erp5_free_subscription: several improvements on interaction the updated Free Subscription

from Free Subscription Request:

- In case of 'subscription', do not create a new Free Subscription
if one already exists
- In case of 'unsubscription' still create a Free Subscription if none exists
and invalidate it at once
- Allow having variation_category that will be passed to the Free Subscription
- Handle definition of effective_date and expiration_date in Free Subscription better, Rule is:
We prioritise effective_date (or expiration_date) if it exists
Then getStopDate result (stop_date or acquiring from start_date) if it is not None
Finally current date
- Have assertions on variation_category and raise in case of unknown type

bt5/erp5_free_subscription/WorkflowTemplateItem/portal_workflow/free_subscription_interaction_workflow/scripts/Request_updateFreeSubscription.py

 request = state_change["object"]
+portal = request.getPortalObject()
+now = DateTime()
+request_type = request.getFreeSubscriptionRequestType()
+resource = request.getResource()
+stop_date = request.getStopDate()
 
-if request.getFreeSubscriptionRequestType() == "unsubscription":
-  free_subscription = request.getFollowUpValue()
-  if free_subscription.getValidationState() != "invalidated":
-    free_subscription.invalidate()
-elif request.getFreeSubscriptionRequestType() == "subscription":
-  from DateTime import DateTime
-  portal = request.getPortalObject()
+# Rule is we prioritise effective_date if it exists,
+# then getStopDate result (stop_date or acquiring from start_date) if it is not None
+# and finally current date
+if request.hasEffectiveDate():
+  effective_date = request.getEffectiveDate()
+else:
+  effective_date = stop_date or now
+
+free_subscription = request.getFollowUpValue()
+if free_subscription is None:
   free_subscription = portal.free_subscription_module.newContent(
     source=request.getSource(),
     destination=request.getDestination(),
-    resource=request.getResource(),
-    effective_date=DateTime())
-  free_subscription.validate()
-  request.setFollowUpValue(free_subscription)
+    resource=resource,
+    effective_date=effective_date,
+  )
+request.setFollowUpValue(free_subscription)
+variation_category_list = request.getVariationCategoryList()
+
+if request_type == "unsubscription":
+  assert not variation_category_list, 'unsubscription type of Free Subscription Request with non empty variation_category_list'
+  validation_state = free_subscription.getValidationState()
+  if validation_state != "invalidated":
+    if validation_state == "draft":
+      # validate, so that we can invalidate in same transaction
+      free_subscription.validate()
+    # Rule is we prioritise expiration_date if it exists
+    # then getStopDate result (stop_date or acquiring from start_date) if it is not None
+    # and finally current date
+    if request.hasExpirationDate():
+      expiration_date = request.getExpirationDate()
+    else:
+      expiration_date = stop_date or now
+    free_subscription.setExpirationDate(expiration_date)
+    free_subscription.invalidate()
+elif request_type == "subscription":
+  variation_range_category_list = request.getVariationRangeCategoryList()
+  if not variation_category_list:
+    assert not request.getVariationRangeCategoryList(), 'subscription type of Free Subscription Request with non empty variation_category_list, while resource has list defined'
+  for variation_category in variation_category_list:
+    assert variation_category in variation_range_category_list, 'not allowed variation_category %s' % variation_category
+  free_subscription.setExpirationDate(None)
+  if free_subscription.getValidationState() != "validated":
+    free_subscription.validate()
+    free_subscription.setEffectiveDate(effective_date)
+else:
+  raise RuntimeError('Unknown request type %s' % request_type)
+
+free_subscription.setVariationCategoryList(variation_category_list)