/* XMLEntityResolver.java                                          NanoXML/Java
 *
 * $Revision: 1.4 $
 * $Date: 2002/01/04 21:03:29 $
 * $Name: RELEASE_2_2_1 $
 *
 * This file is part of NanoXML 2 for Java.
 * Copyright (C) 2000-2002 Marc De Scheemaecker, All Rights Reserved.
 *
 * This software is provided 'as-is', without any express or implied warranty.
 * In no event will the authors be held liable for any damages arising from the
 * use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 *  1. The origin of this software must not be misrepresented; you must not
 *     claim that you wrote the original software. If you use this software in
 *     a product, an acknowledgment in the product documentation would be
 *     appreciated but is not required.
 *
 *  2. Altered source versions must be plainly marked as such, and must not be
 *     misrepresented as being the original software.
 *
 *  3. This notice may not be removed or altered from any source distribution.
 */

package net.n3.nanoxml;


import java.util.Hashtable;
import java.io.Reader;
import java.io.StringReader;


/**
 * An XMLEntityResolver resolves entities.
 *
 * @author Marc De Scheemaecker
 * @version $Name: RELEASE_2_2_1 $, $Revision: 1.4 $
 */
public class XMLEntityResolver
   implements IXMLEntityResolver
{

   /**
    * The entities.
    */
   private Hashtable entities;


   /**
    * Initializes the resolver.
    */
   public XMLEntityResolver()
   {
      this.entities = new Hashtable();
      this.entities.put("amp", "&#38;");
      this.entities.put("quot", "&#34;");
      this.entities.put("apos", "&#39;");
      this.entities.put("lt", "&#60;");
      this.entities.put("gt", "&#62;");
   }


   /**
    * Cleans up the object when it's destroyed.
    */
   protected void finalize()
      throws Throwable
   {
      this.entities.clear();
      this.entities = null;
      super.finalize();
   }


   /**
    * Adds an internal entity.
    *
    * @param name the name of the entity.
    * @param value the value of the entity.
    */
   public void addInternalEntity(String name,
                                 String value)
   {
      if (! this.entities.containsKey(name)) {
         this.entities.put(name, value);
      }
   }


   /**
    * Adds an external entity.
    *
    * @param name the name of the entity.
    * @param publicID the public ID of the entity, which may be null.
    * @param systemID the system ID of the entity.
    */
   public void addExternalEntity(String name,
                                 String publicID,
                                 String systemID)
   {
      if (! this.entities.containsKey(name)) {
         this.entities.put(name, new String[] { publicID, systemID } );
      }
   }


   /**
    * Returns a Java reader containing the value of an entity.
    *
    * @param xmlReader the current XML reader
    * @param name the name of the entity.
    *
    * @return the reader, or null if the entity could not be resolved.
    */
   public Reader getEntity(IXMLReader xmlReader,
                           String     name)
      throws XMLParseException
   {
      Object obj = this.entities.get(name);

      if (obj == null) {
         return null;
      } else if (obj instanceof java.lang.String) {
         return new StringReader((String)obj);
      } else {
         String[] id = (String[]) obj;
         return this.openExternalEntity(xmlReader, id[0], id[1]);
      }
   }


   /**
    * Returns true if an entity is external.
    *
    * @param name the name of the entity.
    */
   public boolean isExternalEntity(String name)
   {
      Object obj = this.entities.get(name);
      return ! (obj instanceof java.lang.String);
   }


   /**
    * Opens an external entity.
    *
    * @param xmlReader the current XML reader
    * @param publicID the public ID, which may be null
    * @param systemID the system ID
    *
    * @return the reader, or null if the reader could not be created/opened
    */
   protected Reader openExternalEntity(IXMLReader xmlReader,
                                       String     publicID,
                                       String     systemID)
      throws XMLParseException
   {
      String parentSystemID = xmlReader.getSystemID();

      try {
         return xmlReader.openStream(publicID, systemID);
      } catch (Exception e) {
         throw new XMLParseException(parentSystemID,
                                     xmlReader.getLineNr(),
                                     "Could not open external entity "
                                     + "at system ID: " + systemID);
      }
   }

}
