def _get_screenshots(self) -> list[bytes]:
    """
    Get chart or dashboard screenshots
    :raises: ReportScheduleScreenshotFailedError
    """
    url = self._get_url()
    _, username = get_executor(
        executor_types=app.config["ALERT_REPORTS_EXECUTE_AS"],
        model=self._report_schedule,
    )
    user = security_manager.find_user(username)
    if self._report_schedule.chart:
        window_width, window_height = app.config["WEBDRIVER_WINDOW"]["slice"]
        window_size = (
            self._report_schedule.custom_width or window_width,
            self._report_schedule.custom_height or window_height,
        )
        screenshot: Union[ChartScreenshot, DashboardScreenshot] = ChartScreenshot(
            url,
            self._report_schedule.chart.digest,
            window_size=window_size,
            thumb_size=app.config["WEBDRIVER_WINDOW"]["slice"],
        )
    else:
        window_width, window_height = app.config["WEBDRIVER_WINDOW"]["dashboard"]
        window_size = (
            self._report_schedule.custom_width or window_width,
            self._report_schedule.custom_height or window_height,
        )
        screenshot = DashboardScreenshot(
            url,
            self._report_schedule.dashboard.digest,
            window_size=window_size,
            thumb_size=app.config["WEBDRIVER_WINDOW"]["dashboard"],
        )
    try:
        image = screenshot.get_screenshot(user=user)
    except SoftTimeLimitExceeded as ex:
        logger.warning("A timeout occurred while taking a screenshot.")
        raise ReportScheduleScreenshotTimeout() from ex
    except Exception as ex:
        raise ReportScheduleScreenshotFailedError(
            f"Failed taking a screenshot {str(ex)}"
        ) from ex
    if not image:
        raise ReportScheduleScreenshotFailedError()
    return [image]

def _get_pdf(self) -> bytes:
    """
    Get chart or dashboard pdf
    :raises: ReportSchedulePdfFailedError
    """
    screenshots = self._get_screenshots()
    pdf = build_pdf_from_screenshots(screenshots)

    return pdf