/**
 * Copyright (c) 2011, The University of Southampton and the individual contributors.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *   *  Redistributions of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 *
 *   *  Redistributions in binary form must reproduce the above copyright notice,
 *      this list of conditions and the following disclaimer in the documentation
 *      and/or other materials provided with the distribution.
 *
 *   *  Neither the name of the University of Southampton nor the names of its
 *      contributors may be used to endorse or promote products derived from this
 *      software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.openimaj.aop.classloader;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;
import java.util.jar.Attributes;
import java.util.jar.JarFile;
import java.util.jar.Manifest;

import javassist.ClassPool;
import javassist.Loader;

import org.openimaj.aop.ClassTransformer;
import org.openimaj.aop.MultiTransformClassFileTransformer;

/**
 * {@link ClassLoaderTransform} provides an alternative to using a java agent to
 * perform byte-code manipulation by providing a classloader that will
 * automatically transform classes as they are loaded.
 * 
 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
 * 
 */
public class ClassLoaderTransform {
        /**
         * Manifest property key for specifying the actual main class when using the
         * loading technique provided by {@link #main(String[])}.
         */
        public static final String MAIN_CLASS = "OpenIMAJ-Main-Class";

        /**
         * Manifest property key for specifying the {@link ClassTransformer} classes
         * when using the loading technique provided by {@link #main(String[])}.
         */
        public static final String TRANSFORMERS = "OpenIMAJ-Transformers";

        /**
         * Separator character for separating multiple {@link ClassTransformer}s
         * when using the loading technique provided by {@link #main(String[])}.
         */
        public static final String TRANSFORMERS_SEPARATOR = ",";

        /**
         * Run the main method of the given jar file, passing all classes as they
         * are loaded through the transformer to modify the bytecode. The main
         * method must be specified by the "Main-Class" manifest entry.
         * 
         * @param pool
         *            the classpool to hold classes as they are loaded
         * @param tf
         *            the transform(s) to apply
         * @param jarFile
         *            the jar file to run
         * @param args
         *            the arguments to pass to the main method
         * @return the classloader used for loading the classes in the jar file
         * @throws Throwable
         *             if an error occurs
         */
        public static Loader run(ClassPool pool, MultiTransformClassFileTransformer tf, File jarFile, String[] args)
                        throws Throwable
        {
                final String mainClass = getMainClass(jarFile);

                if (mainClass == null)
                        throw new Exception("Failed to load Main-Class manifest attribute from " + jarFile);

                pool.appendClassPath(jarFile.getAbsolutePath());

                final ClassLoader parent = new URLClassLoader(new URL[] { jarFile.toURI().toURL() });

                return run(parent, pool, tf, mainClass, args);
        }

        /**
         * Get the main class from the manifest of the given jar file
         * 
         * @param jarFile
         *            the jar file
         * @return the main class or null if not found
         * @throws IOException
         *             if an error occurs when reading
         */
        public static String getMainClass(File jarFile) throws IOException {
                JarFile jar = null;

                try {
                        jar = new JarFile(jarFile);
                        final Manifest manifest = jar.getManifest();
                        final Attributes attr = manifest.getMainAttributes();
                        final String mainClass = attr.getValue("Main-Class");

                        return mainClass;
                } finally {
                        try {
                                if (jar != null)
                                        jar.close();
                        } catch (final IOException e) {
                        }
                }
        }

        /**
         * Run the main method of the given class, transforming any classes found on
         * the given classpath as they are loaded.
         * 
         * @param pool
         *            the classpool to hold classes as they are loaded
         * @param tf
         *            the transform(s) to apply
         * @param classpath
         *            the classpath on which to search for classes
         * @param mainClass
         *            the main class with the <code>main(String[])</code> method
         * @param args
         *            the arguments to pass to the main method
         * @return the classloader used for loading the classes in the jar file
         * @throws Throwable
         *             if an error occurs
         */
        public static Loader run(ClassPool pool, MultiTransformClassFileTransformer tf, String classpath, String mainClass,
                        String[] args)
                        throws Throwable
        {
                final String[] paths = classpath.split(File.pathSeparator);
                final URL[] urls = new URL[paths.length];
                for (int i = 0; i < paths.length; i++)
                        urls[i] = new File(paths[i]).toURI().toURL();

                final ClassLoader parent = new URLClassLoader(urls);

                pool.appendPathList(classpath);

                return run(parent, pool, tf, mainClass, args);
        }

        /**
         * Re-load the given class in a newly created {@link Loader} that is
         * configured to apply the given transform(s), and then run the main method.
         * 
         * @param transformer
         *            the transformer
         * @param clz
         *            the class
         * @param args
         *            the arguments
         * @throws Throwable
         *             if an error occurs
         */
        public static void run(MultiTransformClassFileTransformer transformer, Class<?> clz, String[] args) throws Throwable {
                final ClassPool pool = new ClassPool();
                pool.appendSystemPath();

                final Loader loader = new Loader(pool);

