Refs #654 -- Writable API methods for waiting list entries (#885)

* Refs #654 -- Writable API methods for waiting list entries

* Update test_waitinglist.py

src/pretix/api/serializers/waitinglist.py

@@ -1,3 +1,5 @@
+from rest_framework.exceptions import ValidationError
+
 from pretix.api.serializers.i18n import I18nAwareModelSerializer
 from pretix.base.models import WaitingListEntry
 
@@ -7,3 +9,27 @@ class WaitingListSerializer(I18nAwareModelSerializer):
     class Meta:
         model = WaitingListEntry
         fields = ('id', 'created', 'email', 'voucher', 'item', 'variation', 'locale', 'subevent')
+        read_only_fields = ('id', 'created', 'voucher')
+
+    def validate(self, data):
+        data = super().validate(data)
+        event = self.context['event']
+
+        full_data = self.to_internal_value(self.to_representation(self.instance)) if self.instance else {}
+        full_data.update(data)
+
+        WaitingListEntry.clean_duplicate(full_data.get('email'), full_data.get('item'), full_data.get('variation'),
+                                         full_data.get('subevent'), self.instance.pk if self.instance else None)
+        WaitingListEntry.clean_itemvar(event, full_data.get('item'), full_data.get('variation'))
+        WaitingListEntry.clean_subevent(event, full_data.get('subevent'))
+
+        if 'item' in data or 'variation' in data:
+            availability = (
+                full_data.get('variation').check_quotas(count_waitinglist=True, subevent=full_data.get('subevent'))
+                if full_data.get('variation')
+                else full_data.get('item').check_quotas(count_waitinglist=True, subevent=full_data.get('subevent'))
+            )
+            if availability[0] == 100:
+                raise ValidationError("This product is currently available.")
+
+        return data