add flag to return pdf content via api

this is only applicable when getting a single notification by id. it's
also ignored if the notification isn't a letter.

Otherwise, it overwrites the 'body' field in the response.

If the notification's pdf is available, it returns that, base64
encoded. If the pdf is not available, it returns an empty string.

The pdf won't be available if the notification's status is:
* pending-virus-scan
* virus-scan-failed
* validation-failed
* technical-failure

The pdf will be retrieved from the correct s3 bucket based on its type

tests/app/letters/test_letter_utils.py

@@ -80,6 +80,16 @@ def test_get_bucket_name_and_prefix_for_notification_precompiled_letter_using_te
         sample_precompiled_letter_notification_using_test_key.reference).upper()
 
 
+@freeze_time(FROZEN_DATE_TIME)
+def test_get_bucket_name_and_prefix_for_notification_templated_letter_using_test_key(sample_letter_notification):
+    sample_letter_notification.key_type = KEY_TYPE_TEST
+
+    bucket, bucket_prefix = get_bucket_name_and_prefix_for_notification(sample_letter_notification)
+
+    assert bucket == current_app.config['TEST_LETTERS_BUCKET_NAME']
+    assert bucket_prefix == 'NOTIFY.{}'.format(sample_letter_notification.reference).upper()
+
+
 @freeze_time(FROZEN_DATE_TIME)
 def test_get_bucket_name_and_prefix_for_failed_validation(sample_precompiled_letter_notification):
     sample_precompiled_letter_notification.status = NOTIFICATION_VALIDATION_FAILED

tests/app/v2/notifications/test_get_notifications.py

@@ -649,3 +649,38 @@ def test_get_notifications_renames_letter_statuses(client, sample_letter_templat
     json_response = json.loads(response.get_data(as_text=True))
     assert response.status_code == 200
     assert json_response['status'] == expected_status
+
+
+@pytest.mark.parametrize('status,expected_body,mock_called', [
+    ('created', 'Zm9v', True),
+    ('sending', 'Zm9v', True),
+    ('pending-virus-check', '', False),
+    ('virus-scan-failed', '', False),
+    ('validation-failed', '', False),
+    ('technical-failure', '', False),
+])
+def test_get_notification_only_returns_pdf_content_if_right_status(
+    client,
+    sample_letter_notification,
+    mocker,
+    status,
+    expected_body,
+    mock_called
+):
+    mock_get_letter_pdf = mocker.patch('app.v2.notifications.get_notifications.get_letter_pdf', return_value=b'foo')
+    sample_letter_notification.status = status
+
+    auth_header = create_authorization_header(service_id=sample_letter_notification.service_id)
+    response = client.get(
+        path=url_for(
+            'v2_notifications.get_notification_by_id',
+            notification_id=sample_letter_notification.id,
+            return_pdf_content='true'
+        ),
+        headers=[('Content-Type', 'application/json'), auth_header]
+    )
+
+    json_response = json.loads(response.get_data(as_text=True))
+    assert response.status_code == 200
+    assert json_response['body'] == expected_body
+    assert mock_get_letter_pdf.called == mock_called