Luhn Algorithm: How to get check digit of MOD 10v1 in Batch Apex Class?

Question

I would like to ask some help on how I can get the Mod 10 check digit of Contact.DonorID. the result should be

Contact.CRN__c = Contact.DonorID + CheckDigit

Just like this:

Check Digit is 2

CRN: 00184572

It is my first time to do it and I don't have any idea, I've been struggling for 3 days searching about it. I found this link -- Luhn algorithm check digit in formula field but it is using formula field, so, it can't help me.

Thank you in advance!

Answer 1

This is pretty simple, you just need to implement the algorithm.

static Integer accumulate(String[] digits, Boolean validate) {
    // This algorithm goes from the *left*, so we need to know which to double
    Integer checkSize = validate? 1: 0;
    Integer accumulator = 0;
    while(!digits.isEmpty()) {
        Integer nextDigit = Integer.valueOf(digits.remove(0));
        // We should double the value when true
        if((digits.size()&1) == checkSize) {
            nextDigit <<= 1;
            // And "add together" the individual digits when 10+
            if(nextDigit > 9) {
                nextDigit -= 9;
            }
        }
        accumulator += nextDigit;
    }
    return accumulator;
}
// Returns true if the valid Luhn check digit present
public static Boolean validateLuhnCheckDigit(String source) {
    return 0 == Math.mod(accumulate(source.split(''), true), 10);
}
// Returns the check digit for a given string
public static String calculateLuhnCheckDigit(String source) {
    return ''+Math.mod(accumulate(source.split(''), false) * 9, 10);
}

No error checking is provided, and is left as an exercise to the reader.

Answer 2

I got it and it's working! I'll share my apex code. You can test it on Anonymous Window.

                String donorId = Contact.DonorID__c;
                Integer sum = 0;
                String resultCRN;
                Integer l = donorId.length();
                
                for(Integer i=l-1;i>=0;i--){
                    Integer num = Integer.ValueOf(donorId.substring(i,i+1));
                    if (math.mod(i, 2) == math.mod(l, 2))
                    {
                        Integer n = num * 2;
                        sum += (n / 10) + (math.mod(n, 10));
                    }
                    else{
                        sum += num;
                    }
                }
                resultCRN= donorId + sum;
                Contact.CRN__c = resultCRN;
                System.debug('Donor ID is: ' + donorId );
                System.debug('Check digit result is: ' + sum);
                System.debug('CRN is: ' + resultCRN);