/* This script and many more are available free online at
The JavaScript Source!! http://javascript.internet.com
Created by: David Leppek :: https://www.azcode.com/Mod10

Basically, the alorithum takes each digit, from right to left and muliplies each second
digit by two. If the multiple is two-digits long (i.e.: 6 * 2 = 12) the two digits of
the multiple are then added together for a new number (1 + 2 = 3). You then add up the 
string of numbers, both unaltered and new values and get a total sum. This sum is then
divided by 10 and the remainder should be zero if it is a valid credit card. Hense the
name Mod 10 or Modulus 10. */
function validCcard(ccNumbi)
{  // v2.0
	var valid = "0123456789"  // Valid digits in a credit card number
	var ccNumb = ccNumbi;
	ccNumb = ccNumbi.replace(/[- ]/gi,"");
	var len = ccNumb.length;  // The length of the submitted cc number
	var iCCN = parseInt(ccNumb);  // integer of ccNumb
	var sCCN = ccNumb.toString();  // string of ccNumb
	sCCN = sCCN.replace (/^\s+|\s+$/g,'');  // strip spaces
	var iTotal = 0;  // integer total set at zero
	var bNum = true;  // by default assume it is a number
	var bResult = false;  // by default assume it is NOT a valid cc
	var temp;  // temp variable for parsing string
	var calc;  // used for calculation of each digit

// Determine if the ccNumb is in fact all numbers
	for (var j=0; j<len; j++)
	{	temp = "" + sCCN.substring(j, j+1);
		if (valid.indexOf(temp) == "-1"){bNum = false;}
	}

// if it is NOT a number, you can either alert to the fact, or just pass a failure
	if(!bNum)
	{	/*alert("Not a Number");*/bResult = false;
	}

// Determine if it is the proper length 
	if((len == 0)&&(bResult))
	{	// nothing, field is blank AND passed above # check
		bResult = false;
	} else
	{  // ccNumb is a number and the proper length - let's see if it is a valid card number
		if(len >= 15)
		{	// 15 or 16 for Amex or V/MC
			for(var i=len;i>0;i--)
			{  // LOOP throught the digits of the card
				calc = parseInt(iCCN) % 10;  // right most digit
				calc = parseInt(calc);  // assure it is an integer
				iTotal += calc;  // running total of the card number as we loop - Do Nothing to first digit
				i--;  // decrement the count - move to the next digit in the card
				iCCN = iCCN / 10;                               // subtracts right most digit from ccNumb
				calc = parseInt(iCCN) % 10 ;    // NEXT right most digit
				calc = calc *2;                                 // multiply the digit by two
				// Instead of some screwy method of converting 16 to a string and then parsing 1 and 6 and then adding them to make 7,
				// I use a simple switch statement to change the value of calc2 to 7 if 16 is the multiple.
				switch(calc)
				{	case 10: calc = 1; break;       //5*2=10 & 1+0 = 1
					case 12: calc = 3; break;       //6*2=12 & 1+2 = 3
					case 14: calc = 5; break;       //7*2=14 & 1+4 = 5
					case 16: calc = 7; break;       //8*2=16 & 1+6 = 7
					case 18: calc = 9; break;       //9*2=18 & 1+8 = 9
					default: calc = calc;           //4*2= 8 &   8 = 8  -same for all lower numbers
				}                                               
				iCCN = iCCN / 10;  // subtracts right most digit from ccNum
				iTotal += calc;  // running total of the card number as we loop
			}  // END OF LOOP
			if ((iTotal%10)==0)
			{  // check to see if the sum Mod 10 is zero
				bResult = true;  // This IS (or could be) a valid credit card number.
			} else
			{	bResult = false;  // This could NOT be a valid credit card number
			}
		}
	}
	return bResult;
}