Order change: Allow price reduction as long as no refund is required (Z#23135268) (#3689)

* Order change: Allow price reduction as long as no refund is required

* Update src/pretix/base/settings.py

Co-authored-by: Richard Schreiber <schreiber@rami.io>

---------

Co-authored-by: Richard Schreiber <schreiber@rami.io>

src/pretix/base/settings.py

@@ -1677,6 +1677,8 @@ DEFAULTS = {
                 ('gte', _('Only allow changes if the resulting price is higher or equal than the previous price.')),
                 ('gt', _('Only allow changes if the resulting price is higher than the previous price.')),
                 ('eq', _('Only allow changes if the resulting price is equal to the previous price.')),
+                ('gte_paid', _('Allow changes regardless of price, as long as no refund is required (i.e. the resulting '
+                               'price is not lower than what has already been paid).')),
                 ('any', _('Allow changes regardless of price, even if this results in a refund.')),
             )
         ),

src/pretix/presale/views/order.py

@@ -1595,6 +1595,8 @@ class OrderChangeMixin:
             raise OrderError(_('You may only change your order in a way that increases the total price.'))
         if ocm._totaldiff != Decimal('0.00') and pr == 'eq':
             raise OrderError(_('You may not change your order in a way that changes the total price.'))
+        if ocm._totaldiff < Decimal('0.00') and self.order.total + ocm._totaldiff < self.order.payment_refund_sum and pr == 'gte_paid':
+            raise OrderError(_('You may not change your order in a way that would require a refund.'))
 
         if ocm._totaldiff > Decimal('0.00') and self.order.status == Order.STATUS_PAID:
             self.order.set_expires(

src/tests/presale/test_order_change.py

@@ -1434,6 +1434,53 @@ class OrderChangeAddonsTest(BaseOrdersTest):
         self.order.refresh_from_db()
         assert self.order.total == Decimal('35.00')
 
+    def test_allow_user_price_gte_paid(self):
+        self.event.settings.change_allow_user_price = 'gte_paid'
+        with scopes_disabled():
+            OrderPosition.objects.create(
+                order=self.order,
+                item=self.workshop1,
+                variation=None,
+                price=Decimal("12"),
+                addon_to=self.ticket_pos,
+                attendee_name_parts={'full_name': "Peter"}
+            )
+            self.order.total += Decimal("12")
+            self.order.save()
+            self.order.payments.create(amount=Decimal("23"), provider="manual", state=OrderPayment.PAYMENT_STATE_CONFIRMED)
+
+        response = self.client.post(
+            '/%s/%s/order/%s/%s/change' % (self.orga.slug, self.event.slug, self.order.code, self.order.secret),
+            {
+            },
+            follow=True
+        )
+        assert 'alert-danger' not in response.content.decode()
+
+        with scopes_disabled():
+            self.order.payments.create(amount=Decimal("12"), provider="manual", state=OrderPayment.PAYMENT_STATE_CONFIRMED)
+
+        response = self.client.post(
+            '/%s/%s/order/%s/%s/change' % (self.orga.slug, self.event.slug, self.order.code, self.order.secret),
+            {
+            },
+            follow=True
+        )
+        assert 'alert-danger' in response.content.decode()
+        assert 'refund' in response.content.decode()
+
+        response = self.client.post(
+            '/%s/%s/order/%s/%s/change' % (self.orga.slug, self.event.slug, self.order.code, self.order.secret),
+            {
+                'confirm': 'true'
+            },
+            follow=True
+        )
+        assert 'alert-danger' in response.content.decode()
+        assert 'refund' in response.content.decode()
+        self.order.refresh_from_db()
+        assert self.order.total == Decimal('35.00')
+
     def test_allow_user_price_eq(self):
         self.event.settings.change_allow_user_price = 'eq'
         response = self.client.post(