Create new task to build dvla file.

This will transform each notification in a job to a row in a file.
The file is then uploaded to S3.
The files will later be aggregated by the notifications-ftp app to send to dvla.

The method to upload the file to S3 should be pulled into notifications-utils package.
It is the same method used in notifications-admin.

app/celery/tasks.py

@@ -1,10 +1,12 @@
+import botocore
+from boto3 import resource
 from datetime import (datetime)
 
 from flask import current_app
 from notifications_utils.recipients import (
     RecipientCSV
 )
-from notifications_utils.template import SMSMessageTemplate, WithSubjectTemplate
+from notifications_utils.template import SMSMessageTemplate, WithSubjectTemplate, LetterDVLATemplate
 from sqlalchemy.exc import SQLAlchemyError
 from app import (
     create_uuid,
@@ -16,8 +18,9 @@ from app.aws import s3
 from app.celery import provider_tasks
 from app.dao.jobs_dao import (
     dao_update_job,
-    dao_get_job_by_id
-)
+    dao_get_job_by_id,
+    all_notifications_are_created_for_job,
+    dao_get_all_notifications_for_job)
 from app.dao.notifications_dao import get_notification_by_id
 from app.dao.services_dao import dao_fetch_service_by_id, fetch_todays_total_message_count
 from app.dao.templates_dao import dao_get_template_by_id
@@ -76,6 +79,8 @@ def process_job(job_id):
     current_app.logger.info(
         "Job {} created at {} started at {} finished at {}".format(job_id, job.created_at, start, finished)
     )
+    if template.template_type == LETTER_TYPE:
+        build_dvla_file.apply_async([str(job.id)], queue='process-job')
 
 
 def process_row(row_number, recipient, personalisation, template, job, service):
@@ -248,13 +253,61 @@ def persist_letter(
             notification_id=notification_id
         )
 
-        # TODO: deliver letters
-
         current_app.logger.info("Letter {} created at {}".format(saved_notification.id, created_at))
     except SQLAlchemyError as e:
         handle_exception(self, notification, notification_id, e)
 
 
+@notify_celery.task(bind=True, name="build-dvla-file", max_retries=5, default_retry_delay=300)
+@statsd(namespace="tasks")
+def build_dvla_file(self, job_id):
+    if all_notifications_are_created_for_job(job_id):
+        notifications = dao_get_all_notifications_for_job(job_id)
+        file = ""
+        for n in notifications:
+            t = {"content": n.template.content, "subject": n.template.subject}
+            template = LetterDVLATemplate(t, n.personalisation, 1)
+            # print(str(template))
+            file = file + str(template) + "\n"
+        s3upload(filedata=file,
+                 region=current_app.config['AWS_REGION'],
+                 bucket_name=current_app.config['DVLA_UPLOAD_BUCKET_NAME'],
+                 file_location="{}-dvla-job.text".format(job_id))
+    else:
+        self.retry(queue="retry", exc="All notifications for job {} are not persisted".format(job_id))
+
+
+def s3upload(filedata, region, bucket_name, file_location):
+    # TODO: move this method to utils. Will need to change the filedata from here to send contents in filedata['data']
+    _s3 = resource('s3')
+    # contents = filedata['data']
+    contents = filedata
+
+    exists = True
+    try:
+        _s3.meta.client.head_bucket(
+            Bucket=bucket_name)
+    except botocore.exceptions.ClientError as e:
+        error_code = int(e.response['Error']['Code'])
+        if error_code == 404:
+            exists = False
+        else:
+            current_app.logger.error(
+                "Unable to create s3 bucket {}".format(bucket_name))
+            raise e
+
+    if not exists:
+        _s3.create_bucket(Bucket=bucket_name,
+                          CreateBucketConfiguration={'LocationConstraint': region})
+
+    upload_id = create_uuid()
+    upload_file_name = file_location
+    key = _s3.Object(bucket_name, upload_file_name)
+    key.put(Body=contents, ServerSideEncryption='AES256')
+
+    return upload_id
+
+
 def handle_exception(task, notification, notification_id, exc):
     if not get_notification_by_id(notification_id):
         retry_msg = '{task} notification for job {job} row number {row} and notification id {noti}'.format(