Credit Card Validation in C#

Credit Card Validation in C#

using System;

public enum CardType
{
MasterCard, BankCard, Visa, AmericanExpress, Discover, DinersClub, JCB
};

public sealed class CardValidator
{
private CardValidator() {} // static only

public static bool Validate(CardType cardType, string cardNumber)
{
byte[] number = new byte[16]; // number to validate

// Remove non-digits
int len = 0;
for(int i = 0; i < cardNumber.Length; i++)
{
if(char.IsDigit(cardNumber, i))
{
if(len == 16) return false; // number has too many digits
number[len++] = byte.Parse(cardNumber[i]);
}
}

// Validate based on card type, first if tests length, second tests prefix
switch(cardType)
{
case CardType.MasterCard:
if(len != 16)
return false;
if(number[0] != 5 || number[1] == 0 || number[1] > 5)
return false;
break;

case CardType.BankCard:
if(len != 16)
return false;
if(number[0] != 5 || number[1] != 6 || number[2] > 1)
return false;
break;

case CardType.Visa:
if(len != 16 && len != 13)
return false;
if(number[0] != 4)
return false;
break;

case CardType.AmericanExpress:
if(len != 15)
return false;
if(number[0] != 3 || (number[1] != 4 && number[1] != 7))
return false;
break;

case CardType.Discover:
if(len != 16)
return false;
if(number[0] != 6 || number[1] != 0 || number[2] != 1 || number[3] != 1)
return false;
break;

case CardType.DinersClub:
if(len != 14)
return false;
if(number[0] != 3 || (number[1] != 0 && number[1] != 6 && number[1] != 8)
|| number[1] == 0 && number[2] > 5)
return false;
break;

case CardType.JCB:
if(len != 16 && len != 15)
return false;
if(number[0] != 3 || number[1] != 5)
return false;
break;
}

// Use Luhn Algorithm to validate
int sum = 0;
for(int i = len - 1; i >= 0; i--)
{
if(i % 2 == len % 2)
{
int n = number[i] * 2;
sum += (n / 10) + (n % 10);
}
else
sum += number[i];
}
return (sum % 10 == 0);
}
}