impl Agent {
    /// BlueZ capability parameter.
    pub(crate) fn capability(&self) -> &'static str {
        let keyboard = self.request_passkey.is_some() || self.request_pin_code.is_some();
        let display_only = self.display_passkey.is_some() || self.display_pin_code.is_some();
        let yes_no = self.request_confirmation.is_some()
            || self.request_authorization.is_some()
            || self.authorize_service.is_some();

        match (keyboard, display_only, yes_no) {
            (true, false, false) => "KeyboardOnly",
            (false, true, false) => "DisplayOnly",
            (false, _, true) => "DisplayYesNo",
            (true, true, _) | (true, _, true) => "KeyboardDisplay",
            (false, false, false) => "NoInputNoOutput",
        }
    }
}