/*
 * Copyright (c) 2003-onwards Shaven Puppy Ltd
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 *
 * * Neither the name of 'Shaven Puppy' nor the names of its contributors
 *   may be used to endorse or promote products derived from this software
 *   without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package net.puppygames.gamecommerce.shared;

/**
 * The Luhn mod-10 credit card number checking algorithm
 * @author cas
 */
public final class Luhn {

	/**
	 * No constructor
	 */
	private Luhn() {
	}

	/**
	 * Validates a credit card number according to the Luhn formula given on
	 * <a href="http://www.beachnet.com/~hstiles/cardtype.html">this site</a>
	 * @param number The credit card number to check
	 * @return true if the number is valid
	 */
	public static boolean check(String number) {
		int n = number.length() - 1;
		int sum = 0;
		boolean mult = false;

		for (int i = n; i >= 0; i --) {
			int val = Integer.parseInt(number.substring(i, i + 1));
			if (mult) {
				val <<= 1;
			}
			if (val < 10) {
				sum += val;
			} else {
				sum += 1 + (val - 10);
			}
			mult = !mult;
		}

		return sum % 10 == 0;
	}
}