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 */
017
018package org.apache.commons.validator.routines.checkdigit;
019
020/**
021 * Modulus 11 <strong>ISBN-10</strong> Check Digit calculation/validation.
022 * <p>
023 * ISBN-10 Numbers are a numeric code except for the last (check) digit which can have a value of "X".
024 * </p>
025 * <p>
026 * Check digit calculation is based on <em>modulus 11</em> with digits being weighted based by their position, from right to left with the first digit being
027 * weighted 1, the second 2 and so on. If the check digit is calculated as "10" it is converted to "X".
028 * </p>
029 * <p>
030 * <strong>N.B.</strong> From 1st January 2007 the book industry will start to use a new 13 digit ISBN number (rather than this 10 digit ISBN number) which uses
031 * the EAN-13 / UPC (see {@link EAN13CheckDigit}) standard.
032 * </p>
033 * <p>
034 * For further information see:
035 * </p>
036 * <ul>
037 * <li><a href="https://en.wikipedia.org/wiki/ISBN">Wikipedia - International Standard Book Number (ISBN)</a>.</li>
038 * <li><a href="https://www.isbn.org/standards/home/isbn/transition.asp">ISBN-13 Transition details</a>.</li>
039 * </ul>
040 *
041 * @since 1.4
042 */
043public final class ISBN10CheckDigit extends ModulusCheckDigit {
044
045    private static final long serialVersionUID = 8000855044504864964L;
046
047    /**
048     * Singleton ISBN-10 Check Digit instance.
049     */
050    public static final CheckDigit ISBN10_CHECK_DIGIT = new ISBN10CheckDigit();
051
052    /** An ISBN-10 is exactly ten characters, the last being the check digit. */
053    private static final int ISBN10_LEN = 10;
054
055    /**
056     * Constructs a modulus 11 Check Digit routine for ISBN-10.
057     */
058    public ISBN10CheckDigit() {
059        super(MODULUS_11);
060    }
061
062    /**
063     * {@inheritDoc}
064     *
065     * <p>
066     * The weight is {@code rightPos}, which does not change when a character is prepended, and modulus 11 makes the
067     * leading position weight a multiple of the modulus, so {@code ModulusCheckDigit} would accept an over-length code
068     * with any prepended digit (for example {@code 51930110995}). The ten-character length is checked here before the
069     * check digit test.
070     * </p>
071     */
072    @Override
073    public boolean isValid(final String code) {
074        return isLength(code, ISBN10_LEN) && super.isValid(code);
075    }
076
077    /**
078     * Convert an integer value to a character at a specified position.
079     * <p>
080     * Value '10' for position 1 (check digit) converted to 'X'.
081     * </p>
082     *
083     * @param charValue The integer value of the character.
084     * @return The converted character.
085     * @throws CheckDigitException if an error occurs.
086     */
087    @Override
088    protected String toCheckDigit(final int charValue) throws CheckDigitException {
089        if (charValue == 10) { // CHECKSTYLE IGNORE MagicNumber
090            return "X";
091        }
092        return super.toCheckDigit(charValue);
093    }
094
095    /**
096     * Convert a character at a specified position to an integer value.
097     * <p>
098     * Character 'X' check digit converted to 10.
099     * </p>
100     *
101     * @param character The character to convert.
102     * @param leftPos   The position of the character in the code, counting from left to right.
103     * @param rightPos  The position of the character in the code, counting from right to left.
104     * @return The integer value of the character.
105     * @throws CheckDigitException if an error occurs.
106     */
107    @Override
108    protected int toInt(final char character, final int leftPos, final int rightPos) throws CheckDigitException {
109        if (rightPos == 1 && character == 'X') {
110            return 10; // CHECKSTYLE IGNORE MagicNumber
111        }
112        return super.toInt(character, leftPos, rightPos);
113    }
114
115    /**
116     * Calculates the <em>weighted</em> value of a character in the code at a specified position.
117     *
118     * <p>
119     * For ISBN-10 (from right to left) digits are weighted by their position.
120     * </p>
121     *
122     * @param charValue The numeric value of the character.
123     * @param leftPos   The position of the character in the code, counting from left to right.
124     * @param rightPos  The position of the character in the code, counting from right to left.
125     * @return The weighted value of the character.
126     */
127    @Override
128    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
129        return charValue * rightPos;
130    }
131}