/**
  * Default constructor
  */
 public function __construct($plugin)
 {
     parent::__construct($plugin);
     $this->rc = $plugin->rc;
     $this->plugin = $plugin;
     // read database config
     $db = $this->rc->get_dbh();
     $this->db_lists = $this->rc->config->get('db_table_lists', $db->table_name($this->db_lists));
     $this->db_lists_caldav_props = $this->rc->config->get('db_table_lists_caldav_props', $db->table_name($this->db_lists_caldav_props));
     $this->db_tasks = $this->rc->config->get('db_table_tasks', $db->table_name($this->db_tasks));
     $this->db_tasks_caldav_props = $this->rc->config->get('db_table_tasks_caldav_props', $db->table_name($this->db_tasks_caldav_props));
     $this->crypt_key = $this->rc->config->get("calendar_crypt_key", "%E`c{2;<J2F^4_&._BxfQ<5Pf3qv!m{e");
     $this->_init_sync_clients();
 }