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
027 * <a href="https://en.wikipedia.org/wiki/Dihedral_group">Dihedral Group</a>
028 * of order 10.
029 * <p>
030 * See <a href="https://en.wikipedia.org/wiki/Verhoeff_algorithm">Wikipedia
031 *  - Verhoeff algorithm</a> for more details.
032 *
033 * @since 1.4
034 */
035public final class VerhoeffCheckDigit extends AbstractCheckDigit implements Serializable {
036
037    private static final long serialVersionUID = 4138993995483695178L;
038
039    /** Singleton Verhoeff Check Digit instance */
040    public static final CheckDigit VERHOEFF_CHECK_DIGIT = new VerhoeffCheckDigit();
041
042    /** D - multiplication table */
043    private static final int[][] D_TABLE = {
044        {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
045        {1, 2, 3, 4, 0, 6, 7, 8, 9, 5},
046        {2, 3, 4, 0, 1, 7, 8, 9, 5, 6},
047        {3, 4, 0, 1, 2, 8, 9, 5, 6, 7},
048        {4, 0, 1, 2, 3, 9, 5, 6, 7, 8},
049        {5, 9, 8, 7, 6, 0, 4, 3, 2, 1},
050        {6, 5, 9, 8, 7, 1, 0, 4, 3, 2},
051        {7, 6, 5, 9, 8, 2, 1, 0, 4, 3},
052        {8, 7, 6, 5, 9, 3, 2, 1, 0, 4},
053        {9, 8, 7, 6, 5, 4, 3, 2, 1, 0}};
054
055    /** P - permutation table */
056    private static final int[][] P_TABLE = {
057        {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
058        {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
059        {5, 8, 0, 3, 7, 9, 6, 1, 4, 2},
060        {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
061        {9, 4, 5, 3, 1, 2, 6, 8, 7, 0},
062        {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
063        {2, 7, 9, 3, 8, 0, 6, 4, 1, 5},
064        {7, 0, 4, 6, 9, 1, 3, 2, 5, 8}};
065
066    /** Inverse table */
067    private static final int[] INV_TABLE = {0, 4, 3, 2, 1, 5, 6, 7, 8, 9};
068
069    /**
070     * Constructs a new instance.
071     */
072    public VerhoeffCheckDigit() {
073        // empty
074    }
075
076    /**
077     * Calculate a Verhoeff <em>Check Digit</em> for a code.
078     *
079     * @param code The code to calculate the Check Digit for
080     * @return The calculated Check Digit
081     * @throws CheckDigitException if an error occurs calculating
082     * 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        final int checksum = calculateChecksum(code, false);
090        return Integer.toString(INV_TABLE[checksum]);
091    }
092
093    /**
094     * Calculate the checksum.
095     *
096     * @param code The code to calculate the checksum for.
097     * @param includesCheckDigit Whether the code includes the Check Digit or not.
098     * @return The checksum value
099     * @throws CheckDigitException if the code contains an invalid character (that is, a non-numeric character)
100     */
101    private int calculateChecksum(final String code, final boolean includesCheckDigit) throws CheckDigitException {
102        int checksum = 0;
103        for (int i = 0; i < code.length(); i++) {
104            final int idx = code.length() - (i + 1);
105            final int num = Character.getNumericValue(code.charAt(idx));
106            if (num < 0 || num > 9) { // CHECKSTYLE IGNORE MagicNumber
107                throw new CheckDigitException("Invalid Character[" +
108                        i + "] = '" + (int) code.charAt(idx) + "'");
109            }
110            final int pos = includesCheckDigit ? i : i + 1;
111            checksum = D_TABLE[checksum][P_TABLE[pos % 8][num]]; // CHECKSTYLE IGNORE MagicNumber
112        }
113        return checksum;
114    }
115
116    /**
117     * Validate the Verhoeff <em>Check Digit</em> for a code.
118     *
119     * @param code The code to validate
120     * @return {@code true} if the check digit is valid,
121     * otherwise {@code false}
122     */
123    @Override
124    public boolean isValid(final String code) {
125        if (GenericValidator.isBlankOrNull(code)) {
126            return false;
127        }
128        try {
129            return calculateChecksum(code, true) == 0;
130        } catch (final CheckDigitException e) {
131            return false;
132        }
133    }
134
135}