using System;  

using System.Collections.Generic;  

using System.Linq;  

using System.Text;  

using System.Text.RegularExpressions; 

​

public class Program

{

    static int ii;

    public static void Main()

    {

        ii = 0;

        string pattern = @"^(?:[4,5,3,9][0-9]{3}(?:.{0,1})[0-9]{4}(?:.{0,1})[0-9]{4}(?:.{0,1})[0-9]{4})";

        //case test

        string[] creditabc = {"4221-0930-8100-1828","4221093081001828","4221 0930 8100 1828","4221|0930|8100|1828","4221_0930_8100_1828","4221.0930.8100.1828","4221gh0930dfgsd8100dfl1828"};

        Regex r = new Regex(pattern);

        foreach(string s in creditabc)

        {

            if (r.IsMatch(s))

            {

                Console.WriteLine("Final:" + Mod10Check(s));

                Console.WriteLine("CreditCard: {0} a valid ", s);

            }

            else

            {

                Console.WriteLine("CreditCard: {0} a not valid ", s);

            }

        }

    }

​

    public static bool Luhn(string digits)

    {

        Console.WriteLine("[");

        ii++;

        Console.WriteLine("STT: " + ii.ToString());

        Console.WriteLine("Befor: " + digits);

        var abc = digits.Reverse();

        Console.Write("After 1: ");

        foreach (var number in abc)

        {

           Console.Write(number.ToString() + "");

        }

        var abc1 = digits.Reverse().Select(c => c - 48);

        Console.Write("\n");

        Console.Write("After 2: ");

        foreach (var number in abc1)

        {

           Console.Write(number.ToString() + "");

        }

        Console.Write("\n");

        Console.WriteLine("]");

        return digits.All(char.IsDigit) && digits.Reverse().Where((e) => e >= '0' && e <= '9')

                    .Reverse()

                    .Select((e, i) => ((int)e - 48) * (i % 2 == 0 ? 1 : 2))

                    .Sum((e) => e / 10 + e % 10) % 10 == 0;

    }

    public static bool Mod10Check(string creditCardNumber)

    {

        //// check whether input string is null or empty

        Console.WriteLine("[DEBUG] Befor: " + creditCardNumber);

        if (string.IsNullOrEmpty(creditCardNumber))

        {

            return false;

        }

​

        //// 1. Starting with the check digit double the value of every other digit 

        //// 2. If doubling of a number results in a two digits number, add up

        ///   the digits to get a single digit number. This will results in eight single digit numbers                    

        //// 3. Get the sum of the digits

        //bool sumOfDigits = creditCardNumber.All(char.IsDigit) &&

        //              creditCardNumber.Reverse()

        //              .Select((e, i) => ((int)e - 48) * (i % 2 == 0 ? 1 : 2))

        //              .Sum((e) => e / 10 + e % 10) % 10 == 0;

        //378282246310005

        var sumOfDigits = creditCardNumber.Select((e, i) => ((int)e-48));

        Console.Write("[DEBUG] After 1 (input): ");

        foreach (var number in sumOfDigits)

        {

           Console.Write(number.ToString() + "");

        }

        var sumOfDigits4 = creditCardNumber.Reverse().Select((e, i) => ((int)e - 48) * (i % 2 == 0 ? 1 : 2));

        Console.Write("\n");

        Console.Write("[DEBUG] After 2 (To hop): ");

        foreach (var number in sumOfDigits4)

        {

           Console.Write(number.ToString() + "|");

        }

        Console.Write("\n");

        Console.Write("[DEBUG] After 3 (khong Reverse): ");

        var sumOfDigits5 = creditCardNumber.Select((e, i) => ((int)e - 48) * (i % 2 == 0 ? 1 : 2)).Sum((e) => e / 10 + e % 10);

        Console.Write(sumOfDigits5);

        var sumOfDigits2 = creditCardNumber.Reverse().Select((e, i) => ((int)e - 48) * (i % 2 == 0 ? 1 : 2)).Sum((e) => e / 10 + e % 10);

        Console.Write("\n");

        //Console.Write(sumOfDigits);

        //// If the final sum is divisible by 10, then the credit card number

        //   is valid. If it is not divisible by 10, the number is invalid.            

        int sumOfDigits1 = creditCardNumber.Where((e) => e >= '0' && e <= '9')

                        .Reverse()

                        .Select((e, i) => ((int)e - 48) * (i % 2 == 0 ? 1 : 2))

                        //.Sum((e) => e > 0 ? e / 10 + e % 10 : 0);

                        .Sum((e) => e / 10 + e % 10);

        Console.Write("[DEBUG]" + sumOfDigits1 + "|" + sumOfDigits2);

        Console.Write("\n");

        return sumOfDigits1 % 10 == 0;            

    }

}