/*
 * ImplementationSource.java
 * Copyright (C) 2004 The Free Software Foundation, Inc.
 * 
 * This file is part of GNU JAXP, a library.
 *
 * GNU JAXP is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * GNU JAXP is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Linking this library statically or dynamically with other modules is
 * making a combined work based on this library.  Thus, the terms and
 * conditions of the GNU General Public License cover the whole
 * combination.
 *
 * As a special exception, the copyright holders of this library give you
 * permission to link this library with independent modules to produce an
 * executable, regardless of the license terms of these independent
 * modules, and to copy and distribute the resulting executable under
 * terms of your choice, provided that you also meet, for each linked
 * independent module, the terms and conditions of the license of that
 * module.  An independent module is a module which is not derived from
 * or based on this library.  If you modify this library, you may extend
 * this exception to your version of the library, but you are not
 * obliged to do so.  If you do not wish to do so, delete this
 * exception statement from your version. 
 */
package gnu.xml.dom;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

import org.w3c.dom.DOMImplementation;
import org.w3c.dom.DOMImplementationList;
import org.w3c.dom.DOMImplementationSource;

/**
 * Implementation source for GNU JAXP.
 *
 * @author <a href='mailto:dog@gnu.org'>Chris Burdess</a>
 */
public class ImplementationSource
  implements DOMImplementationSource
{

  private static final String DIGITS = "1234567890";

  /*
   * GNU DOM implementations.
   */
  private static final DOMImplementation[] implementations;

  static
  {
    List acc = new ArrayList();
    acc.add(new gnu.xml.dom.DomImpl());
    try
      {
        Class t = Class.forName("gnu.xml.libxmlj.dom.GnomeDocumentBuilder");
        acc.add(t.newInstance());
      }
    catch (Exception e)
      {
        // libxmlj not available        
      }
    catch (UnsatisfiedLinkError e)
      {
        // libxmlj not available
      }
    implementations = new DOMImplementation[acc.size()];
    acc.toArray(implementations);
  }

  public DOMImplementation getDOMImplementation(String features)
  {
    List available = getImplementations(features);
    if (available.isEmpty())
      {
        return null;
      }
    return (DOMImplementation) available.get(0);
  }

  public DOMImplementationList getDOMImplementationList(String features)
  {
    List available = getImplementations(features);
    return new ImplementationList(available);
  }

  /**
   * Returns a list of the implementations that support the specified
   * features.
   */
  private final List getImplementations(String features)
  {
    List available = new ArrayList(Arrays.asList(implementations));
    for (Iterator i = parseFeatures(features).iterator(); i.hasNext(); )
      {
        String feature = (String) i.next();
        String version = null;
        int si = feature.indexOf(' ');
        if (si != -1)
          {
            version = feature.substring(si + 1);
            feature = feature.substring(0, si);
          }
        for (Iterator j = available.iterator(); j.hasNext(); )
          {
            DOMImplementation impl = (DOMImplementation) j.next();
            if (!impl.hasFeature(feature, version))
              {
                j.remove();
              }
          }
      }
    return available;
  }

  /**
   * Parses the feature list into feature tokens.
   */
  final List parseFeatures(String features)
  {
    List list = new ArrayList();
    int pos = 0, start = 0;
    int len = features.length();
    for (; pos < len; pos++)
      {
        char c = features.charAt(pos);
        if (c == ' ')
          {
            if (pos + 1 < len &&
                DIGITS.indexOf(features.charAt(pos + 1)) == -1)
              {
                list.add(getFeature(features, start, pos));
                start = pos + 1;
              }
          }
      }
    if (pos > start)
      {
        list.add(getFeature(features, start, len));
      }
    return list;
  }

  final String getFeature(String features, int start, int end)
  {
    if (features.length() > 0 && features.charAt(start) == '+')
      {
        return features.substring(start + 1, end);
      }
    return features.substring(start, end);
  }

}
