re-add rss feeds

app/routes/topics.py

@@ -1,5 +1,6 @@
-from flask import Blueprint, redirect, url_for, render_template, request, session, abort
-
+from flask import Blueprint, redirect, url_for, render_template, request, session, abort, current_app
+from app import cache
+from ..lib.render_atom import render_atom_template
 from ..models import Topics, Threads, Subscriptions
 from ..auth import get_active_user
 import math
@@ -42,8 +43,20 @@ def topic(topic_id, slug):
             subscription = Subscriptions.find({'user_id': user.id, 'thread_id': thread['id']})
             if subscription:
                 subscriptions[thread['id']] = subscription.get_unread_count()
-    return render_template('topics/topic.html', topic=topic, threads=threads, sort_by=sort_by, page=page, page_count=page_count, subscriptions=subscriptions)
+    return render_template(
+        'topics/topic.html', topic=topic,
+        threads=threads, sort_by=sort_by,
+        page=page, page_count=page_count, subscriptions=subscriptions,
+        __feedlink=url_for('.feed', topic_id=topic_id, _external=True),
+        __feedtitle=f'latest threads in {topic.name}',
+    )
 
 @bp.get('/<int:topic_id>/feed.atom/')
+@cache.cached(timeout=5 * 60, unless=lambda: current_app.config['DEBUG'])
 def feed(topic_id):
-    return 'stub'
+    topic = Topics.find({'id': topic_id})
+    if not topic:
+        abort(404)
+
+    threads_list = topic.get_threads_with_op_rss()
+    return render_atom_template('topics/topic.atom', topic=topic, threads_list=threads_list)