001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.validator.routines.checkdigit;
018
019/**
020 * Modulus 10 <strong>EAN-13</strong> / <strong>UPC</strong> / <strong>ISBN-13</strong> Check Digit
021 * calculation/validation.
022 * <p>
023 * Check digit calculation is based on <em>modulus 10</em> with digits in
024 * an <em>odd</em> position (from right to left) being weighted 1 and <em>even</em>
025 * position digits being weighted 3.
026 * </p>
027 * <p>
028 * For further information see:
029 * </p>
030 * <ul>
031 *   <li>EAN-13 - see
032 *       <a href="https://en.wikipedia.org/wiki/European_Article_Number">Wikipedia -
033 *       European Article Number</a>.</li>
034 *   <li>UPC - see
035 *       <a href="https://en.wikipedia.org/wiki/Universal_Product_Code">Wikipedia -
036 *       Universal Product Code</a>.</li>
037 *   <li>ISBN-13 - see
038 *       <a href="https://en.wikipedia.org/wiki/ISBN">Wikipedia - International
039 *       Standard Book Number (ISBN)</a>.</li>
040 * </ul>
041 *
042 * @since 1.4
043 */
044public final class EAN13CheckDigit extends ModulusCheckDigit {
045
046    private static final long serialVersionUID = 1726347093230424107L;
047
048    /**
049     * Singleton EAN-13 Check Digit instance.
050     */
051    public static final CheckDigit EAN13_CHECK_DIGIT = new EAN13CheckDigit();
052
053    /** Weighting given to digits depending on their right position */
054    private static final int[] POSITION_WEIGHT = {3, 1};
055
056    /** An EAN-13 (and ISBN-13) code is exactly thirteen digits, the last being the check digit. */
057    private static final int EAN13_LEN = 13;
058
059    /**
060     * Constructs a modulus 10 Check Digit routine for EAN/UPC.
061     */
062    public EAN13CheckDigit() {
063    }
064
065    /**
066     * {@inheritDoc}
067     *
068     * <p>
069     * The weight is taken from {@code rightPos}, which does not change when a character is prepended, so
070     * {@code ModulusCheckDigit} would accept an over-length code whose leading digit lands on a no-op weight (for
071     * example a valid code with a {@code 0} prepended). The thirteen-character length is checked here before the check
072     * digit test.
073     * </p>
074     */
075    @Override
076    public boolean isValid(final String code) {
077        return isLength(code, EAN13_LEN) && super.isValid(code);
078    }
079
080    /**
081     * Calculates the <em>weighted</em> value of a character in the code at a specified position.
082     * <p>
083     * For EAN-13 (from right to left) <strong>odd</strong> digits are weighted with a factor of <strong>one</strong> and <strong>even</strong> digits with a
084     * factor of <strong>three</strong>.
085     * </p>
086     *
087     * @param charValue The numeric value of the character.
088     * @param leftPos   The position of the character in the code, counting from left to right.
089     * @param rightPos  The position of the character in the code, counting from right to left.
090     * @return The weighted value of the character.
091     */
092    @Override
093    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
094        return charValue * POSITION_WEIGHT[rightPos % 2];
095    }
096}