/*

  * 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;

 import java.io.Serializable;

 import org.apache.commons.validator.routines.checkdigit.CheckDigitException;

 import org.apache.commons.validator.routines.checkdigit.EAN13CheckDigit;

 import org.apache.commons.validator.routines.checkdigit.ISSNCheckDigit;

 /**

  * International Standard Serial Number (ISSN)

  * is an eight-digit serial number used to

  * uniquely identify a serial publication.

  * <pre>

  * The format is:

  * 

  * ISSN dddd-dddC

  * where:

  * d = decimal digit (0-9)

  * C = checksum (0-9 or X)

  * 

  * The checksum is formed by adding the first 7 digits multiplied by

  * the position in the entire number (counting from the right).

  * 

  * For example, abcd-efg would be 8a + 7b + 6c + 5d + 4e +3f +2g.

  * The check digit is modulus 11, where the value 10 is represented by 'X'

  * For example:

  * ISSN 0317-8471

  * ISSN 1050-124X

  *

  * This class strips off the 'ISSN ' prefix if it is present before passing

  * the remainder to the checksum routine.

  * 

  * </pre>

  * <p>

  * Note: the {@link #isValid(String)} and {@link #validate(String)} methods strip off any leading

  * or trailing spaces before doing the validation.

  * To ensure that only a valid code (without 'ISSN ' prefix) is passed to a method,

  * use the following code:

  * <pre>

  * Object valid = validator.validate(input); 

  * if (valid != null) {

  *    some_method(valid.toString());

  * }

  * </pre>

  * @since 1.5.0

  */

 public class ISSNValidator implements Serializable {

     private static final long serialVersionUID = 4319515687976420405L;

     private static final String ISSN_REGEX = "(?:ISSN )?(\\d{4})-(\\d{3}[0-9X])$"; // We don't include the '-' in the code, so it is 8 chars

     private static final CodeValidator VALIDATOR = new CodeValidator(ISSN_REGEX, 8, ISSNCheckDigit.ISSN_CHECK_DIGIT);

     /** ISSN Code Validator */

     private static final ISSNValidator ISSN_VALIDATOR = new ISSNValidator();

     /**

      * Return a singleton instance of the ISSN validator

      *

      * @return A singleton instance of the ISSN validator.

      */

     public static ISSNValidator getInstance() {

         return ISSN_VALIDATOR;

     }

     /**

      * Check the code is a valid ISSN code after any transformation

      * by the validate routine.

      * @param code The code to validate.

      * @return <code>true</code> if a valid ISSN

      * code, otherwise <code>false</code>.

      */

     public boolean isValid(String code) {

         return VALIDATOR.isValid(code);

     }

     /**

      * Check the code is valid ISSN code.

      * <p>

      * If valid, this method returns the ISSN code with

      * the 'ISSN ' prefix removed (if it was present)

      *

      * @param code The code to validate.

      * @return A valid ISSN code if valid, otherwise <code>null</code>.

      */

     public Object validate(String code) {

         return VALIDATOR.validate(code);

     }

     /**

      * Convert an ISSN code to an EAN-13 code.

      * <p>

      * This method requires a valid ISSN code.

      * It may contain a leading 'ISSN ' prefix,

      * as the input is passed through the {@link #validate(String)}

      * method.

      *

      * @param issn The ISSN code to convert

      * @param suffix the two digit suffix, e.g. "00" 

      * @return A converted EAN-13 code or <code>null</code>

      * if the input ISSN code is not valid

      */

     public String convertToEAN13(String issn, String suffix) {

         if (suffix == null || !suffix.matches("\\d\\d")) {

             throw new IllegalArgumentException("Suffix must be two digits: '" + suffix + "'");            

         }

         Object result = validate(issn);

         if (result == null) {

             return null;

         }

         // Calculate the new EAN-13 code

         final String input = result.toString();

         String ean13 = "977" + input.substring(0, input.length() -1) + suffix;

         try {

             String checkDigit = EAN13CheckDigit.EAN13_CHECK_DIGIT.calculate(ean13);

             ean13 += checkDigit;

             return ean13;

         } catch (CheckDigitException e) { // Should not happen

             throw new IllegalArgumentException("Check digit error for '" + ean13 + "' - " + e.getMessage());

         }

     }

 }