refactor: use django_filters FilterSet for APIShowViewSet

This change re-implements all existing collection filters for the
APIShowViewSet with a FilterSet. No breaking changes are expected,
though there are some changes in semantics:

* The owner, host, musicfocus, language, category, and topic
  filters now accept multiple values (i.e. ?category=2,3)
* The owner, host, musicfocus, language, category, topic, and type
  filter values are now validated and may be rejected as invalid if
  the referenced object does not exist.

program/filters.py

+from django_filters import rest_framework as filters
+from django_filters import widgets
+
+from django.contrib.auth.models import User
+from django.db.models import Q, QuerySet
+from django.utils import timezone
+from program import models
+
+
+class StaticFilterHelpTextMixin:
+    @classmethod
+    def filter_for_field(cls, field, field_name, lookup_expr=None):
+        _filter = super().filter_for_field(field, field_name, lookup_expr)
+        if "help_text" not in _filter.extra:
+            help_texts = getattr(cls.Meta, "help_texts", {})
+            _filter.extra["help_text"] = help_texts.get(field_name, "")
+        return _filter
+
+
+class ModelMultipleChoiceFilter(filters.ModelMultipleChoiceFilter):
+    def __init__(self, *args, **kwargs):
+        kwargs.setdefault("widget", widgets.CSVWidget())
+        kwargs["lookup_expr"] = "in"
+        super().__init__(*args, **kwargs)
+
+    def get_filter_predicate(self, v):
+        # There is something wrong with using ModelMultipleChoiceFilter
+        # along the CSVWidget that causes lookups to fail.
+        # May be related to: https://github.com/carltongibson/django-filter/issues/1103
+        return super().get_filter_predicate([v.pk])
+
+
+class ShowFilterSet(StaticFilterHelpTextMixin, filters.FilterSet):
+    active = filters.BooleanFilter(
+        field_name="is_active",
+        method="filter_active",
+        help_text=(
+            "Return only currently running shows if true or past or upcoming shows if false.",
+        ),
+    )
+    host = ModelMultipleChoiceFilter(
+        queryset=models.Host.objects.all(),
+        field_name="hosts",
+        help_text="Return only shows assigned to the given host(s).",
+    )
+    # TODO: replace `musicfocus` with `music_focus` when dashboard is updated
+    musicfocus = ModelMultipleChoiceFilter(
+        queryset=models.MusicFocus.objects.all(),
+        field_name="music_focus",
+        help_text="Return only shows with given music focus(es).",
+    )
+    owner = ModelMultipleChoiceFilter(
+        queryset=User.objects.all(),
+        field_name="owners",
+        help_text="Return only shows that belong to the given owner(s).",
+    )
+    category = ModelMultipleChoiceFilter(
+        queryset=models.Category.objects.all(),
+        help_text="Return only shows of the given category or categories.",
+    )
+    language = ModelMultipleChoiceFilter(
+        queryset=models.Language.objects.all(),
+        help_text="Return only shows of the given language(s).",
+    )
+    topic = ModelMultipleChoiceFilter(
+        queryset=models.Topic.objects.all(),
+        help_text="Return only shows of the given topic(s).",
+    )
+    public = filters.BooleanFilter(
+        field_name="is_public",
+        help_text="Return only shows that are public/non-public.",
+    )
+
+    def filter_active(self, queryset: QuerySet, name: str, value: bool):
+        # Filter currently running shows
+        # Get currently running schedules to filter by first
+        # For single dates we test if there'll be one in the future (and ignore the until date)
+        # TODO: Really consider first_date? (=currently active, not just upcoming ones)
+        # Add limit for future?
+        show_ids = (
+            models.Schedule.objects.filter(
+                Q(
+                    rrule_id__gt=1,
+                    first_date__lte=timezone.now(),
+                    last_date__gte=timezone.now(),
+                )
+                | Q(rrule_id=1, first_date__gte=timezone.now())
+            )
+            .distinct()
+            .values_list("show_id", flat=True)
+        )
+        if value:
+            # Filter active shows based on timeslots as well as on the is_active flag
+            # Even if there are future timeslots but is_active=True the show will be considered as
+            # inactive
+            return queryset.filter(id__in=show_ids, is_active=True)
+        else:
+            return queryset.exclude(id__in=show_ids, is_active=True)
+
+    class Meta:
+        model = models.Show
+        help_texts = {
+            "type": "Return only shows of a given type.",
+        }
+        fields = [
+            "active",
+            "category",
+            "host",
+            "language",
+            "musicfocus",
+            "owner",
+            "public",
+            "topic",
+            "type",
+        ]

program/views.py

@@ -27,11 +27,11 @@ from rest_framework.pagination import LimitOffsetPagination
 from rest_framework.response import Response
 
 from django.contrib.auth.models import User
-from django.db.models import Q
 from django.http import HttpResponse
 from django.shortcuts import get_object_or_404
 from django.utils import timezone
 from django.utils.translation import gettext as _
+from program import filters
 from program.models import (
     Category,
     FundingCategory,
@@ -264,106 +264,21 @@ class APIUserViewSet(viewsets.ModelViewSet):
 
