(lessons_count__gt=0)
+        .order_by("short_name", "name")
+    )
+
+    if not check_global_permission(user, "chronos.view_all_room_timetables"):
+        checker.prefetch_perms(rooms)
+
+        wanted_rooms = set()
+
+        for room in rooms:
+            if checker.has_perm("chronos.view_room_timetable", room):
+                wanted_rooms.add(room.pk)
+
+        rooms = rooms.filter(Q(pk__in=wanted_rooms))
+
+    return rooms