/*

 * Copyright (c) 2018, 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.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * 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.

 */

package jdk.jfr.event.oldobject;

import java.io.IOException;

import java.io.InputStream;

import java.util.ArrayList;

import java.util.List;

/*

 * A special class loader that will, for our test class, make sure that each

 * load will become a unique class

 */

public final class TestClassLoader extends ClassLoader {

    public static final class TestClass0000000 {

        public static final byte[] oneByte = new byte[1];

    }

    static byte[] classByteCode = readTestClassBytes();

    private static int classIdCounter;

    TestClassLoader() {

        super(TestClassLoader.class.getClassLoader());

    }

    public List<Class<?>> loadClasses(int count) throws Exception {

        List<Class<?>> classes = new ArrayList<>();

        for (int i = 0; i < count; i++) {

            String className = "jdk.jfr.event.oldobject.TestClassLoader$";

            className += "TestClass" + String.format("%07d", classIdCounter++);

            Class<?> clazz = Class.forName(className, true, this);

            classes.add(clazz);

        }

        return classes;

    }

    @Override

    protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {

        // If not loading the test class, just go on with the normal class loader

        if (!name.contains("TestClass")) {

            return super.loadClass(name, resolve);

        }

        String[] classNameParts = name.split("\\$");

        String newName = classNameParts[1];

        String oldName = "TestClass0000000";

        if (oldName.length() != newName.length()) {

            throw new AssertionError("String lengths don't match. Unable to replace class name");

        }

        byte[] newBytes = classByteCode.clone();

        replaceBytes(newBytes, oldName.getBytes(), newName.getBytes());

        Class<?> c = defineClass(name, newBytes, 0, newBytes.length);

        if (resolve) {

            resolveClass(c);

        }

        return c;

    }

    static void replaceBytes(byte[] bytes, byte[] find, byte[] replacement) {

        for (int index = 0; index < bytes.length - find.length; index++) {

            if (matches(bytes, index, find)) {

                replace(bytes, index, replacement);

            }

        }

    }

    private static void replace(byte[] bytes, int startIndex, byte[] replacement) {

        for (int index = 0; index < replacement.length; index++) {

            bytes[startIndex + index] = replacement[index];

        }

    }

    private static boolean matches(byte[] bytes, int startIndex, byte[] matching) {

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

            if (bytes[startIndex + i] != matching[i]) {

                return false;

            }

        }

        return true;

    }

    private static byte[] readTestClassBytes() {

        try {

            String classFileName = "jdk/jfr/event/oldobject/TestClassLoader$TestClass0000000.class";

            InputStream is = TestClassLoader.class.getClassLoader().getResourceAsStream(classFileName);

            if (is == null) {

                throw new RuntimeException("Culd not find class file " + classFileName);

            }

            byte[] b = is.readAllBytes();

            is.close();

            return b;

        } catch (IOException ioe) {

            ioe.printStackTrace();

            throw new RuntimeException(ioe);

        }

    }

}