Restructure our python module. A lot.

src/pretix/presale/middleware.py

@@ -0,0 +1,22 @@
+from django.core.urlresolvers import resolve
+from django.http import HttpResponseNotFound
+
+from pretix.base.models import Event
+
+
+class EventMiddleware:
+
+    def process_request(self, request):
+        url = resolve(request.path_info)
+        url_namespace = url.namespace
+        url_name = url.url_name
+        if url_namespace != 'presale':
+            return
+        if 'event.' in url_name and 'event' in url.kwargs:
+            try:
+                request.event = Event.objects.current.filter(
+                    slug=url.kwargs['event'],
+                    organizer__slug=url.kwargs['organizer'],
+                ).select_related('organizer')[0]
+            except IndexError:
+                return HttpResponseNotFound()  # TODO: Provide error message