/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.commons.validator.routines.checkdigit;

/**
 * Modulus 11 <strong>ISBN-10</strong> Check Digit calculation/validation.
 * <p>
 * ISBN-10 Numbers are a numeric code except for the last (check) digit which can have a value of "X".
 * </p>
 * <p>
 * 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
 * weighted 1, the second 2 and so on. If the check digit is calculated as "10" it is converted to "X".
 * </p>
 * <p>
 * <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
 * the EAN-13 / UPC (see {@link EAN13CheckDigit}) standard.
 * </p>
 * <p>
 * For further information see:
 * </p>
 * <ul>
 * <li><a href="https://en.wikipedia.org/wiki/ISBN">Wikipedia - International Standard Book Number (ISBN)</a>.</li>
 * <li><a href="https://www.isbn.org/standards/home/isbn/transition.asp">ISBN-13 Transition details</a>.</li>
 * </ul>
 *
 * @since 1.4
 */
public final class ISBN10CheckDigit extends ModulusCheckDigit {

    private static final long serialVersionUID = 8000855044504864964L;

    /**
     * Singleton ISBN-10 Check Digit instance.
     */
    public static final CheckDigit ISBN10_CHECK_DIGIT = new ISBN10CheckDigit();

    /** An ISBN-10 is exactly ten characters, the last being the check digit. */
    private static final int ISBN10_LEN = 10;

    /**
     * Constructs a modulus 11 Check Digit routine for ISBN-10.
     */
    public ISBN10CheckDigit() {
        super(MODULUS_11);
    }

    /**
     * {@inheritDoc}
     *
     * <p>
     * The weight is {@code rightPos}, which does not change when a character is prepended, and modulus 11 makes the
     * leading position weight a multiple of the modulus, so {@code ModulusCheckDigit} would accept an over-length code
     * with any prepended digit (for example {@code 51930110995}). The ten-character length is checked here before the
     * check digit test.
     * </p>
     */
    @Override
    public boolean isValid(final String code) {
        return isLength(code, ISBN10_LEN) && super.isValid(code);
    }

    /**
     * Convert an integer value to a character at a specified position.
     * <p>
     * Value '10' for position 1 (check digit) converted to 'X'.
     * </p>
     *
     * @param charValue The integer value of the character.
     * @return The converted character.
     * @throws CheckDigitException if an error occurs.
     */
    @Override
    protected String toCheckDigit(final int charValue) throws CheckDigitException {
        if (charValue == 10) { // CHECKSTYLE IGNORE MagicNumber
            return "X";
        }
        return super.toCheckDigit(charValue);
    }

    /**
     * Convert a character at a specified position to an integer value.
     * <p>
     * Character 'X' check digit converted to 10.
     * </p>
     *
     * @param character The character to convert.
     * @param leftPos   The position of the character in the code, counting from left to right.
     * @param rightPos  The position of the character in the code, counting from right to left.
     * @return The integer value of the character.
     * @throws CheckDigitException if an error occurs.
     */
    @Override
    protected int toInt(final char character, final int leftPos, final int rightPos) throws CheckDigitException {
        if (rightPos == 1 && character == 'X') {
            return 10; // CHECKSTYLE IGNORE MagicNumber
        }
        return super.toInt(character, leftPos, rightPos);
    }

    /**
     * Calculates the <em>weighted</em> value of a character in the code at a specified position.
     *
     * <p>
     * For ISBN-10 (from right to left) digits are weighted by their position.
     * </p>
     *
     * @param charValue The numeric value of the character.
     * @param leftPos   The position of the character in the code, counting from left to right.
     * @param rightPos  The position of the character in the code, counting from right to left.
     * @return The weighted value of the character.
     */
    @Override
    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
        return charValue * rightPos;
    }
}
