/*

  * Licensed to the Apache Software Foundation (ASF) under one or more

  * contributor license agreements.  See the NOTICE file distributed with

  * this work for additional information regarding copyright ownership.

  * The ASF licenses this file to You under the Apache License, Version 2.0

  * (the "License"); you may not use this file except in compliance with

  * the License.  You may obtain a copy of the License at

  *

  *      http://www.apache.org/licenses/LICENSE-2.0

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.apache.commons.validator.routines.checkdigit;

 import java.io.Serializable;

 /**

  * <b>Verhoeff</b> (Dihedral) Check Digit calculation/validation.

  * <p>

  * Check digit calculation for numeric codes using a

  * <a href="http://en.wikipedia.org/wiki/Dihedral_group">Dihedral Group</a>

  * of order 10.

  * <p>

  * See <a href="http://en.wikipedia.org/wiki/Verhoeff_algorithm">Wikipedia

  *  - Verhoeff algorithm</a> for more details.

  *

  * @version $Revision: 1739357 $

  * @since Validator 1.4

  */

 public final class VerhoeffCheckDigit implements CheckDigit, Serializable {

     private static final long serialVersionUID = 4138993995483695178L;

     /** Singleton Verhoeff Check Digit instance */

     public static final CheckDigit VERHOEFF_CHECK_DIGIT = new VerhoeffCheckDigit();

     /** D - multiplication table */

     private static final int[][] D_TABLE = new int[][] {

         {0,  1,  2,  3,  4,  5,  6,  7,  8,  9},

         {1,  2,  3,  4,  0,  6,  7,  8,  9,  5},

         {2,  3,  4,  0,  1,  7,  8,  9,  5,  6},

         {3,  4,  0,  1,  2,  8,  9,  5,  6,  7},

         {4,  0,  1,  2,  3,  9,  5,  6,  7,  8},

         {5,  9,  8,  7,  6,  0,  4,  3,  2,  1},

         {6,  5,  9,  8,  7,  1,  0,  4,  3,  2},

         {7,  6,  5,  9,  8,  2,  1,  0,  4,  3},

         {8,  7,  6,  5,  9,  3,  2,  1,  0,  4},

         {9,  8,  7,  6,  5,  4,  3,  2,  1,  0}};

     /** P - permutation table */

     private static final int[][] P_TABLE = new int[][] {

         {0,  1,  2,  3,  4,  5,  6,  7,  8,  9},

         {1,  5,  7,  6,  2,  8,  3,  0,  9,  4},

         {5,  8,  0,  3,  7,  9,  6,  1,  4,  2},

         {8,  9,  1,  6,  0,  4,  3,  5,  2,  7},

         {9,  4,  5,  3,  1,  2,  6,  8,  7,  0},

         {4,  2,  8,  6,  5,  7,  3,  9,  0,  1},

         {2,  7,  9,  3,  8,  0,  6,  4,  1,  5},

         {7,  0,  4,  6,  9,  1,  3,  2,  5,  8}};

     /** inv: inverse table */

     private static final int[] INV_TABLE = new int[]

         {0,  4,  3,  2,  1,  5,  6,  7,  8,  9};

     /**

      * Validate the Verhoeff <i>Check Digit</i> for a code.

      *

      * @param code The code to validate

      * @return <code>true</code> if the check digit is valid,

      * otherwise <code>false</code>

      */

     @Override

     public boolean isValid(String code) {

         if (code == null || code.length() == 0) {

             return false;

         }

         try {

             return (calculateChecksum(code, true) == 0);

         } catch (CheckDigitException e) {

             return false;

         }

     }

     /**

      * Calculate a Verhoeff <i>Check Digit</i> for a code.

      *

      * @param code The code to calculate the Check Digit for

      * @return The calculated Check Digit

      * @throws CheckDigitException if an error occurs calculating

      * the check digit for the specified code

      */

     @Override

     public String calculate(String code) throws CheckDigitException {

         if (code == null || code.length() == 0) {

             throw new CheckDigitException("Code is missing");

         }

         int checksum = calculateChecksum(code, false);

         return Integer.toString(INV_TABLE[checksum]);

     }

     /**

      * Calculate the checksum.

      *

      * @param code The code to calculate the checksum for.

      * @param includesCheckDigit Whether the code includes the Check Digit or not.

      * @return The checksum value

      * @throws CheckDigitException if the code contains an invalid character (i.e. not numeric)

      */

     private int calculateChecksum(String code, boolean includesCheckDigit) throws CheckDigitException {

         int checksum = 0;

         for (int i = 0; i < code.length(); i++) {

             int idx = code.length() - (i + 1);

             int num = Character.getNumericValue(code.charAt(idx));

             if (num < 0 || num > 9) { // CHECKSTYLE IGNORE MagicNumber

                 throw new CheckDigitException("Invalid Character[" +

                         i + "] = '" + ((int)code.charAt(idx)) + "'");

             }

             int pos = includesCheckDigit ? i : i + 1;

             checksum = D_TABLE[checksum][P_TABLE[pos % 8][num]]; // CHECKSTYLE IGNORE MagicNumber

         }

         return checksum;

     }

 }