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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  import java.io.Serializable;
20  
21  /**
22   * Abstract <b>Modulus</b> Check digit calculation/validation.
23   * <p>
24   * Provides a <i>base</i> class for building <i>modulus</i> Check
25   * Digit routines.
26   * <p>
27   * This implementation only handles <i>single-digit numeric</i> codes, such as
28   * <b>EAN-13</b>. For <i>alphanumeric</i> codes such as <b>EAN-128</b> you
29   * will need to implement/override the <code>toInt()</code> and
30   * <code>toChar()</code> methods.
31   * <p>
32   *
33   * @version $Revision: 1739357 $
34   * @since Validator 1.4
35   */
36  public abstract class ModulusCheckDigit implements CheckDigit, Serializable {
37  
38      private static final long serialVersionUID = 2948962251251528941L;
39  
40      // N.B. The modulus can be > 10 provided that the implementing class overrides toCheckDigit and toInt
41      // (for example as in ISBN10CheckDigit)
42      private final int modulus;
43  
44      /**
45       * Construct a {@link CheckDigit} routine for a specified modulus.
46       *
47       * @param modulus The modulus value to use for the check digit calculation
48       */
49      public ModulusCheckDigit(int modulus) {
50          this.modulus = modulus;
51      }
52  
53      /**
54       * Return the modulus value this check digit routine is based on.
55       *
56       * @return The modulus value this check digit routine is based on
57       */
58      public int getModulus() {
59          return modulus;
60      }
61  
62      /**
63       * Validate a modulus check digit for a code.
64       *
65       * @param code The code to validate
66       * @return <code>true</code> if the check digit is valid, otherwise
67       * <code>false</code>
68       */
69      @Override
70      public boolean isValid(String code) {
71          if (code == null || code.length() == 0) {
72              return false;
73          }
74          try {
75              int modulusResult = calculateModulus(code, true);
76              return (modulusResult == 0);
77          } catch (CheckDigitException  ex) {
78              return false;
79          }
80      }
81  
82      /**
83       * Calculate a modulus <i>Check Digit</i> for a code which does not yet have one.
84       *
85       * @param code The code for which to calculate the Check Digit; 
86       * the check digit should not be included
87       * @return The calculated Check Digit
88       * @throws CheckDigitException if an error occurs calculating the check digit
89       */
90      @Override
91      public String calculate(String code) throws CheckDigitException {
92          if (code == null || code.length() == 0) {
93              throw new CheckDigitException("Code is missing");
94          }
95          int modulusResult = calculateModulus(code, false);
96          int charValue = (modulus - modulusResult) % modulus;
97          return toCheckDigit(charValue);
98      }
99  
100     /**
101      * Calculate the modulus for a code.
102      *
103      * @param code The code to calculate the modulus for.
104      * @param includesCheckDigit Whether the code includes the Check Digit or not.
105      * @return The modulus value
106      * @throws CheckDigitException if an error occurs calculating the modulus
107      * for the specified code
108      */
109     protected int calculateModulus(String code, boolean includesCheckDigit) throws CheckDigitException {
110         int total = 0;
111         for (int i = 0; i < code.length(); i++) {
112             int lth = code.length() + (includesCheckDigit ? 0 : 1);
113             int leftPos  = i + 1;
114             int rightPos = lth - i;
115             int charValue = toInt(code.charAt(i), leftPos, rightPos);
116             total += weightedValue(charValue, leftPos, rightPos);
117         }
118         if (total == 0) {
119             throw new CheckDigitException("Invalid code, sum is zero");
120         }
121         return total % modulus;
122     }
123 
124     /**
125      * Calculates the <i>weighted</i> value of a character in the
126      * code at a specified position.
127      * <p>
128      * Some modulus routines weight the value of a character
129      * depending on its position in the code (e.g. ISBN-10), while
130      * others use different weighting factors for odd/even positions
131      * (e.g. EAN or Luhn). Implement the appropriate mechanism
132      * required by overriding this method.
133      *
134      * @param charValue The numeric value of the character
135      * @param leftPos The position of the character in the code, counting from left to right
136      * @param rightPos The positionof the character in the code, counting from right to left
137      * @return The weighted value of the character
138      * @throws CheckDigitException if an error occurs calculating
139      * the weighted value
140      */
141     protected abstract int weightedValue(int charValue, int leftPos, int rightPos)
142             throws CheckDigitException;
143 
144 
145     /**
146      * Convert a character at a specified position to an integer value.
147      * <p>
148      * <b>Note:</b> this implementation only handlers numeric values
149      * For non-numeric characters, override this method to provide
150      * character--&gt;integer conversion.
151      *
152      * @param character The character to convert
153      * @param leftPos The position of the character in the code, counting from left to right (for identifiying the position in the string)
154      * @param rightPos The position of the character in the code, counting from right to left (not used here)
155      * @return The integer value of the character
156      * @throws CheckDigitException if character is non-numeric
157      */
158     protected int toInt(char character, int leftPos, int rightPos)
159             throws CheckDigitException {
160         if (Character.isDigit(character)) {
161             return Character.getNumericValue(character);
162         }
163         throw new CheckDigitException("Invalid Character[" +
164                 leftPos + "] = '" + character + "'");
165     }
166 
167     /**
168      * Convert an integer value to a check digit.
169      * <p>
170      * <b>Note:</b> this implementation only handles single-digit numeric values
171      * For non-numeric characters, override this method to provide
172      * integer--&gt;character conversion.
173      *
174      * @param charValue The integer value of the character
175      * @return The converted character
176      * @throws CheckDigitException if integer character value
177      * doesn't represent a numeric character
178      */
179     protected String toCheckDigit(int charValue)
180             throws CheckDigitException {
181         if (charValue >= 0 && charValue <= 9) { // CHECKSTYLE IGNORE MagicNumber
182             return Integer.toString(charValue);
183         }
184         throw new CheckDigitException("Invalid Check Digit Value =" +
185                 + charValue);
186     }
187 
188     /**
189      * Add together the individual digits in a number.
190      *
191      * @param number The number whose digits are to be added
192      * @return The sum of the digits
193      */
194     public static int sumDigits(int number) {
195         int total = 0;
196         int todo = number;
197         while (todo > 0) {
198             total += todo % 10; // CHECKSTYLE IGNORE MagicNumber
199             todo  = todo / 10; // CHECKSTYLE IGNORE MagicNumber
200         }
201         return total;
202     }
203 
204 }