    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 * @since 1.4
    040 */
    041public final class ISINCheckDigit extends ModulusCheckDigit {
    042
    043    private static final long serialVersionUID = -1239211208101323599L;
    044
    045    private static final int MAX_ALPHANUMERIC_VALUE = 35; // Character.getNumericValue('Z')
    046
    047    /** Singleton ISIN Check Digit instance */
    048    public static final CheckDigit ISIN_CHECK_DIGIT = new ISINCheckDigit();
    049
    050    /** weighting given to digits depending on their right position */
    051    private static final int[] POSITION_WEIGHT = {2, 1};
    052
    053    /**
    054     * Constructs an ISIN Identifier Check Digit routine.
    055     */
    056    public ISINCheckDigit() {
    057        super();
    058    }
    059
    060    /**
    061     * Calculate the modulus for an ISIN code.
    062     *
    063     * @param code The code to calculate the modulus for.
    064     * @param includesCheckDigit Whether the code includes the Check Digit or not.
    065     * @return The modulus value
    066     * @throws CheckDigitException if an error occurs calculating the modulus
    067     * for the specified code
    068     */
    069    @Override
    070    protected int calculateModulus(final String code, final boolean includesCheckDigit) throws CheckDigitException {
    071        final StringBuilder transformed = new StringBuilder(code.length() * 2); // CHECKSTYLE IGNORE MagicNumber
    072        if (includesCheckDigit) {
    073            final char checkDigit = code.charAt(code.length() - 1); // fetch the last character
    074            if (!Character.isDigit(checkDigit)) {
    075                throw new CheckDigitException("Invalid checkdigit[" + checkDigit + "] in " + code);
    076            }
    077        }
    078        for (int i = 0; i < code.length(); i++) {
    079            final int charValue = Character.getNumericValue(code.charAt(i));
    080            if (charValue < 0 || charValue > MAX_ALPHANUMERIC_VALUE) {
    081                throw new CheckDigitException("Invalid Character[" + (i + 1) + "] = '" + charValue + "'");
    082            }
    083            // this converts alphanumerics to two digits
    084            // so there is no need to overload toInt()
    085            transformed.append(charValue);
    086        }
    087        return super.calculateModulus(transformed.toString(), includesCheckDigit);
    088    }
    089
    090    /**
    091     * <p>Calculates the <i>weighted</i> value of a character in the
    092     * code at a specified position.</p>
    093     *
    094     * <p>For ISIN (from right to left) <b>odd</b> digits are weighted
    095     * with a factor of <b>one</b> and <b>even</b> digits with a factor
    096     * of <b>two</b>. Weighted values are reduced to their digital root</p>
    097     *
    098     * @param charValue The numeric value of the character.
    099     * @param leftPos  The position of the character in the code, counting from left to right
    100     * @param rightPos The position of the character in the code, counting from right to left
    101     * @return The weighted value of the character.
    102     */
    103    @Override
    104    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
    105        final int weight = POSITION_WEIGHT[rightPos % 2]; // CHECKSTYLE IGNORE MagicNumber
    106        final int weightedValue = charValue * weight;
    107        return ModulusCheckDigit.sumDigits(weightedValue);
    108    }
    109}