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 *      http://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 11 <b>ISBN-10</b> Check Digit calculation/validation.
021 * <p>
022 * ISBN-10 Numbers are a numeric code except for the last (check) digit
023 * which can have a value of "X".
024 * <p>
025 * Check digit calculation is based on <i>modulus 11</i> with digits being weighted
026 * based by their position, from right to left  with the first digit being weighted
027 * 1, the second 2 and so on. If the check digit is calculated as "10" it is converted
028 * to "X".
029 * <p>
030 * <b>N.B.</b> From 1st January 2007 the book industry will start to use a new 13 digit
031 * ISBN number (rather than this 10 digit ISBN number) which uses the EAN-13 / UPC
032 * (see {@link EAN13CheckDigit}) standard.
033 * <p>
034 * For further information see:
035 * <ul>
036 *   <li><a href="https://en.wikipedia.org/wiki/ISBN">Wikipedia - International
037 *       Standard Book Number (ISBN)</a>.</li>
038 *   <li><a href="http://www.isbn.org/standards/home/isbn/transition.asp">ISBN-13
039 *       Transition details</a>.</li>
040 * </ul>
041 *
042 * @since 1.4
043 */
044public final class ISBN10CheckDigit extends ModulusCheckDigit {
045
046    private static final long serialVersionUID = 8000855044504864964L;
047
048    /** Singleton ISBN-10 Check Digit instance */
049    public static final CheckDigit ISBN10_CHECK_DIGIT = new ISBN10CheckDigit();
050
051    /**
052     * Constructs a modulus 11 Check Digit routine for ISBN-10.
053     */
054    public ISBN10CheckDigit() {
055        super(MODULUS_11);
056    }
057
058    /**
059     * <p>Convert an integer value to a character at a specified position.</p>
060     *
061     * <p>Value '10' for position 1 (check digit) converted to 'X'.</p>
062     *
063     * @param charValue The integer value of the character.
064     * @return The converted character.
065     * @throws CheckDigitException if an error occurs.
066     */
067    @Override
068    protected String toCheckDigit(final int charValue)
069            throws CheckDigitException {
070        if (charValue == 10) {  // CHECKSTYLE IGNORE MagicNumber
071            return "X";
072        }
073        return super.toCheckDigit(charValue);
074    }
075
076    /**
077     * <p>Convert a character at a specified position to an
078     * integer value.</p>
079     *
080     * <p>Character 'X' check digit converted to 10.</p>
081     *
082     * @param character The character to convert.
083     * @param leftPos The position of the character in the code, counting from left to right
084     * @param rightPos The position of the character in the code, counting from right to left
085     * @return The integer value of the character.
086     * @throws CheckDigitException if an error occurs.
087     */
088    @Override
089    protected int toInt(final char character, final int leftPos, final int rightPos)
090            throws CheckDigitException {
091        if (rightPos == 1 && character == 'X') {
092            return 10;  // CHECKSTYLE IGNORE MagicNumber
093        }
094        return super.toInt(character, leftPos, rightPos);
095    }
096
097    /**
098     * Calculates the <i>weighted</i> value of a character in the
099     * code at a specified position.
100     *
101     * <p>For ISBN-10 (from right to left) digits are weighted
102     * by their position.</p>
103     *
104     * @param charValue The numeric value of the character.
105     * @param leftPos The position of the character in the code, counting from left to right
106     * @param rightPos The positionof the character in the code, counting from right to left
107     * @return The weighted value of the character.
108     */
109    @Override
110    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
111        return charValue * rightPos;
112    }
113
114}