Updated API to handle pre-compiled pdfs

* added a method to letter/utils.py to get the PDF document from the S3
bucket
* added the logic to return the pdf or to produce a png of the pdf

app/letters/utils.py

@@ -1,5 +1,6 @@
 from datetime import datetime, timedelta
 
+import boto3
 from flask import current_app
 
 from notifications_utils.s3 import s3upload
@@ -10,6 +11,8 @@ from app.variables import Retention
 LETTERS_PDF_FILE_LOCATION_STRUCTURE = \
     '{folder}/NOTIFY.{reference}.{duplex}.{letter_class}.{colour}.{crown}.{date}.pdf'
 
+PRECOMPILED_BUCKET_PREFIX = '{folder}/NOTIFY.{reference}'
+
 
 def get_letter_pdf_filename(reference, crown):
     now = datetime.utcnow()
@@ -31,6 +34,15 @@ def get_letter_pdf_filename(reference, crown):
     return upload_file_name
 
 
+def get_bucket_prefix_for_notification(notification):
+    upload_file_name = PRECOMPILED_BUCKET_PREFIX.format(
+        folder=notification.created_at.date(),
+        reference=notification.reference
+    ).upper()
+
+    return upload_file_name
+
+
 def upload_letter_pdf(notification, pdf_data):
     current_app.logger.info("PDF Letter {} reference {} created at {}, {} bytes".format(
         notification.id, notification.reference, notification.created_at, len(pdf_data)))
@@ -48,3 +60,19 @@ def upload_letter_pdf(notification, pdf_data):
 
     current_app.logger.info("Uploaded letters PDF {} to {} for notification id {}".format(
         upload_file_name, current_app.config['LETTERS_PDF_BUCKET_NAME'], notification.id))
+
+
+def get_letter_pdf(notification):
+    bucket_name = current_app.config['LETTERS_PDF_BUCKET_NAME']
+
+    s3 = boto3.resource('s3')
+    bucket = s3.Bucket(bucket_name)
+
+    for item in bucket.objects.filter(Prefix=get_bucket_prefix_for_notification(notification)):
+        obj = s3.Object(
+            bucket_name=bucket_name,
+            key=item.key
+        )
+        file_content = obj.get()["Body"].read()
+
+    return file_content