                // skip args4j
                loader.delegateLoadingOf("org.apache.log4j.");

                loader.addTranslator(pool, transformer);

                loader.run(clz.getName(), args);
        }

        protected static Loader run(final ClassLoader parent, ClassPool pool, MultiTransformClassFileTransformer tf,
                        String mainClass, String[] args)
                        throws Throwable
        {
                final Loader cl = new Loader(parent, pool);

                // Set the correct app name on OSX. Are there similar controls for other
                // platforms?
                System.setProperty("com.apple.mrj.application.apple.menu.about.name", mainClass);

                // skip args4j
                cl.delegateLoadingOf("org.apache.log4j.");

                cl.addTranslator(pool, tf);

                cl.run(mainClass, args);

                return cl;
        }

        /**
         * If the the given class has not already been loaded in by {@link Loader},
         * load it in a newly created {@link Loader} that is configured to apply the
         * given transform(s), run the main method and return true. If the class's
         * classload is a {@link Loader} then return false.
         * 
         * @param clz
         *            the class to load, transform and run
         * @param args
         *            the arguments to the main method
         * @param transformer
         *            the first transformer
         * @param transformers
         *            any additional transformers
         * @return true if the class has been reloaded; false otherwise
         * @throws Throwable
         *             if an error occurs.
         */
        public static boolean
                        run(Class<?> clz, String[] args, ClassTransformer transformer, ClassTransformer... transformers)
                                        throws Throwable
        {
                if (!(clz.getClassLoader() instanceof Loader)) {
                        final MultiTransformClassFileTransformer mtf =
                                        new MultiTransformClassFileTransformer(transformer, transformers);

                        ClassLoaderTransform.run(mtf, clz, args);

                        return true;
                }

                return false;
        }

        /**
         * Main method for an alternative in-place loading strategy. Allows a
         * self-contained program jar to automatically run {@link ClassTransformer}s
         * on itself.
         * <p>
         * Modify the assembled jar file so that the Main-Class is set as this class
         * (<code>org.openimaj.aop.classloader.ClassLoaderTransform</code>) and add
         * additional keys to the manifest to point at the actual class main (
         * {@link #MAIN_CLASS}) and the transformer classes ({@link #TRANSFORMERS},
         * separated by {@link #TRANSFORMERS_SEPARATOR}).
         * <p>
         * The specified transformer classes must all be instances of
         * {@link ClassTransformer} and also have a no-args constructor.
         * 
         * @param args
         *            the arguments to pass to the program being run
         * @throws Throwable
         *             if an error occurs
         */
        public static void main(String[] args) throws Throwable {
                final Class<ClassLoaderTransform> clazz = ClassLoaderTransform.class;
                final String className = clazz.getSimpleName() + ".class";
                final String classPath = clazz.getResource(className).toString();
                if (!classPath.startsWith("jar")) {
                        // Class not from JAR
                        return;
                }
                final String manifestPath = classPath.substring(0,
                                classPath.lastIndexOf("!") + 1) + "/META-INF/MANIFEST.MF";
                final Manifest manifest = new Manifest(new URL(manifestPath).openStream());
                final Attributes attr = manifest.getMainAttributes();

                final String mainClass = attr.getValue(MAIN_CLASS);
                final String[] tfs = attr.getValue(TRANSFORMERS).split(TRANSFORMERS_SEPARATOR);
                final ClassTransformer[] cts = new ClassTransformer[tfs.length];
                for (int i = 0; i < tfs.length; i++)
                        cts[i] = (ClassTransformer) Class.forName(tfs[i]).newInstance();

                final ClassPool cp = ClassPool.getDefault();

                run(null,
                                cp,
                                new MultiTransformClassFileTransformer(cts[0], Arrays.copyOfRange(cts, 1, cts.length)),
                                mainClass,
                                args);
        }
}