/*

  * Copyright 1999,2004 The Apache Software Foundation.

  * 

  * 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 org.apache.commons.feedparser.locate;

 import java.util.HashMap;

 import java.util.regex.Matcher;

 import java.util.regex.Pattern;

 /**

  *

  * Given a string of HTML content we decode the entities it contains.

  *

  * NOTE: Currently this is a trivial implementation and we need to go through

  * and make sure all HTML entities are correctly supported.

  * 

  * @author <a href="mailto:burton@openprivacy.org">Kevin A. Burton</a>

  * @version $Id: EntityDecoder.java 373622 2006-01-30 22:53:00Z mvdb $

  */

 public class EntityDecoder {

     //FIXME: see FeedFilter.java for a list of all valid HTML entities.  I

     //should replace them with character literals in this situation.

     private static HashMap entities = new HashMap();

     static Pattern pattern = Pattern.compile( "&([a-z]+);" );

     static {

         //FIXME: there are a LOT more of these and we need an exhaustive colleciton.

         entities.put( "gt", ">" );

         entities.put( "apos", ">" );

         entities.put( "lt", "<" );

         entities.put( "amp", "&" );

         //FIXME: 

         entities.put( "raquo", "" );

         entities.put( "laquo", "" );

     }

     /**

      * Decode content.  If a null is passed in we return null. 

      *

      * 

      */

     public static String decode( String content ) {

         if ( content == null )

             return null;

         //FIXME(performance): do I have existing code that does this more efficiently?

         if (content == null)

             return null;

         StringBuffer buff = new StringBuffer( content.length() );

         Matcher m = pattern.matcher( content );

         int index = 0;

         while ( m.find() ) {

             //figure out which entity to escape or just include it.

             buff.append( content.substring( index, m.start( 0 ) ) );

             String entity = m.group( 1 );

             if ( entities.containsKey( entity ) ) {

                 buff.append( entities.get( entity ) );

             } else {

                 //found an entity we no NOTHING about.  Should we warn?

                 buff.append( m.group( 0 ) );

             }

             index = m.end( 0 );

         }

         buff.append( content.substring( index, content.length() ) );

         return buff.toString();

     }

     public static void main( String[] args ) throws Exception {

         System.out.println( decode( "&" ) );

         System.out.println( decode( "asdf&asdf" ) );

         System.out.println( decode( "asdf&" ) );

         System.out.println( decode( "&asdf" ) );

     }

 }