Upload pre-compiled letter PDF to S3

Pre-compiled letter endpoint uploads PDF contents to S3 directly
instead of creating a letter task to generate PDF using template
preview.

This moves some of the utility functions used by existing letter
celery tasks to app.letters.utils, so that they can be reused by
the API endpoint.

app/celery/letters_pdf_tasks.py

@@ -1,4 +1,3 @@
-from datetime import datetime, timedelta
 import math
 
 from flask import current_app
@@ -9,43 +8,18 @@ from requests import (
 )
 from botocore.exceptions import ClientError as BotoClientError
 
-from notifications_utils.s3 import s3upload
-
 from app import notify_celery
 from app.aws import s3
 from app.config import QueueNames, TaskNames
-from app.variables import Retention
 from app.dao.notifications_dao import (
     get_notification_by_id,
     update_notification_status_by_id,
     dao_update_notification,
     dao_get_notifications_by_references,
 )
+from app.letters.utils import upload_letter_pdf
 from app.models import NOTIFICATION_CREATED
 
-LETTERS_PDF_FILE_LOCATION_STRUCTURE = \
-    '{folder}/NOTIFY.{reference}.{duplex}.{letter_class}.{colour}.{crown}.{date}.pdf'
-
-
-def get_letter_pdf_filename(reference, crown):
-    now = datetime.utcnow()
-
-    print_datetime = now
-    if now.time() > current_app.config.get('LETTER_PROCESSING_DEADLINE'):
-        print_datetime = now + timedelta(days=1)
-
-    upload_file_name = LETTERS_PDF_FILE_LOCATION_STRUCTURE.format(
-        folder=print_datetime.date(),
-        reference=reference,
-        duplex="D",
-        letter_class="2",
-        colour="C",
-        crown="C" if crown else "N",
-        date=now.strftime('%Y%m%d%H%M%S')
-    ).upper()
-
-    return upload_file_name
-
 
 @notify_celery.task(bind=True, name="create-letters-pdf", max_retries=15, default_retry_delay=300)
 @statsd(namespace="tasks")
@@ -59,22 +33,8 @@ def create_letters_pdf(self, notification_id):
             org_id=notification.service.dvla_organisation.id,
             values=notification.personalisation
         )
-        current_app.logger.info("PDF Letter {} reference {} created at {}, {} bytes".format(
-            notification.id, notification.reference, notification.created_at, len(pdf_data)))
 
-        upload_file_name = get_letter_pdf_filename(
-            notification.reference, notification.service.crown)
-
-        s3upload(
-            filedata=pdf_data,
-            region=current_app.config['AWS_REGION'],
-            bucket_name=current_app.config['LETTERS_PDF_BUCKET_NAME'],
-            file_location=upload_file_name,
-            tags={Retention.KEY: Retention.ONE_WEEK}
-        )
-
-        current_app.logger.info("Uploaded letters PDF {} to {}".format(
-            upload_file_name, current_app.config['LETTERS_PDF_BUCKET_NAME']))
+        upload_letter_pdf(notification, pdf_data)
 
         notification.billable_units = billable_units
         dao_update_notification(notification)