Send notification mails when re-authentication is needed

src/newsreader/news/collection/tasks.py

@@ -1,5 +1,7 @@
 from django.conf import settings
 from django.core.exceptions import ObjectDoesNotExist
+from django.core.mail import send_mail
+from django.utils.translation import ugettext as _
 
 import requests
 
@@ -107,7 +109,15 @@ class RedditTokenTask(app.Task):
             user.reddit_refresh_token = None
             user.save()
 
-            # TODO add notification mail
+            message = _(
+                "Your Reddit account credentials have expired. Re-authenticate in"
+                " the settings page to keep retrieving Reddit specific information"
+                " from your account."
+            )
+
+            send_mail(
+                "Reddit account needs re-authentication", message, None, [user.email]
+            )
             return
 
         response_data = response.json()

src/newsreader/news/collection/twitter.py

@@ -5,8 +5,10 @@ from datetime import datetime
 from json import JSONDecodeError
 
 from django.conf import settings
+from django.core.mail import send_mail
 from django.utils import timezone
 from django.utils.html import format_html, urlize
+from django.utils.translation import ugettext as _
 
 import pytz
 
@@ -240,7 +242,18 @@ class TwitterClient(PostClient):
                     stream.rule.user.twitter_oauth_token_secret = None
                     stream.rule.user.save()
 
-                    # TODO add notification mail
+                    message = _(
+                        "Your Twitter account credentials have expired. Re-authenticate in"
+                        " the settings page to keep retrieving Twitter specific information"
+                        " from your account."
+                    )
+
+                    send_mail(
+                        "Twitter account needs re-authentication",
+                        message,
+                        None,
+                        [stream.rule.user.email],
+                    )
 
                     self.set_rule_error(stream.rule, e)