/* Copyright (C) 2003-2007  The Chemistry Development Kit (CDK) project
 *
 * Contact: cdk-devel@lists.sourceforge.net
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1
 * of the License, or (at your option) any later version.
 * All we ask is that proper credit is given for our work, which includes
 * - but is not limited to - adding the above copyright notice to the beginning
 * of your source code files, and to any copyright notice that you may distribute
 * with programs based on this work.
 *
 * 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 */

package org.openscience.cdk.index;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Tools to work with CAS registry numbers.
 *
 * <br>
 * <b>References:</b>
 * <ul>
 * 	<li><a href="http://www.cas.org/EO/regsys.html">A CAS Registry Number</a></li>
 * 	<li><a href="http://www.cas.org/EO/checkdig.html">Check Digit Verification of CAS Registry Numbers</a></li>
 * </ul>
 *
 * @author Egon Willighagen &lt;egonw@sci.kun.nl&gt;
 * @cdk.githash
 * @author Nathana&euml;l "M.Le_maudit" Mazuir
 *
 * @see <a href="http://www.cas.org">CAS website</a>
 *
 * @cdk.created 2003-06-30
 * @cdk.keyword CAS number
 * @cdk.require java1.4+
 */
public class CASNumber {

    /**
     * Checks whether the registry number is valid.
     *
     * @param casNumber  the CAS number to validate
     * @cdk.keyword CAS number
     * @cdk.keyword validation
     * @return true if a valid CAS number, false otherwise
     */
    public static boolean isValid(String casNumber) {
        boolean overall = true;
        /*
         * check format
         */
        String format = "^(\\d+)-(\\d\\d)-(\\d)$";
        Pattern pattern = Pattern.compile(format);
        Matcher matcher = pattern.matcher(casNumber);
        overall = overall && matcher.matches();

        if (matcher.matches()) {
            /*
             * check number
             */
            String part1 = matcher.group(1);
            String part2 = matcher.group(2);
            String part3 = matcher.group(3);
            int part1value = Integer.parseInt(part1);
            if (part1value < 50) {
                overall = false;
                // CAS numbers start at 50-00-0
            } else {
                int digit = CASNumber.calculateCheckDigit(part1, part2);
                overall = overall && (digit == Integer.parseInt(part3));
            }
        }

        return overall;
    }

    private static int calculateCheckDigit(String part1, String part2) {
        int total = 0;
        total = total + 1 * Integer.parseInt(part2.substring(1, 2));
        total = total + 2 * Integer.parseInt(part2.substring(0, 1));
        int length = part1.length();
        for (int i = 0; i < length; i++) {
            total = total + (3 + i) * Integer.parseInt(part1.substring(length - 1 - i, length - i));
        }
        return total % 10;
    }
}
