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
019import java.io.Serializable;
020
021import org.apache.commons.validator.GenericValidator;
022
023/**
024 * <strong>Verhoeff</strong> (Dihedral) Check Digit calculation/validation.
025 * <p>
026 * Check digit calculation for numeric codes using a <a href="https://en.wikipedia.org/wiki/Dihedral_group">Dihedral Group</a> of order 10.
027 * </p>
028 * <p>
029 * See <a href="https://en.wikipedia.org/wiki/Verhoeff_algorithm">Wikipedia - Verhoeff algorithm</a> for more details.
030 * </p>
031 *
032 * @since 1.4
033 */
034public final class VerhoeffCheckDigit extends AbstractCheckDigit implements Serializable {
035
036    private static final long serialVersionUID = 4138993995483695178L;
037
038    /**
039     * Singleton Verhoeff Check Digit instance.
040     */
041    public static final CheckDigit VERHOEFF_CHECK_DIGIT = new VerhoeffCheckDigit();
042
043    /** D - multiplication table */
044    private static final int[][] D_TABLE = {
045        {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
046        {1, 2, 3, 4, 0, 6, 7, 8, 9, 5},
047        {2, 3, 4, 0, 1, 7, 8, 9, 5, 6},
048        {3, 4, 0, 1, 2, 8, 9, 5, 6, 7},
049        {4, 0, 1, 2, 3, 9, 5, 6, 7, 8},
050        {5, 9, 8, 7, 6, 0, 4, 3, 2, 1},
051        {6, 5, 9, 8, 7, 1, 0, 4, 3, 2},
052        {7, 6, 5, 9, 8, 2, 1, 0, 4, 3},
053        {8, 7, 6, 5, 9, 3, 2, 1, 0, 4},
054        {9, 8, 7, 6, 5, 4, 3, 2, 1, 0}};
055
056    /** P - permutation table */
057    private static final int[][] P_TABLE = {
058        {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
059        {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
060        {5, 8, 0, 3, 7, 9, 6, 1, 4, 2},
061        {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
062        {9, 4, 5, 3, 1, 2, 6, 8, 7, 0},
063        {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
064        {2, 7, 9, 3, 8, 0, 6, 4, 1, 5},
065        {7, 0, 4, 6, 9, 1, 3, 2, 5, 8}};
066
067    /** Inverse table */
068    private static final int[] INV_TABLE = {0, 4, 3, 2, 1, 5, 6, 7, 8, 9};
069
070    /**
071     * Constructs a new instance.
072     */
073    public VerhoeffCheckDigit() {
074        // empty
075    }
076
077    /**
078     * Calculate a Verhoeff <em>Check Digit</em> for a code.
079     *
080     * @param code The code to calculate the Check Digit for.
081     * @return The calculated Check Digit.
082     * @throws CheckDigitException if an error occurs calculating the check digit for the specified code.
083     */
084    @Override
085    public String calculate(final String code) throws CheckDigitException {
086        if (GenericValidator.isBlankOrNull(code)) {
087            throw new CheckDigitException("Code is missing");
088        }
089        return Integer.toString(INV_TABLE[calculateChecksum(code, false)]);
090    }
091
092    /**
093     * Calculate the checksum.
094     *
095     * @param code               The code to calculate the checksum for.
096     * @param includesCheckDigit Whether the code includes the Check Digit or not.
097     * @return The checksum value.
098     * @throws CheckDigitException if the code contains an invalid character (that is, a non-numeric character).
099     */
100    private int calculateChecksum(final String code, final boolean includesCheckDigit) throws CheckDigitException {
101        int checksum = 0;
102        for (int i = 0; i < code.length(); i++) {
103            final int idx = code.length() - (i + 1);
104            final char ch = code.charAt(idx);
105            if (!isAsciiDigit(ch)) {
106                throw new CheckDigitException("Invalid Character[%d] = '%d'", i, (int) ch);
107            }
108            final int num = ch - '0';
109            final int pos = includesCheckDigit ? i : i + 1;
110            checksum = D_TABLE[checksum][P_TABLE[pos % 8][num]]; // CHECKSTYLE IGNORE MagicNumber
111        }
112        return checksum;
113    }
114
115    /**
116     * Validate the Verhoeff <em>Check Digit</em> for a code.
117     *
118     * @param code The code to validate.
119     * @return {@code true} if the check digit is valid, otherwise {@code false}.
120     */
121    @Override
122    public boolean isValid(final String code) {
123        if (GenericValidator.isBlankOrNull(code)) {
124            return false;
125        }
126        try {
127            return calculateChecksum(code, true) == 0;
128        } catch (final CheckDigitException e) {
129            return false;
130        }
131    }
132}