add unread count to topnav and update subscription on thread view

app/models.py

@@ -117,6 +117,24 @@ class Users(Model):
     def is_subscribed(self, thread_id):
         return Subscriptions.count({'user_id': self.id, 'thread_id': thread_id}) > 0
 
+    def get_unread_count(self):
+        q = """
+            SELECT
+                COUNT(posts.id) as c
+            FROM
+                subscriptions
+            JOIN
+                threads ON subscriptions.thread_id = threads.id
+            JOIN
+                posts ON threads.id = posts.thread_id
+            WHERE
+                subscriptions.user_id = ?
+            AND
+                posts.created_at > subscriptions.last_seen
+        """
+        res = db.fetch_one(q, self.id)
+        return res["c"] or 0
+
 
 class Topics(Model):
     table = 'topics'