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
019/**
020 * Modulus 10 <strong>ISIN</strong> (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 <em>Modulus 10 Double Add Double</em> 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="https://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    /**
046     * Singleton ISIN Check Digit instance.
047     */
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    }
058
059    /**
060     * Calculate the modulus for an ISIN code.
061     *
062     * @param code               The code to calculate the modulus for.
063     * @param includesCheckDigit Whether the code includes the Check Digit or not.
064     * @return The modulus value.
065     * @throws CheckDigitException if an error occurs calculating the modulus for the specified code.
066     */
067    @Override
068    protected int calculateModulus(final String code, final boolean includesCheckDigit) throws CheckDigitException {
069        final StringBuilder transformed = new StringBuilder(code.length() * 2); // CHECKSTYLE IGNORE MagicNumber
070        if (includesCheckDigit) {
071            final char checkDigit = code.charAt(code.length() - 1); // fetch the last character
072            if (!isAsciiDigit(checkDigit)) {
073                throw new CheckDigitException("Invalid checkdigit[%c] in %s", checkDigit, code);
074            }
075        }
076        for (int i = 0; i < code.length(); i++) {
077            final char character = code.charAt(i);
078            if (!isAsciiAlphaNum(character)) {
079                throw new CheckDigitException("Invalid Character[%d] = '%c'", i + 1, character);
080            }
081            // this converts alphanumerics to two digits
082            // so there is no need to overload toInt()
083            transformed.append(Character.getNumericValue(character));
084        }
085        return super.calculateModulus(transformed.toString(), includesCheckDigit);
086    }
087
088    /**
089     * Calculates the <em>weighted</em> value of a character in the code at a specified position.
090     *
091     * <p>
092     * For ISIN (from right to left) <strong>odd</strong> digits are weighted with a factor of <strong>one</strong> and <strong>even</strong> digits with a
093     * factor of <strong>two</strong>. Weighted values are reduced to their digital root
094     * </p>
095     *
096     * @param charValue The numeric value of the character.
097     * @param leftPos   The position of the character in the code, counting from left to right.
098     * @param rightPos  The position of the character in the code, counting from right to left.
099     * @return The weighted value of the character.
100     */
101    @Override
102    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
103        final int weight = POSITION_WEIGHT[rightPos % 2]; // CHECKSTYLE IGNORE MagicNumber
104        final int weightedValue = charValue * weight;
105        return sumDigits(weightedValue);
106    }
107}