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}