/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 *
 *
 * This file incorporates work covered by the following copyright and
 * permission notice:
 *
 * Copyright 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 javax.el;

import java.lang.reflect.Constructor;
import java.io.InputStream;
import java.io.File;
import java.io.FileInputStream;
import java.util.Properties;
import java.io.BufferedReader;
import java.io.InputStreamReader;

class FactoryFinder {

    /**
     * Creates an instance of the specified class using the specified 
     * <code>ClassLoader</code> object.
     *
     * @exception ELException if the given class could not be found
     *            or could not be instantiated
     */
    private static Object newInstance(String className,
                                      ClassLoader classLoader,
                                      Properties properties)
    {
        try {
            Class<?> spiClass;
            if (classLoader == null) {
                spiClass = Class.forName(className);
            } else {
                spiClass = classLoader.loadClass(className);
            }
            if (properties != null) {
                Constructor constr = null;
                try {
                    constr = spiClass.getConstructor(Properties.class);
                } catch (Exception ex) {
                }
                if (constr != null) {
                    return constr.newInstance(properties);
                }
            }
            return spiClass.newInstance();
        } catch (ClassNotFoundException x) {
            throw new ELException(
                "Provider " + className + " not found", x);
        } catch (Exception x) {
            throw new ELException(
                "Provider " + className + " could not be instantiated: " + x,
                x);
        }
    }

    /**
     * Finds the implementation <code>Class</code> object for the given
     * factory name, or if that fails, finds the <code>Class</code> object
     * for the given fallback class name. The arguments supplied must be
     * used in order. If using the first argument is successful, the second
     * one will not be used.
     * <P>
     * This method is package private so that this code can be shared.
     *
     * @return the <code>Class</code> object of the specified message factory;
     *         may not be <code>null</code>
     *
     * @param factoryId             the name of the factory to find, which is
     *                              a system property
     * @param fallbackClassName     the implementation class name, which is
     *                              to be used only if nothing else
     *                              is found; <code>null</code> to indicate that
     *                              there is no fallback class name
     * @exception ELException if there is an error
     */
    static Object find(String factoryId, String fallbackClassName,
                       Properties properties)
    {
        ClassLoader classLoader;
        try {
            classLoader = Thread.currentThread().getContextClassLoader();
        } catch (Exception x) {
            throw new ELException(x.toString(), x);
        }

        String serviceId = "META-INF/services/" + factoryId;
        // try to find services in CLASSPATH
        try {
            InputStream is=null;
            if (classLoader == null) {
                is=ClassLoader.getSystemResourceAsStream(serviceId);
            } else {
                is=classLoader.getResourceAsStream(serviceId);
            }
        
            if( is!=null ) {
                BufferedReader rd =
                    new BufferedReader(new InputStreamReader(is, "UTF-8"));
        
                String factoryClassName = rd.readLine();
                rd.close();

                if (factoryClassName != null &&
                    ! "".equals(factoryClassName)) {
                    return newInstance(factoryClassName, classLoader, properties);
                }
            }
        } catch( Exception ex ) {
        }
        

        // try to read from $java.home/lib/el.properties
        try {
            String javah=System.getProperty( "java.home" );
            String configFile = javah + File.separator +
                "lib" + File.separator + "el.properties";
            File f=new File( configFile );
            if( f.exists()) {
                Properties props=new Properties();
                props.load( new FileInputStream(f));
                String factoryClassName = props.getProperty(factoryId);
                return newInstance(factoryClassName, classLoader, properties);
            }
        } catch(Exception ex ) {
        }


        // Use the system property
        try {
            String systemProp =
                System.getProperty( factoryId );
            if( systemProp!=null) {
                return newInstance(systemProp, classLoader, properties);
            }
        } catch (SecurityException se) {
        }

        if (fallbackClassName == null) {
            throw new ELException(
                "Provider for " + factoryId + " cannot be found", null);
        }

        return newInstance(fallbackClassName, classLoader, properties);
    }
}