How to move failed testcase code from @Aftermethod to TESTNG Listener?

Question

This is the working code to capture screenshot for failure testcases in Extent reports I am trying to put inside TESTNG listeners:

@AfterMethod
public void tearDown(ItestResult result){

    if(result.getStatus()==ItestResult.FAILURE){
        extentTest.log(LogStatus.FAIL,"TEST CASE FAILED IS "+result.getName());
        extentTest.log(LogStatus.FAIL, "TEST CASE FAILED IS "+result.getThrowable();

        String screenshotPath = FreeCRMTest.getScreenshot(driver, result.getName());
        extentTest.log(LogStatus.FAIL, extentTest.addScreeCapture(screenshotPath));
    }
}

This is code to capture screenshot which I placed in base class:

    public class base{
        public WebDriver driver;
        public WebDriver initializeDriver()
        {
            Properties prop=new Properties();
            FileInputStream fis=new FileInputStream("path of data.properties");
            prop.load(fis);
            String browserName=prop.getProperty("browser");
            if(browserName.equals("chrome"))
            {
                System.setProperty("webdriver.chrome.driver", "E:\Selenium Grid\chromedriver.exe");
                driver=new ChromeDriver();
            }

            else if (browserName.equals("firefox"))
            {
                System.setProperty("webdriver.gecko.driver", "E:\Selenium Grid\ geckodriver.exe");
                driver=new FirefoxDriver();
            }

            driver.manage().timeouts().implicitlyWait(Duration.ofSeconds(20));
            return driver;
        }
    }


    public static String getScreenshot(WebDriver driver, String screenshotName) throw IOException{
        String dateName = new SimpleDateFormat("yyyyMMddhhmmss").fomat(new Date());
        TakesScreenshot ts = (TakesScreenshot)driver;
        File source=ts.getScreenshotAs(OutputType.File);
        String destination=System.getProperty("user.dir")+"/FailedTestsScreenshots/" + screenshotName+dateName+ ".png";
        File finalDestination = new File(destination);
        FileUtils.copyFile(source, Final Destination);
        return destination;
    }

This is how I moving my code from @Aftermethod to TESTNG listener but it's throwing driver is null:

        ExtentTest test;
        public void onTestFailure(ItestFailure) {
        test.log(STATUS.FAIL, result.getThrowable());

    try{
            String screenshotPath;
            screenshotPath=getScreenshot(driver, result.getName());
            test.log(STATUS.FAIL, test.addScreenCapture(screenshotPath));
        }catch(IOException e) {
            e.printStackTrace();
        }
    }

This is the maintest case which calls OnTestFailure:

    public class Homepage extends Resources.base{
        @Test
        public void basePageNavigation()
        {
            driver=initializeDriver();
            driver.get("http://www.google.com");
            Assert.assertTrue("Google1", driver.gettitle() );
        }
    }