Allow to keep cancellation fees (#1130)

* Allow to keep cancellation fees

* Add tests and clarifications

* Add API

src/pretix/control/forms/orders.py

@@ -77,6 +77,40 @@ class ConfirmPaymentForm(forms.Form):
             del self.fields['force']
 
 
+class CancelForm(ConfirmPaymentForm):
+    send_email = forms.BooleanField(
+        required=False,
+        label=_('Notify user by e-mail'),
+        initial=True
+    )
+    cancellation_fee = forms.DecimalField(
+        required=False,
+        max_digits=10, decimal_places=2,
+        localize=True,
+        label=_('Keep a cancellation fee of'),
+        help_text=_('If you keep a fee, all positions within this order will be canceled and the order will be reduced '
+                    'to a paid cancellation fee. Payment and shipping fees will be canceled as well, so include them '
+                    'in your cancellation fee if you want to keep them. Please always enter a gross value, '
+                    'tax will be calculated automatically.'),
+    )
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        prs = self.instance.payment_refund_sum
+        if prs > 0:
+            change_decimal_field(self.fields['cancellation_fee'], self.instance.event.currency)
+            self.fields['cancellation_fee'].initial = Decimal('0.00')
+            self.fields['cancellation_fee'].max_value = prs
+        else:
+            del self.fields['cancellation_fee']
+
+    def clean_cancellation_fee(self):
+        val = self.cleaned_data['cancellation_fee']
+        if val > self.instance.payment_refund_sum:
+            raise ValidationError(_('The cancellation fee cannot be higher than the payment credit of this order.'))
+        return val
+
+
 class MarkPaidForm(ConfirmPaymentForm):
     amount = forms.DecimalField(
         required=True,

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

@@ -1,5 +1,6 @@
 {% extends "pretixcontrol/event/base.html" %}
 {% load i18n %}
+{% load bootstrap3 %}
 {% block title %}
     {% trans "Cancel order" %}
 {% endblock %}
@@ -17,15 +18,14 @@
         {% endblocktrans %}</p>
     {% endif %}
 
-    <form method="post" href="">
+    <form method="post" href="" class="">
         {% csrf_token %}
         <input type="hidden" name="status" value="c"/>
-        <div class="checkbox">
-            <label>
-                <input type="checkbox" name="send_email" value="on" checked="checked">
-                {% trans "Notify user by e-mail" %}
-            </label>
-        </div>
+        {% bootstrap_form_errors form %}
+        {% bootstrap_field form.send_email layout='' %}
+        {% if form.cancellation_fee %}
+            {% bootstrap_field form.cancellation_fee layout='' %}
+        {% endif %}
         <div class="row checkout-button-row">
             <div class="col-md-4">
                 <a class="btn btn-block btn-default btn-lg"

src/pretix/control/views/orders.py

@@ -62,9 +62,10 @@ from pretix.base.views.mixins import OrderQuestionsViewMixin
 from pretix.base.views.tasks import AsyncAction
 from pretix.control.forms.filter import EventOrderFilterForm, RefundFilterForm
 from pretix.control.forms.orders import (
-    CommentForm, ConfirmPaymentForm, ExporterForm, ExtendForm, MarkPaidForm,
-    OrderContactForm, OrderLocaleForm, OrderMailForm, OrderPositionAddForm,
-    OrderPositionChangeForm, OrderRefundForm, OtherOperationsForm,
+    CancelForm, CommentForm, ConfirmPaymentForm, ExporterForm, ExtendForm,
+    MarkPaidForm, OrderContactForm, OrderLocaleForm, OrderMailForm,
+    OrderPositionAddForm, OrderPositionChangeForm, OrderRefundForm,
+    OtherOperationsForm,
 )
 from pretix.control.permissions import EventPermissionRequiredMixin
 from pretix.control.views import PaginationMixin
@@ -772,7 +773,10 @@ class OrderRefundView(OrderView):
             'payments': payments,
             'remainder': to_refund,
             'order': self.order,
-            'partial_amount': self.request.POST.get('start-partial_amount'),
+            'partial_amount': (
+                self.request.POST.get('start-partial_amount') if self.request.method == 'POST'
+                else self.request.GET.get('start-partial_amount')
+            ),
             'start_form': self.start_form
         })
 
@@ -800,6 +804,13 @@ class OrderTransition(OrderView):
             data=self.request.POST if self.request.method == "POST" else None,
         )
 
+    @cached_property
+    def mark_canceled_form(self):
+        return CancelForm(
+            instance=self.order,
+            data=self.request.POST if self.request.method == "POST" else None,
+        )
+
     def post(self, *args, **kwargs):
         to = self.request.POST.get('status', '')
         if self.order.status in (Order.STATUS_PENDING, Order.STATUS_EXPIRED) and to == 'p' and self.mark_paid_form.is_valid():
@@ -847,8 +858,10 @@ class OrderTransition(OrderView):
                                                  'confirmation mail.'))
             else:
                 messages.success(self.request, _('The payment has been created successfully.'))
-        elif self.order.cancel_allowed() and to == 'c':
-            cancel_order(self.order, user=self.request.user, send_mail=self.request.POST.get("send_email") == "on")
+        elif self.order.cancel_allowed() and to == 'c' and self.mark_canceled_form.is_valid():
+            cancel_order(self.order, user=self.request.user,
+                         send_mail=self.mark_canceled_form.cleaned_data['send_email'],
+                         cancellation_fee=self.mark_canceled_form.cleaned_data.get('cancellation_fee'))
             self.order.refresh_from_db()
 
             if self.order.pending_sum < 0:
@@ -877,6 +890,7 @@ class OrderTransition(OrderView):
             })
         elif self.order.cancel_allowed() and to == 'c':
             return render(self.request, 'pretixcontrol/order/cancel.html', {
+                'form': self.mark_canceled_form,
                 'order': self.order,
             })
         else: