public function getPermissions($user_id = null)
    {
        static $permissions = array();

        if (!isset($user_id)) {
            $user_id = $this->uid;
        }

        if (isset($permissions[$user_id])) {
            return $permissions[$user_id];
        }

        $user = $this->get($user_id);

        if (empty($user['role_id'])) {
            return $permissions[$user_id] = array();
        }

        $role = array();
        if (isset($user['role_permissions'])) {
            $role['permissions'] = $user['role_permissions'];
        } else {
            $role = $this->role->get($user['role_id']);
        }

        if (empty($role['permissions'])) {
            return $permissions[$user_id] = array();
        }

        return $permissions[$user_id] = (array) $role['permissions'];
    }