/*
 * (c) Copyright 2008-2009 by Volker Bergmann. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, is permitted under the terms of the
 * GNU General Public License.
 *
 * For redistributing this software or a derivative work under a license other
 * than the GPL-compatible Free Software License as defined by the Free
 * Software Foundation or approved by OSI, you must first obtain a commercial
 * license to this software product from Volker Bergmann.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * WITHOUT A WARRANTY OF ANY KIND. ALL EXPRESS OR IMPLIED CONDITIONS,
 * REPRESENTATIONS AND WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE
 * HEREBY EXCLUDED. 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 org.databene.domain.person;

import javax.validation.ConstraintValidatorContext;

import org.databene.commons.validator.bean.AbstractConstraintValidator;

/**
 * Validates European Tax Identification Numbers.<br/>
 * <br/>
 * Created at 27.08.2008 00:06:33
 * @since 0.5.5
 * @author Volker Bergmann
 */
public class TINValidator extends AbstractConstraintValidator<TIN, String> {

    public boolean isValid(String number, ConstraintValidatorContext context) {
	    if (number == null || number.length() != 11)
			return false;
		boolean[] digitUsed = new boolean[10];
		// assure that at most one digit is used twice
		int doubleCount = 0;
		for (int i = 0; i < 10; i++) {
			int digit = number.charAt(i) - '0';
			boolean used = digitUsed[digit];
			if (!used)
				digitUsed[digit] = true;
			else {
				doubleCount++;
				if (doubleCount == 2)
					return false;
			}
		}
		// assure that there is exactly one digit used twice
		if (doubleCount == 0)
			return false;
		int checksum = calculateChecksum(number);
		return (number.charAt(10) == checksum + '0');
    }

	public static int calculateChecksum(String number) {
		int product = 0;
		for (int i = 0; i < 10; i++) {
			int sum = (number.charAt(i) - '0' + product) % 10;
			if (sum == 0) 
			    sum = 10;
			product = (sum * 2) % 11;
		}
		int checksum = 11 - product;
		if (checksum == 10)
			checksum = 0;
		return checksum;
	}

}