Refs #340 -- Allow order changes for paid orders if they don't change the total

src/pretix/base/models/items.py

@@ -309,6 +309,10 @@ class ItemVariation(models.Model):
     def __str__(self):
         return str(self.value)
 
+    @property
+    def price(self):
+        return self.default_price if self.default_price is not None else self.item.default_price
+
     def delete(self, *args, **kwargs):
         super().delete(*args, **kwargs)
         if self.item:

src/pretix/base/models/orders.py

@@ -190,6 +190,10 @@ class Order(LoggedModel):
         """
         return '{event}-{code}'.format(event=self.event.slug.upper(), code=self.code)
 
+    @property
+    def changable(self):
+        return self.status in (Order.STATUS_PAID, Order.STATUS_PENDING)
+
     def save(self, *args, **kwargs):
         if not self.code:
             self.assign_code()

src/pretix/base/services/orders.py

@@ -480,9 +480,11 @@ class OrderChangeManager:
         'quota': _('The quota {name} does not have enough capacity left to perform the operation.'),
         'product_invalid': _('The selected product is not active or has no price set.'),
         'complete_cancel': _('This operation would leave the order empty. Please cancel the order itself instead.'),
-        'not_pending': _('Only pending orders can be changed.'),
+        'not_pending_or_paid': _('Only pending or paid orders can be changed.'),
         'paid_to_free_exceeded': _('This operation would make the order free and therefore immediately paid, however '
                                    'no quota is available.'),
+        'paid_price_change': _('Currently, paid orders can only be changed in a way that does not change the total '
+                               'price of the order as partial payments or refunds are not yet supported.')
     }
     ItemOperation = namedtuple('ItemOperation', ('position', 'item', 'variation', 'price'))
     PriceOperation = namedtuple('PriceOperation', ('position', 'price'))
@@ -498,8 +500,7 @@ class OrderChangeManager:
     def change_item(self, position: OrderPosition, item: Item, variation: Optional[ItemVariation]):
         if (not variation and item.has_variations) or (variation and variation.item_id != item.pk):
             raise OrderError(self.error_messages['product_without_variation'])
-        price = item.default_price if variation is None else (
+        price = item.default_price if variation is None else variation.price
-            variation.default_price if variation.default_price is not None else item.default_price)
         if not price:
             raise OrderError(self.error_messages['product_invalid'])
         self._totaldiff = price - position.price
@@ -528,6 +529,10 @@ class OrderChangeManager:
         if self.order.total == Decimal('0.00') and self._totaldiff > 0:
             raise OrderError(self.error_messages['free_to_paid'])
 
+    def _check_paid_price_change(self):
+        if self.order.status == Order.STATUS_PAID and self._totaldiff != 0:
+            raise OrderError(self.error_messages['paid_price_change'])
+
     def _check_paid_to_free(self):
         if self.order.total == 0:
             try:
@@ -624,9 +629,10 @@ class OrderChangeManager:
             return
         with transaction.atomic():
             with self.order.event.lock():
-                if self.order.status != Order.STATUS_PENDING:
+                if self.order.status not in (Order.STATUS_PENDING, Order.STATUS_PAID):
-                    raise OrderError(self.error_messages['not_pending'])
+                    raise OrderError(self.error_messages['not_pending_or_paid'])
                 self._check_free_to_paid()
+                self._check_paid_price_change()
                 self._check_quotas()
                 self._check_complete_cancel()
                 self._perform_operations()

src/pretix/control/forms/orders.py

@@ -1,6 +1,7 @@
 from django import forms
 from django.core.exceptions import ValidationError
 from django.db import models
+from django.utils.formats import localize
 from django.utils.timezone import now
 from django.utils.translation import ugettext_lazy as _
 
@@ -94,9 +95,12 @@ class OrderPositionChangeForm(forms.Form):
             variations = list(i.variations.all())
             if variations:
                 for v in variations:
-                    choices.append(('%d-%d' % (i.pk, v.pk), '%s – %s' % (pname, v.value)))
+                    choices.append(('%d-%d' % (i.pk, v.pk),
+                                    '%s – %s (%s %s)' % (pname, v.value, localize(v.price),
+                                                         instance.order.event.currency)))
             else:
-                choices.append((str(i.pk), pname))
+                choices.append((str(i.pk), '%s (%s %s)' % (pname, localize(i.default_price),
+                                                           instance.order.event.currency)))
         self.fields['itemvar'].choices = choices
 
     def clean(self):

src/pretix/control/templates/pretixcontrol/order/index.html

@@ -144,7 +144,7 @@
             <div class="panel panel-default items">
                 <div class="panel-heading">
                     <div class="pull-right">
-                        {% if order.status == "n" and request.eventperm.can_change_orders %}
+                        {% if order.changable and request.eventperm.can_change_orders %}
                             <a href="{% url "control:event.order.change" event=request.event.slug organizer=request.event.organizer.slug code=order.code %}">
                                 <span class="fa fa-edit"></span>
                                 {% trans "Change products" %}

src/pretix/control/views/orders.py

@@ -446,8 +446,8 @@ class OrderChange(OrderView):
     template_name = 'pretixcontrol/order/change.html'
 
     def dispatch(self, request, *args, **kwargs):
-        if self.order.status != Order.STATUS_PENDING:
+        if self.order.status not in (Order.STATUS_PENDING, Order.STATUS_PAID):
-            messages.error(self.request, _('This action is only allowed for pending orders.'))
+            messages.error(self.request, _('This action is only allowed for pending or paid orders.'))
             return self._redirect_back()
         return super().dispatch(request, *args, **kwargs)
 

src/tests/base/test_orders.py

@@ -140,6 +140,8 @@ class OrderChangeManagerTests(TestCase):
         )
         self.ticket = Item.objects.create(event=self.event, name='Early-bird ticket', tax_rate=Decimal('7.00'),
                                           default_price=Decimal('23.00'), admission=True)
+        self.ticket2 = Item.objects.create(event=self.event, name='Other ticket', tax_rate=Decimal('7.00'),
+                                           default_price=Decimal('23.00'), admission=True)
         self.shirt = Item.objects.create(event=self.event, name='T-Shirt', tax_rate=Decimal('19.00'),
                                          default_price=Decimal('12.00'))
         self.op1 = OrderPosition.objects.create(
@@ -303,3 +305,22 @@ class OrderChangeManagerTests(TestCase):
         assert self.order.total == 0
         assert self.order.status == Order.STATUS_PAID
         assert self.order.payment_provider == 'free'
+
+    def test_change_paid_same_price(self):
+        self.order.status = Order.STATUS_PAID
+        self.order.save()
+        self.ocm.change_item(self.op1, self.ticket2, None)
+        self.ocm.commit()
+        self.order.refresh_from_db()
+        assert self.order.total == 46
+        assert self.order.status == Order.STATUS_PAID
+
+    def test_change_paid_different_price(self):
+        self.order.status = Order.STATUS_PAID
+        self.order.save()
+        self.ocm.change_price(self.op1, Decimal('5.00'))
+        with self.assertRaises(OrderError):
+            self.ocm.commit()
+        self.order.refresh_from_db()
+        assert self.order.total == 46
+        assert self.order.status == Order.STATUS_PAID