New data model for default tax rule and new options for cancellation fees (#4962)

* New data model for default tax rule

* Remove misleading empty label when field is not optional

* Allow to split cancellation fee

* Fix API and tests

* Update migration

* Update src/tests/api/test_taxrules.py

Co-authored-by: luelista <weller@rami.io>

* Update src/tests/api/test_taxrules.py

Co-authored-by: luelista <weller@rami.io>

* Review note

* Update src/pretix/base/models/tax.py

Co-authored-by: luelista <weller@rami.io>

* Flip API behaviour for default

* Fix failing tests

* Fix failing test

* Split migration

---------

Co-authored-by: luelista <weller@rami.io>

src/pretix/control/views/event.py

@@ -68,7 +68,7 @@ from django.utils.http import url_has_allowed_host_and_scheme
 from django.utils.safestring import mark_safe
 from django.utils.timezone import now
 from django.utils.translation import gettext, gettext_lazy as _, gettext_noop
-from django.views.generic import FormView, ListView
+from django.views.generic import DetailView, FormView, ListView
 from django.views.generic.base import TemplateView, View
 from django.views.generic.detail import SingleObjectMixin
 from i18nfield.strings import LazyI18nString
@@ -1274,6 +1274,8 @@ class TaxCreate(EventSettingsViewMixin, EventPermissionRequiredMixin, CreateView
 
     @transaction.atomic
     def form_valid(self, form):
+        if not self.request.event.tax_rules.exists():
+            form.instance.default = True
         form.instance.event = self.request.event
         form.instance.custom_rules = json.dumps([
             f.cleaned_data for f in self.formset.ordered_forms if f not in self.formset.deleted_forms
@@ -1354,6 +1356,50 @@ class TaxUpdate(EventSettingsViewMixin, EventPermissionRequiredMixin, UpdateView
         return super().form_invalid(form)
 
 
+class TaxDefault(EventSettingsViewMixin, EventPermissionRequiredMixin, DetailView):
+    model = TaxRule
+    permission = 'can_change_event_settings'
+
+    def get_object(self, queryset=None) -> TaxRule:
+        try:
+            return self.request.event.tax_rules.get(
+                id=self.kwargs['rule']
+            )
+        except TaxRule.DoesNotExist:
+            raise Http404(_("The requested tax rule does not exist."))
+
+    def get(self, request, *args, **kwargs):
+        return self.http_method_not_allowed(request, *args, **kwargs)
+
+    @transaction.atomic
+    def post(self, request, *args, **kwargs):
+        messages.success(self.request, _('Your changes have been saved.'))
+        obj = self.get_object()
+        if not obj.default:
+            for tr in self.request.event.tax_rules.filter(default=True):
+                tr.log_action(
+                    'pretix.event.taxrule.changed', user=self.request.user, data={
+                        'default': False,
+                    }
+                )
+                tr.default = False
+                tr.save(update_fields=['default'])
+            obj.log_action(
+                'pretix.event.taxrule.changed', user=self.request.user, data={
+                    'default': True,
+                }
+            )
+            obj.default = True
+            obj.save(update_fields=['default'])
+        return redirect(self.get_success_url())
+
+    def get_success_url(self) -> str:
+        return reverse('control:event.settings.tax', kwargs={
+            'organizer': self.request.event.organizer.slug,
+            'event': self.request.event.slug,
+        })
+
+
 class TaxDelete(EventSettingsViewMixin, EventPermissionRequiredMixin, CompatDeleteView):
     model = TaxRule
     template_name = 'pretixcontrol/event/tax_delete.html'

src/pretix/control/views/main.py

@@ -181,8 +181,9 @@ class EventWizard(SafeSessionWizardView):
                 initial['location'] = self.clone_from.location
                 initial['timezone'] = self.clone_from.settings.timezone
                 initial['locale'] = self.clone_from.settings.locale
-                if self.clone_from.settings.tax_rate_default:
-                    initial['tax_rate'] = self.clone_from.settings.tax_rate_default.rate
+                tax_rule = self.clone_from.cached_default_tax_rule
+                if tax_rule:
+                    initial['tax_rate'] = tax_rule.rate
         if 'organizer' in self.request.GET:
             if step == 'foundation':
                 try:
@@ -325,10 +326,17 @@ class EventWizard(SafeSessionWizardView):
                 event.set_defaults()
 
             if basics_data['tax_rate'] is not None:
-                if not event.settings.tax_rate_default or event.settings.tax_rate_default.rate != basics_data['tax_rate']:
-                    event.settings.tax_rate_default = event.tax_rules.create(
+                if self.clone_from:
+                    default_tax_rule = self.clone_from.cached_default_tax_rule
+                elif copy_data and copy_data['copy_from_event']:
+                    default_tax_rule = from_event.cached_default_tax_rule
+                else:
+                    default_tax_rule = None
+                if not default_tax_rule or default_tax_rule.rate != basics_data['tax_rate']:
+                    event.tax_rules.create(
                         name=LazyI18nString.from_gettext(gettext('VAT')),
-                        rate=basics_data['tax_rate']
+                        rate=basics_data['tax_rate'],
+                        default=not default_tax_rule,
                     )
 
             event.settings.set('timezone', basics_data['timezone'])