LuhnMOD10.java

/*
 * Copyright (C) 2014 Jörg Prante
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published
 * by the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program; if not, see http://www.gnu.org/licenses
 * or write to the Free Software Foundation, Inc., 51 Franklin Street,
 * Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * The interactive user interfaces in modified source and object code
 * versions of this program must display Appropriate Legal Notices,
 * as required under Section 5 of the GNU Affero General Public License.
 *
 */
package org.xbib.standardnumber.check;

public class LuhnMOD10 implements Digit {

    @Override
    public String encode(String digits) {
        return digits + compute(digits);
    }

    @Override
    public boolean verify(String digits) {
        return computeSum(digits) % 10 == 0;
    }

    @Override
    public int compute(String digits) {
        int val = computeSum(digits);
        return (val == 0) ? 0 : (10 - val);
    }

    @Override
    public int getDigit(String digits) {
        return digits.charAt(digits.length() - 1) - '0';
    }

    @Override
    public String getNumber(String digits) {
        return digits.substring(0, digits.length() - 1);
    }

    private int computeSum(String digits) {
        int val = 0;
        for (int i = 0; i < digits.length(); i += 2) {
            int c = digits.charAt(i) - '0';
            val += c;
        }
        for (int i = 1; i < digits.length(); i += 2) {
            int c = digits.charAt(i) - '0';
            val += (c >= 5) ? (2*c - 9) : (2*c);
        }
        return val % 10;
    }
}