public class MaximaBarcodeCheckDigit extends ModulusCheckDigit {

    private static final int[] POSITION_WEIGHT = new int[] {3, 1};

    /** Singleton Luhn Check Digit instance */
    public static final CheckDigit MAXIMA_CHECK_DIGIT = new MaximaBarcodeCheckDigit();

    public MaximaBarcodeCheckDigit() {
        super(10);
    }

    @Override
    protected int weightedValue(int charValue, int leftPos, int rightPos) throws CheckDigitException {
        int weight = POSITION_WEIGHT[rightPos % 2];
        int weightedValue = (charValue * weight);
        if(weightedValue > 9){
            weightedValue = 1 + (weightedValue % 10);
        }
        return weightedValue;
    }

    @Override
    protected int toInt(char character, int leftPos, int rightPos) throws CheckDigitException {
        if (Character.isLetter(character)) {
            return (int) character;
        } else if(Character.isDigit(character)){
            return Character.getNumericValue(character);
        } else {
            throw new CheckDigitException("Invalid Character[" +
                    leftPos + "] = '" + character + "'");
        }
    }

    /**
     * Calculate the modulus for a code.
     *
     * @param code The code to calculate the modulus for.
     * @param includesCheckDigit Whether the code includes the Check Digit or not.
     * @return The modulus value
     * @throws CheckDigitException if an error occurs calculating the modulus
     * for the specified code
     */
    protected int calculateModulus(String code, boolean includesCheckDigit) throws CheckDigitException {
        int total = 0;
        for (int i = 0; i < code.length(); i++) {
            int lth = code.length() + (includesCheckDigit ? 0 : 1);
            int leftPos  = i + 1;
            int rightPos = lth - i;
            int charValue = toInt(code.charAt(i), leftPos, rightPos);
            total += weightedValue(charValue, leftPos, rightPos);
        }
        if (total == 0) {
            throw new CheckDigitException("Invalid code, sum is zero");
        }
        return (10 - (total % 10)) % 10;
    }

}