/*
 * 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.
 */
/*
 * $Id: FuncLoader.java,v 1.10 2004/02/23 10:29:37 aruny Exp $
 */
package com.sun.org.apache.xpath.internal.compiler;

import javax.xml.transform.TransformerException;

import com.sun.org.apache.xpath.internal.functions.Function;

/**
 * Lazy load of functions into the function table as needed, so we don't 
 * have to load all the functions allowed in XPath and XSLT on startup.
 * @xsl.usage advanced
 */
public class FuncLoader
{

  /** The function ID, which may correspond to one of the FUNC_XXX values 
   *  found in {@link com.sun.org.apache.xpath.internal.compiler.FunctionTable}, but may 
   *  be a value installed by an external module.  */
  private int m_funcID;

  /** The class name of the function.  Must not be null.   */
  private String m_funcName;

  /**
   * Get the local class name of the function class.  If function name does 
   * not have a '.' in it, it is assumed to be relative to 
   * 'com.sun.org.apache.xpath.internal.functions'.
   *
   * @return The class name of the {com.sun.org.apache.xpath.internal.functions.Function} class.
   */
  public String getName()
  {
    return m_funcName;
  }

  /**
   * Construct a function loader
   *
   * @param funcName The class name of the {com.sun.org.apache.xpath.internal.functions.Function} 
   *             class, which, if it does not have a '.' in it, is assumed to 
   *             be relative to 'com.sun.org.apache.xpath.internal.functions'. 
   * @param funcID  The function ID, which may correspond to one of the FUNC_XXX 
   *    values found in {@link com.sun.org.apache.xpath.internal.compiler.FunctionTable}, but may 
   *    be a value installed by an external module. 
   */
  public FuncLoader(String funcName, int funcID)
  {

    super();

    m_funcID = funcID;
    m_funcName = funcName;
  }

  /**
   * Get a Function instance that this instance is liaisoning for.
   *
   * @return non-null reference to Function derivative.
   *
   * @throws javax.xml.transform.TransformerException if ClassNotFoundException, 
   *    IllegalAccessException, or InstantiationException is thrown.
   */
  Function getFunction() throws TransformerException
  {
    try
    {
      String className = m_funcName;
      if (className.indexOf(".") < 0) {
        className = "com.sun.org.apache.xpath.internal.functions." + className;
      }
      //hack for loading only built-in function classes.
      Function func = (Function) ObjectFactory.newInstance(
          className, ObjectFactory.findClassLoader(), true);
      //Sun's implementation use null to represent the bootstrap class loader.
      if(func.getClass().getClassLoader() == null)
          return func;
      else
          throw new TransformerException("Application can't install his own xpath function.");
    }
    catch (ObjectFactory.ConfigurationError e)
    {
      throw new TransformerException(e.getException());
    }
  }
}