/*
 * XPathFactory.java
 * Copyright (C) 2004 The Free Software Foundation
 * 
 * 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 javax.xml.xpath;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.Properties;

/**
 * Factory for creating XPath environments.
 *
 * @author <a href='mailto:dog@gnu.org'>Chris Burdess</a>
 * @since 1.3
 */
public abstract class XPathFactory
{

  /**
   * The default property name according to the JAXP specification.
   */
  public static final String DEFAULT_PROPERTY_NAME =
	 	"javax.xml.xpath.XPathFactory";

  /**
   * The default object model URI.
   */
  public static final String DEFAULT_OBJECT_MODEL_URI =
    XPathConstants.DOM_OBJECT_MODEL;

  protected XPathFactory()
  {
  }

  /**
   * Returns a new factory for the default (DOM) object model.
   */
  public static final XPathFactory newInstance()
  {
    try
      {
        return newInstance(DEFAULT_OBJECT_MODEL_URI);
      }
    catch (XPathFactoryConfigurationException e)
      {
        throw new RuntimeException(e.getMessage());
      }
  }

  /**
   * Returns a new factory for the given object model URI.
   * The implementation class to load is the first found in the following
   * locations that advertises support for the given model URI:
   * <ol>
   * <li>the <code>javax.xml.xpath.XPathFactory</code> system property</li>
   * <li>the above named property value in the
   * <code><i>$JAVA_HOME</i>/lib/jaxp.properties</code> file</li>
   * <li>the class name specified in the
   * <code>META-INF/services/javax.xml.xpath.XPathFactory</code> system
   * resource</li>
   * <li>the default factory class</li>
   * </ol>
   * @param uri the object model URI
   */
  public static final XPathFactory newInstance(String uri)
    throws XPathFactoryConfigurationException
  {
    ClassLoader loader = Thread.currentThread().getContextClassLoader();
    if (loader == null)
      {
        loader = XPathFactory.class.getClassLoader();
      }
    String className = null;
    int count = 0;
    do
      {
        className = getFactoryClassName(loader, count++);
        if (className != null)
          {
            try
              {
                Class t = (loader != null) ? loader.loadClass(className) :
                  Class.forName(className);
                XPathFactory ret = (XPathFactory) t.newInstance();
                if (ret.isObjectModelSupported(uri))
                  {
                    return ret;
                  }
                className = null;
              }
            catch (ClassNotFoundException e)
              {
                className = null;
              }
            catch (Exception e)
              {
                throw new XPathFactoryConfigurationException(e);
              }
          }
      }
    while (className == null && count < 4);
    String msg = "no factories with support for " + uri;
    throw new XPathFactoryConfigurationException(msg);
  }

  private static String getFactoryClassName(ClassLoader loader, int attempt)
  {
    final String propertyName = DEFAULT_PROPERTY_NAME;
    switch (attempt)
      {
        case 0:
          return System.getProperty(propertyName);
        case 1:
          try
            {
              File file = new File(System.getProperty("java.home"));
              file = new File(file, "lib");
              file = new File(file, "jaxp.properties");
              InputStream in = new FileInputStream(file);
              Properties props = new Properties();
              props.load(in);
              in.close();
              return props.getProperty(propertyName);
            }
          catch (IOException e)
            {
              return null;
            }
        case 2:
          try
            {
              String serviceKey = "/META-INF/services/" + propertyName;
              InputStream in = (loader != null) ?
                loader.getResourceAsStream(serviceKey) :
                XPathFactory.class.getResourceAsStream(serviceKey);
              if (in != null)
                {
                  BufferedReader r =
                    new BufferedReader(new InputStreamReader(in));
                  String ret = r.readLine();
                  r.close();
                  return ret;
                }
            }
          catch (IOException e)
            {
            }
          return null;
        case 3:
          return "gnu.xml.xpath.XPathFactoryImpl";
        default:
          return null;
      }
  }

  /**
   * Indicates whether the specified object model URI is supported by
   * this factory.
   */
  public abstract boolean isObjectModelSupported(String objectModel);

  /**
   * Sets the state of the named feature.
   */
  public abstract void setFeature(String name, boolean value)
    throws XPathFactoryConfigurationException;

  /**
   * Returns the state of the named feature.
   */
  public abstract boolean getFeature(String name)
    throws XPathFactoryConfigurationException;

  /**
   * Sets the XPath variable resolver calback.
   */
  public abstract void setXPathVariableResolver(XPathVariableResolver resolver);

  /**
   * Sets the XPath extension function resolver calback.
   */
  public abstract void setXPathFunctionResolver(XPathFunctionResolver resolver);

  /**
   * Returns a new XPath evaluation environment.
   */
  public abstract XPath newXPath();
  
}
