Refs #314 -- Read-only REST API (#513)

* initial commit

* API auth

* Hierarchical URLs

* Add session auth

* Strong hierarchy

* Add filters

* Add i18n fields, questions

* More viewsets and serializers

* Ticket download

* Add OrderPosition serializer

* View-level permissions

* More tests

* More tests

* Add basic API docs

* Add REST API to docs frontpage

* Tests for order endpoints

* Add invoice tests

* Voucher and waitinglist tests

* Doc draft

* order docs

* Docs on all viewsets

* Disable DRF docs, style sphinx, style browsable API

* Fix tests

* deprecated imports

* Test foo

* Attendee names

* Fix migration problems

* Remove browsable API, plugin integration

* Doc fixes

src/pretix/api/views/voucher.py

@@ -0,0 +1,40 @@
+from django.db.models import F, Q
+from django.utils.timezone import now
+from django_filters.rest_framework import (
+    BooleanFilter, DjangoFilterBackend, FilterSet,
+)
+from rest_framework import viewsets
+from rest_framework.filters import OrderingFilter
+
+from pretix.api.serializers.voucher import VoucherSerializer
+from pretix.base.models import Voucher
+
+
+class VoucherFilter(FilterSet):
+    active = BooleanFilter(method='filter_active')
+
+    class Meta:
+        model = Voucher
+        fields = ['code', 'max_usages', 'redeemed', 'block_quota', 'allow_ignore_quota',
+                  'price_mode', 'value', 'item', 'variation', 'quota', 'tag']
+
+    def filter_active(self, queryset, name, value):
+        if value:
+            return queryset.filter(Q(redeemed__lt=F('max_usages')) &
+                                   (Q(valid_until__isnull=True) | Q(valid_until__gt=now())))
+        else:
+            return queryset.filter(Q(redeemed__gte=F('max_usages')) |
+                                   (Q(valid_until__isnull=False) & Q(valid_until__lte=now())))
+
+
+class VoucherViewSet(viewsets.ReadOnlyModelViewSet):
+    serializer_class = VoucherSerializer
+    queryset = Voucher.objects.none()
+    filter_backends = (DjangoFilterBackend, OrderingFilter)
+    ordering = ('id',)
+    ordering_fields = ('id', 'code', 'max_usages', 'valid_until', 'value')
+    filter_class = VoucherFilter
+    permission = 'can_view_vouchers'
+
+    def get_queryset(self):
+        return self.request.event.vouchers.all()