If client reference not given, try to get it from personalisation.

This is mostly useful for letters.

For templated letters sent via interface, whether one-offs
or CSV uploads, we do not give our users a way to set client reference.

Still, they often have a placeholder with reference that we could use
to set client_reference field.

Why is this helpful?

When letter is returned, or when we experience some printing issues,
often it is difficult to identify letters after the retention period.

This change will make it easier for some users to identify letters.
It will have more impact if we inform our users of this in template
editing guidance.

tests/app/notifications/test_process_notification.py

@@ -96,6 +96,42 @@ def test_persist_notification_creates_and_save_to_db(sample_template, sample_api
     assert notification_from_db.reply_to_text == sample_template.service.get_default_sms_sender()
 
 
+@pytest.mark.parametrize('client_reference,personalisation,expected_client_reference', [
+    ('clientref1', {}, 'clientref1'),
+    ('clientref1', {'reference': 'ref2'}, 'clientref1'),
+    (None, {'reference': 'ref2'}, 'ref2'),
+    (None, {'foo': 'bar'}, None),
+])
+def test_persist_notification_sets_client_reference_correctly(
+    sample_letter_template, sample_api_key, client_reference, personalisation, expected_client_reference
+):
+
+    assert Notification.query.count() == 0
+    assert NotificationHistory.query.count() == 0
+    notification = persist_notification(
+        template_id=sample_letter_template.id,
+        template_version=sample_letter_template.version,
+        recipient='3 Somerset House',
+        service=sample_letter_template.service,
+        personalisation=personalisation,
+        notification_type='letter',
+        api_key_id=sample_api_key.id,
+        key_type=sample_api_key.key_type,
+        reference="ref",
+        client_reference=client_reference,
+    )
+
+    assert Notification.query.get(notification.id) is not None
+
+    notification_from_db = Notification.query.one()
+
+    assert notification_from_db.id == notification.id
+    assert notification_from_db.template_id == notification.template_id
+    assert notification_from_db.notification_type == notification.notification_type
+    assert notification_from_db.reference == notification.reference
+    assert notification_from_db.client_reference == expected_client_reference
+
+
 def test_persist_notification_throws_exception_when_missing_template(sample_api_key):
     assert Notification.query.count() == 0
     assert NotificationHistory.query.count() == 0