    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 org.apache.commons.validator.GenericValidator;
    020import org.apache.commons.validator.routines.CodeValidator;
    021
    022/**
    023 * Modulus 10 <strong>CAS Registry Number</strong> (or <strong>Chemical Abstracts Service</strong> (CAS RN)) Check Digit
    024 * calculation/validation.
    025 *
    026 * <p>
    027 * CAS Numbers are unique identification numbers used
    028 * to identify chemical substance described in the open scientific literature.
    029 * </p>
    030 *
    031 * <p>
    032 * Check digit calculation is based on <em>modulus 10</em> with digits being weighted
    033 * based on their position (from right to left).
    034 * </p>
    035 *
    036 * <p>
    037 * The check digit is found by taking the last digit times 1, the preceding digit times 2,
    038 * the preceding digit times 3 etc., adding all these up and computing the sum modulo 10.
    039 * For example, the CAS number of water is {@code 7732-18-5}:
    040 * the checksum 5 is calculated as (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5.
    041 * </p>
    042 *
    043 * <p>
    044 * For further information see
    045 *  <a href="https://en.wikipedia.org/wiki/CAS_Registry_Number">Wikipedia - CAS Registry Number</a>.
    046 * </p>
    047 *
    048 * @since 1.9.0
    049 */
    050public final class CASNumberCheckDigit extends ModulusCheckDigit {
    051
    052    private static final long serialVersionUID = -5387334603220786657L;
    053
    054    /** Singleton Check Digit instance. */
    055    private static final CASNumberCheckDigit INSTANCE = new CASNumberCheckDigit();
    056
    057    /**
    058     * CAS number consists of 3 groups of numbers separated dashes (-).
    059     * First group has 2 to 7 digits.
    060     * Example: water is 7732-18-5
    061     */
    062    private static final String GROUP1 = "(\\d{2,7})";
    063
    064    private static final String DASH = "(?:\\-)";
    065    static final String CAS_REGEX = "^(?:" + GROUP1 + DASH + "(\\d{2})" + DASH + "(\\d))$";
    066    private static final int CAS_MIN_LEN = 4; // 9-99-9 LEN without SEP
    067
    068    /** Maximum capacity of 1,000,000,000 == 9999999-99-9*/
    069    private static final int CAS_MAX_LEN = 10;
    070    static final CodeValidator REGEX_VALIDATOR = new CodeValidator(CAS_REGEX, CAS_MIN_LEN, CAS_MAX_LEN, null);
    071
    072    /** Weighting given to digits depending on their right position */
    073    private static final int[] POSITION_WEIGHT = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    074
    075    /**
    076     * Gets the singleton instance of this validator.
    077     *
    078     * @return A singleton instance of the CAS Number validator.
    079     */
    080    public static CheckDigit getInstance() {
    081        return INSTANCE;
    082    }
    083
    084    /**
    085     * Constructs a modulus 10 Check Digit routine for CAS Numbers.
    086     */
    087    private CASNumberCheckDigit() {
    088    }
    089
    090    /**
    091     * {@inheritDoc}
    092     */
    093    @Override
    094    public String calculate(final String code) throws CheckDigitException {
    095        if (GenericValidator.isBlankOrNull(code)) {
    096            throw new CheckDigitException("Code is missing");
    097        }
    098        return toCheckDigit(INSTANCE.calculateModulus(code, false));
    099    }
    100
    101    /**
    102     * {@inheritDoc}
    103     */
    104    @Override
    105    public boolean isValid(final String code) {
    106        if (GenericValidator.isBlankOrNull(code)) {
    107            return false;
    108        }
    109        final Object cde = REGEX_VALIDATOR.validate(code);
    110        if (!(cde instanceof String)) {
    111            return false;
    112        }
    113        final String validated = (String) cde;
    114        try {
    115            return INSTANCE.calculateModulus(validated, true) == Character.getNumericValue(validated.charAt(validated.length() - 1));
    116        } catch (final CheckDigitException e) {
    117            return false;
    118        }
    119    }
    120
    121    /**
    122     * Calculates the <em>weighted</em> value of a character in the code at a specified position.
    123     * <p>
    124     * CAS numbers are weighted in the following manner:
    125     * </p>
    126     * <pre>{@code
    127     *    right position: 1  2  3  4  5  6  7  8  9 10
    128     *            weight: 1  2  3  4  5  6  7  8  9  0
    129     * }</pre>
    130     *
    131     * @param charValue The numeric value of the character.
    132     * @param leftPos The position of the character in the code, counting from left to right.
    133     * @param rightPos The position of the character in the code, counting from right to left.
    134     * @return The weighted value of the character.
    135     */
    136    @Override
    137    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
    138        final int weight = POSITION_WEIGHT[(rightPos - 1) % MODULUS_10];
    139        return charValue * weight;
    140    }
    141
    142}