Disallow creating lesson documentation for lessons in the future. Close #30.

Closes #30 (closed)

biscuit/apps/alsijil/views.py

 from collections import OrderedDict
-from datetime import date, timedelta
+from datetime import date, datetime, timedelta
 from typing import Optional
 
 from django.contrib.auth.decorators import login_required
+from django.core.exceptions import PermissionDenied
 from django.db.models import Count, Exists, F, OuterRef, Q, Sum
 from django.http import Http404, HttpRequest, HttpResponse
 from django.shortcuts import get_object_or_404, render
@@ -35,6 +36,9 @@ def lesson(request: HttpRequest, year: Optional[int] = None, week: Optional[int]
     if not lesson_period:
         raise Http404(_('You either selected an invalid lesson or there is currently no lesson in progress.'))
 
+    if datetime.combine(wanted_week[lesson_period.period.weekday - 1], lesson_period.period.time_start) < datetime.now():
+        raise PermissionDenied(_('You are not allowed to create a lesson documentation for a lesson in the future.'))
+
     context['lesson_period'] = lesson_period
     context['week'] = wanted_week
     context['day'] = wanted_week[lesson_period.period.weekday - 1]