Add fields to the observations endpoint required by the frontend, add…

… an observations/filters endpoint that returns the fields that observations can befiltered on, as well as the options for choice fields

observation_portal/observations/serializers.py

@@ -297,7 +297,8 @@ class ObservationSerializer(serializers.ModelSerializer):
 
     class Meta:
         model = Observation
-        fields = ('site', 'enclosure', 'telescope', 'start', 'end', 'priority', 'configuration_statuses', 'request')
+        fields = ('site', 'enclosure', 'telescope', 'start', 'end', 'priority', 'configuration_statuses', 'request', 'state', 'modified', 'created')
+        read_only_fields = ('state', 'modified', 'created')
 
     def validate(self, data):
         user = self.context['request'].user

observation_portal/observations/viewsets.py

@@ -68,6 +68,19 @@ class ObservationViewSet(CreateListModelMixin, ListAsDictMixin, viewsets.ModelVi
     def get_queryset(self):
         return observations_queryset(self.request).prefetch_related('request__windows', 'request__location').distinct()
 
+    @action(detail=False, methods=['get'])
+    def filters(self, request):
+        obs_filter_options = {'fields': [], 'choice_fields': []}
+        for filter_name, filter_field in self.filter_class.get_filters().items():
+            if hasattr(filter_field.field, 'choices'):
+                obs_filter_options['choice_fields'].append({
+                    'name': filter_name,
+                    'options': list(filter_field.field.choices)
+                })
+            else:
+                obs_filter_options['fields'].append(filter_name)
+        return Response(obs_filter_options, status=200)
+
     @action(detail=False, methods=['post'])
     def cancel(self, request):
         """