/*

 * Copyright (c) 2013, 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.

 *

 * 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.DataInputStream;

import java.io.ByteArrayOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileWriter;

import java.io.IOException;

import java.io.PrintWriter;

import javax.tools.JavaCompiler;

import javax.tools.ToolProvider;

/**

 * A class loader that generates new classes.

 * The generated classes are made by first emitting java sources with nested

 * static classes, these are then compiled and the class files are read back.

 * Some efforts are made to make the class instances unique and of not insignificant

 * size.

 */

public class GeneratedClassLoader extends ClassLoader {

    /**

     * Holds a pair of class bytecodes and class name (for use with defineClass).

     */

    private static class GeneratedClass {

        public byte[] bytes;

        public String name;

        public GeneratedClass(byte[] bytes, String name) {

            this.bytes = bytes; this.name = name;

        }

    }

    /**

     * Used to uniquely name every class generated.

     */

    private static int count = 0;

    /**

     * Used to enable/disable keeping the class files and java sources for

     * the generated classes.

     */

    private static boolean deleteFiles = Boolean.parseBoolean(

        System.getProperty("GeneratedClassLoader.deleteFiles", "true"));

    private static String bigstr =

        "Lorem ipsum dolor sit amet, consectetur adipiscing elit. "

        + "In facilisis scelerisque vehicula. Donec congue nisi a "

        + "leo posuere placerat lobortis felis ultrices. Pellentesque "

        + "habitant morbi tristique senectus et netus et malesuada "

        + "fames ac turpis egestas. Nam tristique velit at felis "

        + "iaculis at tempor sem vestibulum. Sed adipiscing lectus "

        + "non mi molestie sagittis. Morbi eu purus urna. Nam tempor "

        + "tristique massa eget semper. Mauris cursus, nulla et ornare "

        + "vehicula, leo dolor scelerisque metus, sit amet rutrum erat "

        + "sapien quis dui. Nullam eleifend risus et velit accumsan sed "

        + "suscipit felis pulvinar. Nullam faucibus suscipit gravida. "

        + "Pellentesque habitant morbi tristique senectus et netus et "

        + "malesuada fames ac turpis egestas. Nullam ut massa augue, "

        + "nec viverra mauris.";

    private static int getNextCount() {

        return count++;

    }

    ////// end statics

    private JavaCompiler javac;

    private String nameBase;

    public GeneratedClassLoader() {

        javac = ToolProvider.getSystemJavaCompiler();

        nameBase = "TestSimpleClass";

    }

    private long getBigValue(int which) {

        // > 65536 is too large to encode in the bytecode

        // so this will force us to emit a constant pool entry for this int

        return (long)which + 65537;

    }

    private String getBigString(int which) {

        return bigstr + which;

    }

    private String getClassName(int count) {

        return nameBase + count;

    }

    private String generateSource(int count, int sizeFactor, int numClasses) {

        StringBuilder sb = new StringBuilder();

        sb.append("public class ").append(getClassName(count)).append("{\n");

        for (int j = 0; j < numClasses; ++j) {

            sb.append("public static class ")

              .append("Class")

              .append(j)

              .append("{\n");

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

                int value = i;

                sb.append("private long field")

                  .append(i).append(" = ")

                  .append(getBigValue(value++))

                  .append(";\n");

                sb.append("public long method")

                  .append(i)

                  .append("() {\n");

                sb.append("return ")

                  .append(getBigValue(value++))

                  .append(";");

                sb.append("}\n");

                sb.append("private String str").append(i)

                  .append(" = \"")

                  .append(getBigString(i))

                  .append("\";");

            }

            sb.append("\n}");

        }

        sb.append("\n}");

        return sb.toString();

    }

    private GeneratedClass[] getGeneratedClass(int sizeFactor, int numClasses) throws IOException {

        int uniqueCount = getNextCount();

        String src = generateSource(uniqueCount, sizeFactor, numClasses);

        String className = getClassName(uniqueCount);

        File file = new File(className + ".java");

        try (PrintWriter pw = new PrintWriter(new FileWriter(file))) {

            pw.append(src);

            pw.flush();

        }

        ByteArrayOutputStream err = new ByteArrayOutputStream();

        int exitcode = javac.run(null, null, err, file.getCanonicalPath());

        if (exitcode != 0) {

            // Print Error

            System.err.print(err);

            if (err.toString().contains("java.lang.OutOfMemoryError: Java heap space")) {

              throw new OutOfMemoryError("javac failed with resources exhausted");

            } else {

              throw new RuntimeException("javac failure when compiling: " +

                      file.getCanonicalPath());

            }

        } else {

            if (deleteFiles) {

                file.delete();

            }

        }

        GeneratedClass[] gc = new GeneratedClass[numClasses];

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

            String name = className + "$" + "Class" + i;

            File classFile = new File(name + ".class");

            byte[] bytes;

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

                bytes = new byte[dis.available()];

                dis.readFully(bytes);

            }

            if (deleteFiles) {

                classFile.delete();

            }

            gc[i] = new GeneratedClass(bytes, name);

        }

        if (deleteFiles) {

            new File(className + ".class").delete();

        }

        return gc;

    }

    /**

     * Generate a single class, compile it and load it.

     * @param sizeFactor Fuzzy measure of how large the class should be.

     * @return the Class instance.

     * @throws IOException

     */

    public Class<?> generateClass(int sizeFactor) throws IOException {

        return getGeneratedClasses(sizeFactor, 1)[0];

    }

    /**

     * Generate several classes, compile and load them.

     * @param sizeFactor Fuzzy measure of how large each class should be.

     * @param numClasses The number of classes to create

     * @return an array of the Class instances.

     * @throws IOException

     */

    public Class<?>[] getGeneratedClasses(int sizeFactor, int numClasses) throws IOException {

        GeneratedClass[] gc = getGeneratedClass(sizeFactor, numClasses);

        Class<?>[] classes = new Class[numClasses];

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

            classes[i] = defineClass(gc[i].name, gc[i].bytes, 0 , gc[i].bytes.length);

        }

        return classes;

    }

}