API: Allow to add a fee to an order (#4806) (#4829)

* API: Allow to add a fee to an order (#4806)

* Fix example in docs

* Consistent order of examples

* Add create_fees to example

* docs: None -> null

* docs: update fee_type options

---------

Co-authored-by: Mira Weller <weller@rami.io>

src/pretix/api/serializers/orderchange.py

@@ -30,7 +30,7 @@ from rest_framework.exceptions import ValidationError
 
 from pretix.api.serializers.order import (
     AnswerCreateSerializer, AnswerSerializer, CompatibleCountryField,
-    OrderPositionCreateSerializer,
+    OrderFeeCreateSerializer, OrderPositionCreateSerializer,
 )
 from pretix.base.models import ItemVariation, Order, OrderFee, OrderPosition
 from pretix.base.services.orders import OrderError
@@ -104,6 +104,54 @@ class OrderPositionCreateForExistingOrderSerializer(OrderPositionCreateSerialize
             raise ValidationError(str(e))
 
 
+class OrderFeeCreateForExistingOrderSerializer(OrderFeeCreateSerializer):
+    order = serializers.SlugRelatedField(slug_field='code', queryset=Order.objects.none(), required=True, allow_null=False)
+    value = serializers.DecimalField(required=True, allow_null=False, decimal_places=2,
+                                     max_digits=13)
+    internal_type = serializers.CharField(required=False, default="")
+
+    class Meta:
+        model = OrderFee
+        fields = ('order', 'fee_type', 'value', 'description', 'internal_type', 'tax_rule')
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        if not self.context:
+            return
+        self.fields['order'].queryset = self.context['event'].orders.all()
+        self.fields['tax_rule'].queryset = self.context['event'].tax_rules.all()
+        if 'order' in self.context:
+            del self.fields['order']
+
+    def validate(self, data):
+        data = super().validate(data)
+        if 'order' in self.context:
+            data['order'] = self.context['order']
+        return data
+
+    def create(self, validated_data):
+        ocm = self.context['ocm']
+
+        try:
+            f = OrderFee(
+                order=validated_data['order'],
+                fee_type=validated_data['fee_type'],
+                value=validated_data.get('value'),
+                description=validated_data.get('description'),
+                internal_type=validated_data.get('internal_type'),
+                tax_rule=validated_data.get('tax_rule'),
+            )
+            f._calculate_tax()
+            ocm.add_fee(f)
+            if self.context.get('commit', True):
+                ocm.commit()
+                return validated_data['order'].fees.order_by('-pk').first()
+            else:
+                return OrderFee()  # fake to appease DRF
+        except OrderError as e:
+            raise ValidationError(str(e))
+
+
 class OrderPositionInfoPatchSerializer(serializers.ModelSerializer):
     answers = AnswerSerializer(many=True)
     country = CompatibleCountryField(source='*')
@@ -401,6 +449,9 @@ class OrderChangeOperationSerializer(serializers.Serializer):
         self.fields['split_positions'] = SelectPositionSerializer(
             many=True, required=False, context=self.context
         )
+        self.fields['create_fees'] = OrderFeeCreateForExistingOrderSerializer(
+            many=True, required=False, context=self.context
+        )
         self.fields['patch_fees'] = PatchFeeSerializer(
             many=True, required=False, context=self.context
         )