Refactor cancelling positions and orders in the data model (#1088)

- [x] Data model
- [x] display in order view in backend
- [x] review all usages of OrderPositions.objects
- [x] review all usages of order.positions
- [x] review all other model usages
- [x] review plugins
- [x] plugins backwards-compatible API?
- [x] decide on way forward for REST API
- [x] need to cancel fees
- [x] tests
- [ ] plugins
  - [ ] gdpr
  - [ ] reports
- [x] docs

src/pretix/base/services/orders.py

@@ -124,25 +124,12 @@ def extend_order(order: Order, new_date: datetime, force: bool=False, user: User
 
 @transaction.atomic
 def mark_order_refunded(order, user=None, auth=None, api_token=None):
-    """
-    Mark this order as refunded. This sets the payment status and returns the order object.
-    :param order: The order to change
-    :param user: The user that performed the change
-    """
-    if isinstance(order, int):
-        order = Order.objects.get(pk=order)
-    if isinstance(user, int):
-        user = User.objects.get(pk=user)
-    with order.event.lock():
-        order.status = Order.STATUS_REFUNDED
-        order.save(update_fields=['status'])
-
-    order.log_action('pretix.event.order.refunded', user=user, auth=auth or api_token)
-    i = order.invoices.filter(is_cancellation=False).last()
-    if i:
-        generate_cancellation(i)
-
-    return order
+    oautha = auth.pk if isinstance(auth, OAuthApplication) else None
+    device = auth.pk if isinstance(auth, Device) else None
+    api_token = (api_token.pk if api_token else None) or (auth if isinstance(auth, TeamAPIToken) else None)
+    return _cancel_order(
+        order.pk, user.pk if user else None, send_mail=False, api_token=api_token, device=device, oauth_application=oautha
+    )
 
 
 @transaction.atomic
@@ -1043,7 +1030,10 @@ class OrderChangeManager:
                         'addon_to': opa.addon_to_id,
                         'old_price': opa.price,
                     })
-                    opa.delete()
+                    opa.canceled = True
+                    if opa.voucher:
+                        Voucher.objects.filter(pk=opa.voucher.pk).update(redeemed=F('redeemed') - 1)
+                    opa.save(update_fields=['canceled'])
                 self.order.log_action('pretix.event.order.changed.cancel', user=self.user, auth=self.auth, data={
                     'position': op.position.pk,
                     'positionid': op.position.positionid,
@@ -1052,7 +1042,10 @@ class OrderChangeManager:
                     'old_price': op.position.price,
                     'addon_to': None,
                 })
-                op.position.delete()
+                op.position.canceled = True
+                if op.position.voucher:
+                    Voucher.objects.filter(pk=op.position.voucher.pk).update(redeemed=F('redeemed') - 1)
+                op.position.save(update_fields=['canceled'])
             elif isinstance(op, self.AddOperation):
                 pos = OrderPosition.objects.create(
                     item=op.item, variation=op.variation, addon_to=op.addon_to,
@@ -1117,7 +1110,7 @@ class OrderChangeManager:
         except InvoiceAddress.DoesNotExist:
             pass
 
-        split_order.total = sum([p.price for p in split_positions])
+        split_order.total = sum([p.price for p in split_positions if not p.canceled])
         if split_order.total != Decimal('0.00') and self.order.status != Order.STATUS_PAID:
             pp = self._get_payment_provider()
             if pp:
@@ -1180,7 +1173,7 @@ class OrderChangeManager:
         return payment_sum - refund_sum
 
     def _recalculate_total_and_payment_fee(self):
-        total = sum([p.price for p in self.order.positions.all()]) + sum([f.value for f in self.order.fees.all()])
+        total = sum([p.price for p in self.order.positions.all() if not p.canceled]) + sum([f.value for f in self.order.fees.all()])
         payment_fee = Decimal('0.00')
         if self.open_payment:
             current_fee = Decimal('0.00')