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}