Search for emails or texts, depending on term

The caseworking view is going to have a page which displays emails and
text messages combined together.

In order for the search to work on this page the user needs to be able
to search for an email or a text message. This commit makes it guess
what to search for when the `notification_type` isn’t known (basically
by saying ‘if the search term is only digits they’re probably looking
searching by phone number’).

app/dao/notifications_dao.py

@@ -1,4 +1,5 @@
 import functools
+import string
 from datetime import (
     datetime,
     timedelta,
@@ -425,7 +426,10 @@ def dao_update_notifications_by_reference(references, update_dict):
 
 
 @statsd(namespace="dao")
-def dao_get_notifications_by_to_field(service_id, search_term, notification_type, statuses=None):
+def dao_get_notifications_by_to_field(service_id, search_term, notification_type=None, statuses=None):
+
+    if notification_type is None:
+        notification_type = guess_notification_type(search_term)
 
     if notification_type == SMS_TYPE:
         normalised = try_validate_and_format_phone_number(search_term)
@@ -440,6 +444,7 @@ def dao_get_notifications_by_to_field(service_id, search_term, notification_type
             normalised = validate_and_format_email_address(search_term)
         except InvalidEmailError:
             normalised = search_term.lower()
+
     else:
         raise InvalidRequest("Only email and SMS can use search by recipient", 400)
 
@@ -597,3 +602,10 @@ def notifications_not_yet_sent(should_be_sending_after_seconds, notification_typ
         Notification.status == NOTIFICATION_CREATED
     ).all()
     return notifications
+
+
+def guess_notification_type(search_term):
+    if set(search_term) & set(string.ascii_letters + '@'):
+        return EMAIL_TYPE
+    else:
+        return SMS_TYPE