/******************************************************************************
 * This program masks all but the last four digits if a credit card number.
 * 
 * Copyright © 2021 Richard Lesh.  All rights reserved.
 *****************************************************************************/

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.regex.Pattern;
import org.pureprogrammer.Utils;

public class CreditCardMask {

    static final List<String> TEST_CASES = Utils.listFromStrings(new String[]{"1234 5678 9012 3456", "4893 8573 0203 1929", "6992 2839 4929 3902"});

    static String maskCreditCard(String cardNumber) {
        return Pattern.compile("\\d{4,4} ").matcher(cardNumber).replaceAll("XXXX ");
    }

    public static void main(String[] args) {
        for (String s : TEST_CASES) {
            System.out.println(maskCreditCard(s));
        }
    }
}