Add endpoint for getting / creating a hidden template

We want a way of getting the hidden precompiled template from admin,
so this adds an endpoint which gets the template or creates it if it doesn't
exist. The function to get or create the hidden template already existed
but has been moved to the template DAO now that it is used in more
places.

app/dao/templates_dao.py

@@ -1,10 +1,13 @@
 from datetime import datetime
 import uuid
 
+from flask import current_app
 from sqlalchemy import asc, desc
 
 from app import db
 from app.models import (
+    LETTER_TYPE,
+    SECOND_CLASS,
     Template,
     TemplateHistory,
     TemplateRedacted
@@ -14,6 +17,7 @@ from app.dao.dao_utils import (
     version_class,
     VersionOptions,
 )
+from app.dao.users_dao import get_user_by_id
 
 
 @transactional
@@ -135,3 +139,28 @@ def dao_get_template_versions(service_id, template_id):
     ).order_by(
         desc(TemplateHistory.version)
     ).all()
+
+
+def get_precompiled_letter_template(service_id):
+    template = Template.query.filter_by(
+        service_id=service_id,
+        template_type=LETTER_TYPE,
+        hidden=True
+    ).first()
+    if template is not None:
+        return template
+
+    template = Template(
+        name='Pre-compiled PDF',
+        created_by=get_user_by_id(current_app.config['NOTIFY_USER_ID']),
+        service_id=service_id,
+        template_type=LETTER_TYPE,
+        hidden=True,
+        subject='Pre-compiled PDF',
+        content='',
+        postage=SECOND_CLASS
+    )
+
+    dao_create_template(template)
+
+    return template