Pluggable invoice transmission methods (#5020)

* Flexible invoice transmission

* UI work

* Add peppol and output

* API support

* Profile integration

* Simplify form for individuals

* Remove sent_to_customer usage

* more steps

* Revert "Bank transfer: Allow to send the invoice direclty to the accounting department (#2975)"

This reverts commit cea6c340be.

* minor fixes

* Fixes after rebase

* update stati

* Backend view

* Transmit and show status

* status, retransmission

* API retransmission

* More fields

* API docs

* Plugin docs

* Update migration

* Add missing license headers

* Remove dead code, fix current tests

* Run isort

* Update regex

* Rebase migration

* Fix migration

* Add tests, fix bugs

* Rebase migration

* Apply suggestion from @luelista

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

* Apply suggestion from @luelista

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

* Apply suggestion from @luelista

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

* Apply suggestion from @luelista

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

* Apply suggestion from @luelista

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

* Make migration reversible

* Add TransmissionType.enforce_transmission

* Fix registries API usage after rebase

* Remove code I forgot to delete

* Update transmission status display depending on type

* Add testmode_supported

* Update src/pretix/static/pretixbase/js/addressform.js

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

* Update src/pretix/static/pretixbase/js/addressform.js

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

* Update src/pretix/static/pretixbase/js/addressform.js

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

* New mechanism for non-required invoice forms

* Update src/pretix/base/invoicing/transmission.py

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

* Declare testmode_supported for email

* Make transmission_email_other an implementation detail

* Fix failing tests and add new ones

* Update src/pretix/base/services/invoices.py

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

* Add emails to email history

* Fix comma error

* More generic default email text

* Cleanup

* Remove "email invoices" button and refine logic

* Rebase migration

* Fix edge case

---------

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

src/pretix/api/views/order.py

@@ -88,7 +88,7 @@ from pretix.base.secrets import assign_ticket_secret
 from pretix.base.services import tickets
 from pretix.base.services.invoices import (
     generate_cancellation, generate_invoice, invoice_pdf, invoice_qualified,
-    regenerate_invoice,
+    regenerate_invoice, transmit_invoice,
 )
 from pretix.base.services.mail import SendMailException
 from pretix.base.services.orders import (
@@ -1891,6 +1891,12 @@ class RetryException(APIException):
     default_code = 'retry_later'
 
 
+class CurrentlyInflightException(APIException):
+    status_code = 409
+    default_detail = 'The requested action is already in progress.'
+    default_code = 'currently_inflight'
+
+
 class InvoiceViewSet(viewsets.ReadOnlyModelViewSet):
     serializer_class = InvoiceSerializer
     queryset = Invoice.objects.none()
@@ -1939,13 +1945,52 @@ class InvoiceViewSet(viewsets.ReadOnlyModelViewSet):
         resp['Content-Disposition'] = 'attachment; filename="{}.pdf"'.format(invoice.number)
         return resp
 
+    @action(detail=True, methods=['POST'])
+    def transmit(self, request, **kwargs):
+        invoice = self.get_object()
+        if invoice.shredded:
+            raise PermissionDenied('The invoice file is no longer stored on the server.')
+
+        if invoice.transmission_status != Invoice.TRANSMISSION_STATUS_PENDING:
+            raise PermissionDenied('The invoice is not in pending state.')
+
+        transmit_invoice.apply_async(args=(self.request.event.pk, invoice.pk, False))
+        return Response(status=204)
+
+    @action(detail=True, methods=['POST'])
+    def retransmit(self, request, **kwargs):
+        invoice = self.get_object()
+        if invoice.shredded:
+            raise PermissionDenied('The invoice file is no longer stored on the server.')
+
+        with transaction.atomic(durable=True):
+            invoice = Invoice.objects.select_for_update(of=OF_SELF).get(pk=invoice.pk)
+
+            if invoice.transmission_status == Invoice.TRANSMISSION_STATUS_INFLIGHT:
+                raise CurrentlyInflightException()
+
+            invoice.transmission_status = Invoice.TRANSMISSION_STATUS_PENDING
+            invoice.transmission_date = now()
+            invoice.save(update_fields=["transmission_status", "transmission_date"])
+            invoice.order.log_action(
+                'pretix.event.order.invoice.retransmitted',
+                user=self.request.user,
+                auth=self.request.auth,
+                data={
+                    'invoice': invoice.pk,
+                    'full_invoice_no': invoice.full_invoice_no,
+                }
+            )
+        transmit_invoice.apply_async(args=(self.request.event.pk, invoice.pk, True))
+        return Response(status=204)
+
     @action(detail=True, methods=['POST'])
     def regenerate(self, request, **kwargs):
         inv = self.get_object()
         if inv.canceled:
             raise ValidationError('The invoice has already been canceled.')
-        if not inv.event.settings.invoice_regenerate_allowed:
-            raise PermissionDenied('Invoices may not be changed after they are created.')
+        if not inv.regenerate_allowed:
+            raise PermissionDenied('Invoice may not be regenerated.')
         elif inv.shredded:
             raise PermissionDenied('The invoice file is no longer stored on the server.')
         elif inv.sent_to_organizer: