    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 * @version $Revision$
    032 * @since Validator 1.4
    033 */
    034public final class VerhoeffCheckDigit implements CheckDigit, Serializable {
    035
    036    private static final long serialVersionUID = 4138993995483695178L;
    037
    038    /** Singleton Verhoeff Check Digit instance */
    039    public static final CheckDigit VERHOEFF_CHECK_DIGIT = new VerhoeffCheckDigit();
    040
    041    /** D - multiplication table */
    042    private static final int[][] D_TABLE = new int[][] {
    043        {0,  1,  2,  3,  4,  5,  6,  7,  8,  9},
    044        {1,  2,  3,  4,  0,  6,  7,  8,  9,  5},
    045        {2,  3,  4,  0,  1,  7,  8,  9,  5,  6},
    046        {3,  4,  0,  1,  2,  8,  9,  5,  6,  7},
    047        {4,  0,  1,  2,  3,  9,  5,  6,  7,  8},
    048        {5,  9,  8,  7,  6,  0,  4,  3,  2,  1},
    049        {6,  5,  9,  8,  7,  1,  0,  4,  3,  2},
    050        {7,  6,  5,  9,  8,  2,  1,  0,  4,  3},
    051        {8,  7,  6,  5,  9,  3,  2,  1,  0,  4},
    052        {9,  8,  7,  6,  5,  4,  3,  2,  1,  0}};
    053
    054    /** P - permutation table */
    055    private static final int[][] P_TABLE = new int[][] {
    056        {0,  1,  2,  3,  4,  5,  6,  7,  8,  9},
    057        {1,  5,  7,  6,  2,  8,  3,  0,  9,  4},
    058        {5,  8,  0,  3,  7,  9,  6,  1,  4,  2},
    059        {8,  9,  1,  6,  0,  4,  3,  5,  2,  7},
    060        {9,  4,  5,  3,  1,  2,  6,  8,  7,  0},
    061        {4,  2,  8,  6,  5,  7,  3,  9,  0,  1},
    062        {2,  7,  9,  3,  8,  0,  6,  4,  1,  5},
    063        {7,  0,  4,  6,  9,  1,  3,  2,  5,  8}};
    064
    065    /** inv: inverse table */
    066    private static final int[] INV_TABLE = new int[]
    067        {0,  4,  3,  2,  1,  5,  6,  7,  8,  9};
    068
    069
    070    /**
    071     * Validate the Verhoeff <i>Check Digit</i> for a code.
    072     *
    073     * @param code The code to validate
    074     * @return <code>true</code> if the check digit is valid,
    075     * otherwise <code>false</code>
    076     */
    077    @Override
    078    public boolean isValid(String code) {
    079        if (code == null || code.length() == 0) {
    080            return false;
    081        }
    082        try {
    083            return (calculateChecksum(code, true) == 0);
    084        } catch (CheckDigitException e) {
    085            return false;
    086        }
    087    }
    088
    089    /**
    090     * Calculate a Verhoeff <i>Check Digit</i> for a code.
    091     *
    092     * @param code The code to calculate the Check Digit for
    093     * @return The calculated Check Digit
    094     * @throws CheckDigitException if an error occurs calculating
    095     * the check digit for the specified code
    096     */
    097    @Override
    098    public String calculate(String code) throws CheckDigitException {
    099        if (code == null || code.length() == 0) {
    100            throw new CheckDigitException("Code is missing");
    101        }
    102        int checksum = calculateChecksum(code, false);
    103        return Integer.toString(INV_TABLE[checksum]);
    104    }
    105
    106    /**
    107     * Calculate the checksum.
    108     *
    109     * @param code The code to calculate the checksum for.
    110     * @param includesCheckDigit Whether the code includes the Check Digit or not.
    111     * @return The checksum value
    112     * @throws CheckDigitException if the code contains an invalid character (i.e. not numeric)
    113     */
    114    private int calculateChecksum(String code, boolean includesCheckDigit) throws CheckDigitException {
    115        int checksum = 0;
    116        for (int i = 0; i < code.length(); i++) {
    117            int idx = code.length() - (i + 1);
    118            int num = Character.getNumericValue(code.charAt(idx));
    119            if (num < 0 || num > 9) { // CHECKSTYLE IGNORE MagicNumber
    120                throw new CheckDigitException("Invalid Character[" +
    121                        i + "] = '" + ((int)code.charAt(idx)) + "'");
    122            }
    123            int pos = includesCheckDigit ? i : i + 1;
    124            checksum = D_TABLE[checksum][P_TABLE[pos % 8][num]]; // CHECKSTYLE IGNORE MagicNumber
    125        }
    126        return checksum;
    127    }
    128
    129}