Add support for limiing to certain tracks

It's now possible to limit the public voting to certain tracks. This is
implemented as close as possible as the feature in pretalx where you
can limit tracks for certain review teams.

Related to pretalx#26.

pretalx_public_voting/forms.py

@@ -1,5 +1,6 @@
 from django import forms
 from django.utils.translation import gettext_lazy as _
+from django_scopes.forms import SafeModelMultipleChoiceField
 from i18nfield.forms import I18nModelForm
 from pretalx.common.urls import build_absolute_uri
 from pretalx.mail.models import QueuedMail
@@ -109,6 +110,7 @@ def save(self):
 class PublicVotingSettingsForm(I18nModelForm):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
+        self.fields["limit_tracks"].queryset = self.instance.event.tracks.all()
         minimum = self.instance.min_score
         maximum = self.instance.max_score
         for number in range(abs(maximum - minimum + 1)):
@@ -152,11 +154,16 @@ class Meta:
             "anonymize_speakers",
             "show_session_image",
             "show_session_description",
+            "limit_tracks",
             "allowed_emails",
             "min_score",
             "max_score",
         )
         widgets = {
             "start": forms.DateTimeInput(attrs={"class": "datetimepickerfield"}),
             "end": forms.DateTimeInput(attrs={"class": "datetimepickerfield"}),
+            "limit_tracks": forms.SelectMultiple(attrs={"class": "select2"}),
+        }
+        field_classes = {
+            "limit_tracks": SafeModelMultipleChoiceField,
         }

pretalx_public_voting/migrations/0006_publicvotingsettings_limit_tracks.py

@@ -0,0 +1,18 @@
+# Generated by Django 4.2.5 on 2023-09-29 19:47
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("submission", "0073_track_position"),
+        ("pretalx_public_voting", "0005_publicvotingsettings_show_session_description"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="publicvotingsettings",
+            name="limit_tracks",
+            field=models.ManyToManyField(to="submission.track"),
+        ),
+    ]

pretalx_public_voting/models.py

@@ -75,6 +75,9 @@ class PublicVotingSettings(models.Model):
             "You can limit who is allowed to cast a vote. Please enter one email address per line."
         ),
     )
+    limit_tracks = models.ManyToManyField(
+        to="submission.Track", verbose_name=_("Limit to tracks"), blank=True
+    )
 
     @cached_property
     def allowed_email_list(self):

pretalx_public_voting/views.py

@@ -79,6 +79,9 @@ def get_queryset(self):
         base_qs = self.request.event.submissions.all().filter(
             state=SubmissionStates.SUBMITTED
         )
+        tracks = self.request.event.public_vote_settings.limit_tracks.all()
+        if tracks:
+            base_qs = base_qs.filter(track__in=tracks)
         submission_pks = list(base_qs.values_list("pk", flat=True))
         random.seed(self.hashed_email)
         random.shuffle(submission_pks)