/*

 * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

import java.io.*;

import java.lang.reflect.*;

import java.util.jar.*;

public class Util {

    /**

     * Invoke the loader.defineClass() class method to define the class stored in clsFile,

     * with the following modification:

     * <ul>

     *  <li> All ASCII strings in the class file bytes that matches fromString will be replaced with toString.

     *       NOTE: the two strings must be the exact same length.

     * </ul>

     */

    public static Class defineModifiedClass(ClassLoader loader, File clsFile, String fromString, String toString)

        throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,

               InvocationTargetException

    {

      try (DataInputStream dis = new DataInputStream(new FileInputStream(clsFile))) {

        byte[] buff = new byte[(int)clsFile.length()];

        dis.readFully(buff);

        replace(buff, fromString, toString);

        System.out.println("Loading from: " + clsFile + " (" + buff.length + " bytes)");

        Method defineClass = ClassLoader.class.getDeclaredMethod("defineClass",

                                                                 buff.getClass(), int.class, int.class);

        defineClass.setAccessible(true);

        // We directly call into ClassLoader.defineClass() to define the "Super" class. Also,

        // rewrite its classfile so that it returns ___yyy___ instead of ___xxx___. Changing the

        // classfile will guarantee that this class will NOT be loaded from the CDS archive.

        Class cls = (Class)defineClass.invoke(loader, buff, new Integer(0), new Integer(buff.length));

        System.out.println("Loaded : " + cls);

        return cls;

      }

    }

    /**

     * @return the number of occurrences of the <code>from</code> string that

     * have been replaced.

     */

    public static int replace(byte buff[], String from, String to) {

        if (to.length() != from.length()) {

            throw new RuntimeException("bad strings");

        }

        byte f[] = asciibytes(from);

        byte t[] = asciibytes(to);

        byte f0 = f[0];

        int numReplaced = 0;

        int max = buff.length - f.length;

        for (int i=0; i<max; ) {

            if (buff[i] == f0 && replace(buff, f, t, i)) {

                i += f.length;

                numReplaced ++;

            } else {

                i++;

            }

        }

        return numReplaced;

    }

    public static boolean replace(byte buff[], byte f[], byte t[], int i) {

        for (int x=0; x<f.length; x++) {

            if (buff[x+i] != f[x]) {

                return false;

            }

        }

        for (int x=0; x<f.length; x++) {

            buff[x+i] = t[x];

        }

        return true;

    }

    static byte[] asciibytes(String s) {

        byte b[] = new byte[s.length()];

        for (int i=0; i<b.length; i++) {

            b[i] = (byte)s.charAt(i);

        }

        return b;

    }

    public static Class defineClassFromJAR(ClassLoader loader, File jarFile, String className)

        throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,

               InvocationTargetException {

        return defineClassFromJAR(loader, jarFile, className, null, null);

    }

    /**

     * Invoke the loader.defineClass() class method to define the named class stored in a JAR file.

     *

     * If a class exists both in the classpath, as well as in the list of URLs of a URLClassLoader,

     * by default, the URLClassLoader will not define the class, and instead will delegate to the

     * app loader. This method is an easy way to force the class to be defined by the URLClassLoader.

     *

     * Optionally, you can modify the contents of the classfile buffer. See comments in

     * defineModifiedClass.

     */

    public static Class defineClassFromJAR(ClassLoader loader, File jarFile, String className,

                                           String fromString, String toString)

        throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,

               InvocationTargetException

    {

        byte[] buff = getClassFileFromJar(jarFile, className);

        if (fromString != null) {

            replace(buff, fromString, toString);

        }

        //System.out.println("Loading from: " + ent + " (" + buff.length + " bytes)");

        Method defineClass = ClassLoader.class.getDeclaredMethod("defineClass",

                                                                 buff.getClass(), int.class, int.class);

        defineClass.setAccessible(true);

        Class cls = (Class)defineClass.invoke(loader, buff, new Integer(0), new Integer(buff.length));

        //System.out.println("Loaded : " + cls);

        return cls;

    }

    public static byte[] getClassFileFromJar(File jarFile, String className) throws FileNotFoundException, IOException {

        JarFile jf = new JarFile(jarFile);

        JarEntry ent = jf.getJarEntry(className.replace('.', '/') + ".class");

        try (DataInputStream dis = new DataInputStream(jf.getInputStream(ent))) {

            byte[] buff = new byte[(int)ent.getSize()];

            dis.readFully(buff);

            return buff;

        }

    }

}