only send letters in created state to ftp app for zipping

this means if we end up with some notifications sending and others not,
due to problems with the ftp connectivity for example, we don't re-send
those that worked.

As a reminder, letter pdf notifications start as created and stay that
way until we have sent the zip file to DVLA, at which point they are
updated to sending
 #

app/celery/letters_pdf_tasks.py

@@ -13,8 +13,10 @@ from app.config import QueueNames, TaskNames
 from app.dao.notifications_dao import (
     get_notification_by_id,
     update_notification_status_by_id,
-    dao_update_notification
+    dao_update_notification,
+    dao_get_notifications_by_references,
 )
+from app.models import NOTIFICATION_CREATED
 from app.statsd_decorators import statsd
 
 
@@ -112,7 +114,7 @@ def group_letters(letter_pdfs):
     running_filesize = 0
     list_of_files = []
     for letter in letter_pdfs:
-        if letter['Key'].lower().endswith('.pdf'):
+        if letter['Key'].lower().endswith('.pdf') and letter_in_created_state(letter['Key']):
             if (
                 running_filesize + letter['Size'] > current_app.config['MAX_LETTER_PDF_ZIP_FILESIZE'] or
                 len(list_of_files) >= current_app.config['MAX_LETTER_PDF_COUNT_PER_ZIP']
@@ -126,3 +128,19 @@ def group_letters(letter_pdfs):
 
     if list_of_files:
         yield list_of_files
+
+
+def letter_in_created_state(filename):
+    # filename looks like '2018-01-13/NOTIFY.ABCDEF1234567890.D.2.C.C.20180113120000.PDF'
+    subfolder = filename.split('/')[0]
+    ref = filename.split('.')[1]
+    notifications = dao_get_notifications_by_references([ref])
+    if notifications:
+        if notifications[0].status == NOTIFICATION_CREATED:
+            return True
+        current_app.logger.info('Collating letters for {} but notification with reference {} already in {}'.format(
+            subfolder,
+            ref,
+            notifications[0].status
+        ))
+    return False