// Copyright 2006 Daniel Gredler

 //

 // Licensed 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 net.sf.beanform.util;

 import java.util.HashMap;

 import java.util.Map;

 /**

  * A thread-safe cache of strings that allows aliasing of long strings to smaller

  * strings that can then be used to reverse the process.

  *

  * @author Daniel Gredler

  */

 public class StringCache {

     protected final static char[] CHARS = {

         'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',

         'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',

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

     protected int maxSize;

     protected Map<String, String> cacheByShort;

     protected Map<String, String> cacheByReal;

     public StringCache( int maxSize ) {

         this.maxSize = maxSize;

         this.cacheByShort = new HashMap<String, String>( maxSize );

         this.cacheByReal = new HashMap<String, String>( maxSize );

     }

     public synchronized String getShortVersion( String real ) {

         if( this.cacheByReal.size() == this.maxSize ) return real;

         String s;

         if( this.cacheByReal.containsKey( real ) ) {

             s = this.cacheByReal.get( real );

         }

         else {

             s = Character.toString( CHARS[ 0 ] );

             for( int i = 1; this.cacheByShort.containsKey( s ); i++ ) {

                 s = getChars( CHARS, i );

             }

             this.cacheByShort.put( s, real );

             this.cacheByReal.put( real, s );

         }

         return s;

     }

     public synchronized String getRealVersion( String shortVersion ) {

         String real;

         if( this.cacheByShort.containsKey( shortVersion ) ) {

             real = this.cacheByShort.get( shortVersion );

         }

         else {

             real = shortVersion;

         }

         return real;

     }

     protected static String getChars( char[] chars, int index ) {

         String s = new String();

         int i = index / chars.length;

         if( i > 0 ) {

             s = getChars( chars, i - 1 ) + s;

         }

         s = s + chars[ index % chars.length ];

         return s;

     }

 }