check for invoice amounts after conversion

document.py

@@ -87,9 +87,41 @@ class Incoming(metaclass=PoolMeta):
                 # update invoice with imported data
                 if self.parsed_data:
                     invoice = self._readxml_update_invoice(invoice)
+                    invoice.save()
+                    self._readxml_check_invoice(invoice)
         # raise ValueError('stop')
         return invoice
 
+    def _readxml_check_invoice(self, invoice):
+        """ check if calculated totals match with data from xml
+
+        Raises:
+            UserError: if calculated values dont match
+                with xml-values
+        """
+        totals = self.parsed_data.get('total', None)
+        if not totals:
+            raise UserError(gettext(
+                'msg_convert_error.msg_convert_error',
+                msg='no totals-section in xml-data'))
+
+        for xfield, inv_field in [
+                ('taxbase', 'untaxed_amount'),
+                ('taxtotal', 'tax_amount'),
+                ('grand', 'total_amount')]:
+            xml_val = totals.get('taxbase', Decimal('0.0'))
+            inv_val = getattr(invoice, inv_field)
+            if xml_val != inv_val:
+                raise UserError(gettext(
+                    'document_incoming_invoice_xml.msg_convert_error',
+                    msg=' '.join([
+                        inv_field + ' mismatch',
+                        'from-xml=' + Report.format_currency(
+                            xml_val, None, invoice.currency),
+                        'calculated=' + Report.format_currency(
+                            inv_val, None, invoice.currency)
+                    ])))
+
     def _readxml_xpath(self, tags):
         """ generate xpath