Fix #163 -- Form to change orders (#191)

src/pretix/control/forms/event.py

@@ -329,6 +329,12 @@ class MailSettingsForm(SettingsForm):
         widget=I18nTextarea,
         help_text=_("Available placeholders: {event}, {url}")
     )
+    mail_text_order_changed = I18nFormField(
+        label=_("Changed order"),
+        required=False,
+        widget=I18nTextarea,
+        help_text=_("Available placeholders: {event}, {url}")
+    )
     mail_text_resend_link = I18nFormField(
         label=_("Resend link"),
         required=False,

src/pretix/control/forms/orders.py

@@ -1,8 +1,10 @@
 from django import forms
+from django.core.exceptions import ValidationError
 from django.db import models
+from django.utils.translation import ugettext_lazy as _
 
 from pretix.base.forms import I18nModelForm
-from pretix.base.models import Order
+from pretix.base.models import Item, Order
 
 
 class ExtendForm(I18nModelForm):
@@ -35,3 +37,54 @@ class CommentForm(I18nModelForm):
                 'class': 'helper-width-100',
             }),
         }
+
+
+class OrderPositionChangeForm(forms.Form):
+    itemvar = forms.ChoiceField()
+    price = forms.DecimalField(
+        required=False,
+        max_digits=10, decimal_places=2,
+        label=_('New price')
+    )
+    operation = forms.ChoiceField(
+        required=False,
+        widget=forms.RadioSelect,
+        choices=(
+            ('product', 'Change product'),
+            ('price', 'Change price'),
+            ('cancel', 'Remove product')
+        )
+    )
+
+    def __init__(self, *args, **kwargs):
+        instance = kwargs.pop('instance')
+        initial = kwargs.get('initial', {})
+        if instance:
+            try:
+                if instance.variation:
+                    initial['itemvar'] = '%d-%d' % (instance.item.pk, instance.variation.pk)
+                elif instance.item:
+                    initial['itemvar'] = str(instance.item.pk)
+            except Item.DoesNotExist:
+                pass
+
+            initial['price'] = instance.price
+
+        kwargs['initial'] = initial
+        super().__init__(*args, **kwargs)
+        choices = []
+        for i in instance.order.event.items.prefetch_related('variations').all():
+            pname = i.name
+            if not i.is_available():
+                pname += ' ({})'.format(_('inactive'))
+            variations = list(i.variations.all())
+            if variations:
+                for v in variations:
+                    choices.append(('%d-%d' % (i.pk, v.pk), '%s – %s' % (pname, v.value)))
+            else:
+                choices.append((str(i.pk), pname))
+        self.fields['itemvar'].choices = choices
+
+    def clean(self):
+        if self.cleaned_data.get('operation') == 'price' and not self.cleaned_data.get('price', '') != '':
+            raise ValidationError(_('You need to enter a price if you want to change the product price.'))

src/pretix/control/forms/vouchers.py

@@ -3,7 +3,6 @@ import copy
 from django import forms
 from django.core.exceptions import ValidationError
 from django.db.models import Q
-from django.forms import model_to_dict
 from django.utils.timezone import now
 from django.utils.translation import ugettext_lazy as _