/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.log4j.helpers;

import java.net.URL;
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;
import java.io.InterruptedIOException;

/**
 * Load resources (or images) from various sources.
 * 
 * @author Ceki G&uuml;lc&uuml;
 */

public class Loader {

    static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";

    // We conservatively assume that we are running under Java 1.x
    static private boolean java1 = true;

    static private boolean ignoreTCL = false;

    static {
	String prop = OptionConverter.getSystemProperty("java.version", null);

	if (prop != null) {
	    int i = prop.indexOf('.');
	    if (i != -1) {
		if (prop.charAt(i + 1) != '1')
		    java1 = false;
	    }
	}
	String ignoreTCLProp = OptionConverter.getSystemProperty("log4j.ignoreTCL", null);
	if (ignoreTCLProp != null) {
	    ignoreTCL = OptionConverter.toBoolean(ignoreTCLProp, true);
	}
    }

    /**
     * Get a resource by delegating to getResource(String).
     * 
     * @param resource resource name
     * @param clazz    class, ignored.
     * @return URL to resource or null.
     * @deprecated as of 1.2.
     */
    public static URL getResource(String resource, Class clazz) {
	return getResource(resource);
    }

    /**
     * This method will search for <code>resource</code> in different places. The
     * search order is as follows:
     * 
     * <ol>
     * 
     * <p>
     * <li>Search for <code>resource</code> using the thread context class loader
     * under Java2. If that fails, search for <code>resource</code> using the class
     * loader that loaded this class (<code>Loader</code>). Under JDK 1.1, only the
     * the class loader that loaded this class (<code>Loader</code>) is used.
     * 
     * <p>
     * <li>Try one last time with
     * <code>ClassLoader.getSystemResource(resource)</code>, that is is using the
     * system class loader in JDK 1.2 and virtual machine's built-in class loader in
     * JDK 1.1.
     * 
     * </ol>
     */
    static public URL getResource(String resource) {
	ClassLoader classLoader = null;
	URL url = null;

	try {
	    if (!java1 && !ignoreTCL) {
		classLoader = getTCL();
		if (classLoader != null) {
		    LogLog.debug("Trying to find [" + resource + "] using context classloader " + classLoader + ".");
		    url = classLoader.getResource(resource);
		    if (url != null) {
			return url;
		    }
		}
	    }

	    // We could not find resource. Ler us now try with the
	    // classloader that loaded this class.
	    classLoader = Loader.class.getClassLoader();
	    if (classLoader != null) {
		LogLog.debug("Trying to find [" + resource + "] using " + classLoader + " class loader.");
		url = classLoader.getResource(resource);
		if (url != null) {
		    return url;
		}
	    }
	} catch (IllegalAccessException t) {
	    LogLog.warn(TSTR, t);
	} catch (InvocationTargetException t) {
	    if (t.getTargetException() instanceof InterruptedException
		    || t.getTargetException() instanceof InterruptedIOException) {
		Thread.currentThread().interrupt();
	    }
	    LogLog.warn(TSTR, t);
	} catch (Throwable t) {
	    //
	    // can't be InterruptedException or InterruptedIOException
	    // since not declared, must be error or RuntimeError.
	    LogLog.warn(TSTR, t);
	}

	// Last ditch attempt: get the resource from the class path. It
	// may be the case that clazz was loaded by the Extentsion class
	// loader which the parent of the system class loader. Hence the
	// code below.
	LogLog.debug("Trying to find [" + resource + "] using ClassLoader.getSystemResource().");
	return ClassLoader.getSystemResource(resource);
    }

    /**
     * Are we running under JDK 1.x?
     */
    public static boolean isJava1() {
	return java1;
    }

    /**
     * Get the Thread Context Loader which is a JDK 1.2 feature. If we are running
     * under JDK 1.1 or anything else goes wrong the method returns
     * <code>null<code>.
     *
     */
    private static ClassLoader getTCL() throws IllegalAccessException, InvocationTargetException {

	// Are we running on a JDK 1.2 or later system?
	Method method = null;
	try {
	    method = Thread.class.getMethod("getContextClassLoader", null);
	} catch (NoSuchMethodException e) {
	    // We are running on JDK 1.1
	    return null;
	}

	return (ClassLoader) method.invoke(Thread.currentThread(), null);
    }

    /**
     * If running under JDK 1.2 load the specified class using the
     * <code>Thread</code> <code>contextClassLoader</code> if that fails try
     * Class.forname. Under JDK 1.1 only Class.forName is used.
     *
     */
    static public Class loadClass(String clazz) throws ClassNotFoundException {
	// Just call Class.forName(clazz) if we are running under JDK 1.1
	// or if we are instructed to ignore the TCL.
	if (java1 || ignoreTCL) {
	    return Class.forName(clazz);
	} else {
	    try {
		return getTCL().loadClass(clazz);
	    }
	    // we reached here because tcl was null or because of a
	    // security exception, or because clazz could not be loaded...
	    // In any case we now try one more time
	    catch (InvocationTargetException e) {
		if (e.getTargetException() instanceof InterruptedException
			|| e.getTargetException() instanceof InterruptedIOException) {
		    Thread.currentThread().interrupt();
		}
	    } catch (Throwable t) {
	    }
	}
	return Class.forName(clazz);
    }
}
