make sure form doesn't make it possible to post to locked topic

app/models.py

@@ -71,6 +71,18 @@ class Users(Model):
                 subscriptions.user_id = ?"""
         return db.query(q, self.id)
 
+    def can_post_to_topic(self, topic):
+        if self.is_guest():
+            return False
+
+        if self.is_mod():
+            return True
+
+        if topic['is_locked']:
+            return False
+
+        return True
+
 
 class Topics(Model):
     table = "topics"

app/templates/threads/create.html

@@ -8,7 +8,8 @@
     <label for="topic_id">Topic</label>
     <select name="topic_id" id="topic_id" autocomplete="off">
       {% for topic in all_topics %}
-        <option value="{{ topic['id'] }}" {{"selected" if (request.args.get('topic_id')) == (topic['id'] | string) else ""}}>{{ topic['name'] }}</option>
+        {% set disable_topic = active_user and not active_user.can_post_to_topic(topic) %}
+        <option value="{{ topic['id'] }}" {{"selected" if (request.args.get('topic_id')) == (topic['id'] | string) else ""}} {{'disabled' if disable_topic else ''}} >{{ topic['name'] }}{{ ' (locked)' if topic.is_locked }}</option>
       {% endfor %}
     </select><br>
     <label for="title">Thread title</label>