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