Fill in root_status_id and add to parent's reply list, handle unable to fetch parent (this should be a stub)

src/model/status.c

@@ -182,8 +182,23 @@ bool status_sync_from_activity_pub( struct status* s, struct ap_activity* act )
 
 	if( act->in_reply_to ) {
 		struct status* parent = status_from_uri_or_fetch( act->in_reply_to );
-		s->in_reply_to = parent->id;
-		status_free(parent);
+		if( parent ) {
+			s->in_reply_to = parent->id;
+			s->root_status_id = parent->root_status_id;
+
+			bool is_already_parent_reply = false;
+			for( int i = 0; i < parent->replies.count; ++i ) {
+				if( parent->replies.items[i] == s->id ) {
+					is_already_parent_reply = true;
+				}
+			}
+			if( !is_already_parent_reply ) {
+				int id = s->id;
+				array_append( &parent->replies, sizeof(id), &id );
+				status_save(parent);
+			}
+			status_free(parent);
+		}
 	}
 	for( int i = 0; i < act->tags.count; ++i ) {
 		struct ap_activity_tag* tag = act->tags.items[i];