Rounding on payment method change

src/pretix/base/services/orders.py

@@ -3146,6 +3146,7 @@ def change_payment_provider(order: Order, payment_provider, amount=None, new_pay
         raise Exception('change_payment_provider should only be called in atomic transaction!')
 
     oldtotal = order.total
+    already_paid = order.payment_refund_sum
     e = OrderPayment.objects.filter(fee=OuterRef('pk'), state__in=(OrderPayment.PAYMENT_STATE_CONFIRMED,
                                                                    OrderPayment.PAYMENT_STATE_REFUNDED))
     open_fees = list(
@@ -3162,19 +3163,44 @@ def change_payment_provider(order: Order, payment_provider, amount=None, new_pay
         fee = OrderFee(fee_type=OrderFee.FEE_TYPE_PAYMENT, value=Decimal('0.00'), order=order)
     old_fee = fee.value
 
+    positions = list(order.positions.all())
+    fees = list(order.fees.all())
+    rounding_changed = set(apply_rounding(
+        order.tax_rounding_mode, order.event.currency, [*positions, *[f for f in fees if f.pk != fee.pk]]
+    ))
+    total_without_fee = sum(c.price for c in positions) + sum(f.value for f in fees if f.pk != fee.pk)
+    pending_sum_without_fee = max(Decimal("0.00"), total_without_fee - already_paid)
+
     new_fee = payment_provider.calculate_fee(
-        order.pending_sum - old_fee if amount is None else amount
+        pending_sum_without_fee if amount is None else amount
     )
     if new_fee:
         fee.value = new_fee
         fee.internal_type = payment_provider.identifier
         fee._calculate_tax()
+        if not fee.pk:
+            fees.append(fee)
         fee.save()
     else:
         if fee.pk:
             fee.delete()
+        if fee in fees:
+            fees.remove(fee)
         fee = None
 
+    rounding_changed |= set(apply_rounding(
+        order.tax_rounding_mode, order.event.currency, [*positions, *fees]
+    ))
+    for l in rounding_changed:
+        if isinstance(l, OrderPosition):
+            l.save(update_fields=[
+                "price", "price_includes_rounding_correction", "tax_value", "tax_value_includes_rounding_correction"
+            ])
+        elif isinstance(l, OrderFee):
+            l.save(update_fields=[
+                "value", "value_includes_rounding_correction", "tax_value", "tax_value_includes_rounding_correction"
+            ])
+
     open_payment = None
     if new_payment:
         lp = order.payments.select_for_update(of=OF_SELF).exclude(pk=new_payment.pk).last()
@@ -3201,7 +3227,7 @@ def change_payment_provider(order: Order, payment_provider, amount=None, new_pay
                 },
             )
 
-    order.total = (order.positions.aggregate(sum=Sum('price'))['sum'] or 0) + (order.fees.aggregate(sum=Sum('value'))['sum'] or 0)
+    order.total = sum(c.price for c in positions) + sum(f.value for f in fees)
     order.save(update_fields=['total'])
 
     if not new_payment:

src/pretix/presale/checkoutflow.py

@@ -1388,7 +1388,7 @@ class PaymentStep(CartMixin, TemplateFlowStep):
         ctx['cart'] = self.get_cart()
         ctx['current_payments'] = [
             p for p in self.current_selected_payments(
-                ctx['cart']['positions'], ctx['cart']['fees'], ctx['cart']['invoice_address'],
+                ctx['cart']['raw'], ctx['cart']['fees'], ctx['cart']['invoice_address'],
             )
             if p.get('multi_use_supported')
         ]
@@ -1430,7 +1430,6 @@ class PaymentStep(CartMixin, TemplateFlowStep):
         total = sum([c.price for c in cart]) + sum([f.value for f in fees])
 
         selected = self.current_selected_payments(cart, fees, self.invoice_address, warn=warn)
-        print(sum(p['payment_amount'] for p in selected), total)
         if sum(p['payment_amount'] for p in selected) != total:
             if warn:
                 messages.error(request, _('Please select a payment method to proceed.'))
@@ -1515,7 +1514,7 @@ class ConfirmStep(CartMixin, AsyncAction, TemplateFlowStep):
         ctx['cart'] = self.get_cart(answers=True)
 
         selected_payments = self.current_selected_payments(
-            ctx['cart']['positions'],
+            ctx['cart']['raw'],
             ctx['cart']['fees'],
             ctx['cart']['invoice_address'],
         )