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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.validator.routines.checkdigit;
18  
19  /**
20   * Modulus 10 <b>ISIN</b> (International Securities Identifying Number) Check Digit calculation/validation.
21   *
22   * <p>
23   * ISIN Numbers are 12 character alphanumeric codes used
24   * to identify Securities.
25   * </p>
26   *
27   * <p>
28   * Check digit calculation uses the <i>Modulus 10 Double Add Double</i> technique
29   * with every second digit being weighted by 2. Alphabetic characters are
30   * converted to numbers by their position in the alphabet starting with A being 10.
31   * Weighted numbers greater than ten are treated as two separate numbers.
32   * </p>
33   *
34   * <p>
35   * See <a href="http://en.wikipedia.org/wiki/ISIN">Wikipedia - ISIN</a>
36   * for more details.
37   * </p>
38   *
39   * @since 1.4
40   */
41  public final class ISINCheckDigit extends ModulusCheckDigit {
42  
43      private static final long serialVersionUID = -1239211208101323599L;
44  
45      private static final int MAX_ALPHANUMERIC_VALUE = 35; // Character.getNumericValue('Z')
46  
47      /** Singleton ISIN Check Digit instance */
48      public static final CheckDigit ISIN_CHECK_DIGIT = new ISINCheckDigit();
49  
50      /** weighting given to digits depending on their right position */
51      private static final int[] POSITION_WEIGHT = {2, 1};
52  
53      /**
54       * Constructs an ISIN Identifier Check Digit routine.
55       */
56      public ISINCheckDigit() {
57          super();
58      }
59  
60      /**
61       * Calculate the modulus for an ISIN code.
62       *
63       * @param code The code to calculate the modulus for.
64       * @param includesCheckDigit Whether the code includes the Check Digit or not.
65       * @return The modulus value
66       * @throws CheckDigitException if an error occurs calculating the modulus
67       * for the specified code
68       */
69      @Override
70      protected int calculateModulus(final String code, final boolean includesCheckDigit) throws CheckDigitException {
71          final StringBuilder transformed = new StringBuilder(code.length() * 2); // CHECKSTYLE IGNORE MagicNumber
72          if (includesCheckDigit) {
73              final char checkDigit = code.charAt(code.length() - 1); // fetch the last character
74              if (!Character.isDigit(checkDigit)) {
75                  throw new CheckDigitException("Invalid checkdigit[" + checkDigit + "] in " + code);
76              }
77          }
78          for (int i = 0; i < code.length(); i++) {
79              final int charValue = Character.getNumericValue(code.charAt(i));
80              if (charValue < 0 || charValue > MAX_ALPHANUMERIC_VALUE) {
81                  throw new CheckDigitException("Invalid Character[" + (i + 1) + "] = '" + charValue + "'");
82              }
83              // this converts alphanumerics to two digits
84              // so there is no need to overload toInt()
85              transformed.append(charValue);
86          }
87          return super.calculateModulus(transformed.toString(), includesCheckDigit);
88      }
89  
90      /**
91       * <p>Calculates the <i>weighted</i> value of a character in the
92       * code at a specified position.</p>
93       *
94       * <p>For ISIN (from right to left) <b>odd</b> digits are weighted
95       * with a factor of <b>one</b> and <b>even</b> digits with a factor
96       * of <b>two</b>. Weighted values are reduced to their digital root</p>
97       *
98       * @param charValue The numeric value of the character.
99       * @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 }