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
019/**
020 * Modulus 10 <b>ISIN</b> (International Securities Identifying Number) Check Digit calculation/validation.
021 *
022 * <p>
023 * ISIN Numbers are 12 character alphanumeric codes used
024 * to identify Securities.
025 * </p>
026 *
027 * <p>
028 * Check digit calculation uses the <i>Modulus 10 Double Add Double</i> technique
029 * with every second digit being weighted by 2. Alphabetic characters are
030 * converted to numbers by their position in the alphabet starting with A being 10.
031 * Weighted numbers greater than ten are treated as two separate numbers.
032 * </p>
033 *
034 * <p>
035 * See <a href="http://en.wikipedia.org/wiki/ISIN">Wikipedia - ISIN</a>
036 * for more details.
037 * </p>
038 *
039 * @version $Revision: 1739356 $
040 * @since Validator 1.4
041 */
042public final class ISINCheckDigit extends ModulusCheckDigit {
043
044    private static final long serialVersionUID = -1239211208101323599L;
045
046    private static final int MAX_ALPHANUMERIC_VALUE = 35; // Character.getNumericValue('Z')
047
048    /** Singleton ISIN Check Digit instance */
049    public static final CheckDigit ISIN_CHECK_DIGIT = new ISINCheckDigit();
050
051    /** weighting given to digits depending on their right position */
052    private static final int[] POSITION_WEIGHT = new int[] {2, 1};
053
054    /**
055     * Construct an ISIN Indetifier Check Digit routine.
056     */
057    public ISINCheckDigit() {
058        super(10); // CHECKSTYLE IGNORE MagicNumber
059    }
060
061    /**
062     * Calculate the modulus for an ISIN code.
063     *
064     * @param code The code to calculate the modulus for.
065     * @param includesCheckDigit Whether the code includes the Check Digit or not.
066     * @return The modulus value
067     * @throws CheckDigitException if an error occurs calculating the modulus
068     * for the specified code
069     */
070    @Override
071    protected int calculateModulus(String code, boolean includesCheckDigit) throws CheckDigitException {
072        StringBuilder transformed = new  StringBuilder(code.length() * 2);
073        if (includesCheckDigit) {
074            char checkDigit = code.charAt(code.length()-1); // fetch the last character
075            if (!Character.isDigit(checkDigit)){
076                throw new CheckDigitException("Invalid checkdigit["+ checkDigit+ "] in " + code);
077            }
078        }
079        for (int i = 0; i < code.length(); i++) {
080            int charValue = Character.getNumericValue(code.charAt(i));
081            if (charValue < 0 || charValue > MAX_ALPHANUMERIC_VALUE) {
082                throw new CheckDigitException("Invalid Character[" +
083                        (i + 1) + "] = '" + charValue + "'");
084            }
085             // this converts alphanumerics to two digits
086             // so there is no need to overload toInt()
087            transformed.append(charValue);
088        }
089        return super.calculateModulus(transformed.toString(), includesCheckDigit);
090    }
091
092    /**
093     * <p>Calculates the <i>weighted</i> value of a charcter in the
094     * code at a specified position.</p>
095     *
096     * <p>For Luhn (from right to left) <b>odd</b> digits are weighted
097     * with a factor of <b>one</b> and <b>even</b> digits with a factor
098     * of <b>two</b>. Weighted values &gt; 9, have 9 subtracted</p>
099     *
100     * @param charValue The numeric value of the character.
101     * @param leftPos The position of the character in the code, counting from left to right
102     * @param rightPos The positionof the character in the code, counting from right to left
103     * @return The weighted value of the character.
104     */
105    @Override
106    protected int weightedValue(int charValue, int leftPos, int rightPos) {
107        int weight = POSITION_WEIGHT[rightPos % 2];
108        int weightedValue = (charValue * weight);
109        return ModulusCheckDigit.sumDigits(weightedValue);
110    }
111}