 class APIShowViewSet(viewsets.ModelViewSet):
     """
-    /shows/ returns all shows (GET, POST)
-    /shows/?active=true returns all active shows (= currently running) (GET)
-    /shows/?active=false returns all inactive shows (= past or upcoming) (GET)
-    /shows/?public=true returns all public shows (GET)
-    /shows/?public=false returns all non-public shows (GET)
-    /shows/?host={host_pk} returns shows assigned to a given host (GET)
-    /shows/?owner={owner_pk} returns shows of a given owner (GET)
-    /shows/?language={language_pk} returns shows in a given language (GET)
-    /shows/?type={type_pk} returns shows of a given type (GET)
-    /shows/?category={category_pk} returns shows of a given category (GET)
-    /shows/?topic={topic_pk} returns shows of a given topic (GET)
-    /shows/?musicfocus={musicfocus_pk} returns shows of a given music focus (GET)
-    /shows/{pk|slug} retrieves or updates (if owned) a single show (GET, PUT).
-
-    Only superusers may add and delete shows
+    Returns a list of available shows.
+    Only superusers may add and delete shows.
     """
 
-    queryset = Show.objects.none()
+    queryset = Show.objects.all()
     serializer_class = ShowSerializer
     permission_classes = [permissions.DjangoModelPermissionsOrAnonReadOnly]
     pagination_class = LimitOffsetPagination
-
-    def get_queryset(self):
-        shows = Show.objects.all()
-
-        # Filters
-        if (
-            self.request.query_params.get("active") == "true"
-            or self.request.query_params.get("active") == "false"
-        ):
-            # Filter currently running shows
-            # Get currently running schedules to filter by first
-            # For single dates we test if there'll be one in the future (and ignore the until date)
-            # TODO: Really consider first_date? (=currently active, not just upcoming ones)
-            # Add limit for future?
-            show_ids = (
-                Schedule.objects.filter(
-                    Q(
-                        rrule_id__gt=1,
-                        first_date__lte=timezone.now(),
-                        last_date__gte=timezone.now(),
-                    )
-                    | Q(rrule_id=1, first_date__gte=timezone.now())
-                )
-                .distinct()
-                .values_list("show_id", flat=True)
-            )
-
-            # Filter active shows based on timeslots as well as on the is_active flag
-            # Even if there are future timeslots but is_active=True the show will be considered as
-            # inactive
-            shows = Show.objects.filter(id__in=show_ids, is_active=True)
-
-        if self.request.query_params.get("active") == "false":
-            # Return all shows except those which are running
-            shows = Show.objects.exclude(id__in=show_ids, is_active=True)
-
-        if self.request.query_params.get("public") == "true":
-            # Return all public shows
-            shows = shows.filter(is_public=True)
-
-        if self.request.query_params.get("public") == "false":
-            # Return all public shows
-            shows = shows.filter(is_public=False)
-
-        if owner := self.request.query_params.get("owner"):
-            if owner != "undefined":
-                shows = shows.filter(owners__in=[int(owner)])
-
-        if host := self.request.query_params.get("host"):
-            if host != "undefined":
-                shows = shows.filter(hosts__in=[int(host)])
-
-        if language := self.request.query_params.get("language"):
-            if language != "undefined":
-                shows = shows.filter(language__in=[int(language)])
-
-        if type_ := self.request.query_params.get("type"):
-            if type_ != "undefined":
-                shows = shows.filter(type__in=[int(type_)])
-
-        if category := self.request.query_params.get("category"):
-            if category != "undefined":
-                shows = shows.filter(category__in=[int(category)])
-
-        if topic := self.request.query_params.get("topic"):
-            if topic != "undefined":
-                shows = shows.filter(topic__in=[int(topic)])
-
-        # TODO: replace `musicfocus` with `music_focus` when dashboard is updated
-        if music_focus := self.request.query_params.get("musicfocus"):
-            if music_focus != "undefined":
-                shows = shows.filter(music_focus__in=[int(music_focus)])
-
-        return shows
+    filterset_class = filters.ShowFilterSet
 
     def create(self, request, *args, **kwargs):
         """
-        Create a show
-        Only superusers may create a show
+        Create a show.
+
+        Only superusers may create a show.
         """
 
         if not request.user.is_superuser:
@@ -396,8 +311,9 @@ class APIShowViewSet(viewsets.ModelViewSet):
 
     def update(self, request, *args, **kwargs):
         """
-        Update a show
-        Common users may only update shows they own
+        Update a show.
+
+        Common users may only update shows they own.
         """
 
         pk = get_values(self.kwargs, "pk")
@@ -423,8 +339,9 @@ class APIShowViewSet(viewsets.ModelViewSet):
 
     def destroy(self, request, *args, **kwargs):
         """
-        Delete a show
-        Only superusers may delete shows
+        Delete a show.
+
+        Only superusers may delete shows.
         """
 
         if not request.user.is_superuser: