/*

 * Copyright (c) 2013, 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.

 */

package com.oracle.java.testlibrary;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.OutputStream;

import java.net.URI;

import java.util.Arrays;

import javax.tools.ForwardingJavaFileManager;

import javax.tools.ForwardingJavaFileManager;

import javax.tools.FileObject;

import javax.tools.JavaCompiler;

import javax.tools.JavaCompiler.CompilationTask;

import javax.tools.JavaFileManager;

import javax.tools.JavaFileObject;

import javax.tools.JavaFileObject.Kind;

import javax.tools.SimpleJavaFileObject;

import javax.tools.ToolProvider;

/**

 * {@code InMemoryJavaCompiler} can be used for compiling a {@link

 * CharSequence} to a {@code byte[]}.

 *

 * The compiler will not use the file system at all, instead using a {@link

 * ByteArrayOutputStream} for storing the byte code. For the source code, any

 * kind of {@link CharSequence} can be used, e.g. {@link String}, {@link

 * StringBuffer} or {@link StringBuilder}.

 *

 * The {@code InMemoryCompiler} can easily be used together with a {@code

 * ByteClassLoader} to easily compile and load source code in a {@link String}:

 *

 * <pre>

 * {@code

 * import com.oracle.java.testlibrary.InMemoryJavaCompiler;

 * import com.oracle.java.testlibrary.ByteClassLoader;

 *

 * class Example {

 *     public static void main(String[] args) {

 *         String className = "Foo";

 *         String sourceCode = "public class " + className + " {" +

 *                             "    public void bar() {" +

 *                             "        System.out.println("Hello from bar!");" +

 *                             "    }" +

 *                             "}";

 *         byte[] byteCode = InMemoryJavaCompiler.compile(className, sourceCode);

 *         Class fooClass = ByteClassLoader.load(className, byteCode);

 *     }

 * }

 * }

 * </pre>

 */

public class InMemoryJavaCompiler {

    private static class MemoryJavaFileObject extends SimpleJavaFileObject {

        private final String className;

        private final CharSequence sourceCode;

        private final ByteArrayOutputStream byteCode;

        public MemoryJavaFileObject(String className, CharSequence sourceCode) {

            super(URI.create("string:///" + className.replace('.','/') + Kind.SOURCE.extension), Kind.SOURCE);

            this.className = className;

            this.sourceCode = sourceCode;

            this.byteCode = new ByteArrayOutputStream();

        }

        @Override

        public CharSequence getCharContent(boolean ignoreEncodingErrors) {

            return sourceCode;

        }

        @Override

        public OutputStream openOutputStream() throws IOException {

            return byteCode;

        }

        public byte[] getByteCode() {

            return byteCode.toByteArray();

        }

        public String getClassName() {

            return className;

        }

    }

    private static class FileManagerWrapper extends ForwardingJavaFileManager {

        private MemoryJavaFileObject file;

        public FileManagerWrapper(MemoryJavaFileObject file) {

            super(getCompiler().getStandardFileManager(null, null, null));

            this.file = file;

        }

        @Override

        public JavaFileObject getJavaFileForOutput(Location location, String className,

                                                   Kind kind, FileObject sibling)

            throws IOException {

            if (!file.getClassName().equals(className)) {

                throw new IOException("Expected class with name " + file.getClassName() +

                                      ", but got " + className);

            }

            return file;

        }

    }

    /**

     * Compiles the class with the given name and source code.

     *

     * @param className The name of the class

     * @param sourceCode The source code for the class with name {@code className}

     * @throws RuntimeException if the compilation did not succeed

     * @return The resulting byte code from the compilation

     */

    public static byte[] compile(String className, CharSequence sourceCode) {

        MemoryJavaFileObject file = new MemoryJavaFileObject(className, sourceCode);

        CompilationTask task = getCompilationTask(file);

        if(!task.call()) {

            throw new RuntimeException("Could not compile " + className + " with source code " + sourceCode);

        }

        return file.getByteCode();

    }

    private static JavaCompiler getCompiler() {

        return ToolProvider.getSystemJavaCompiler();

    }

    private static CompilationTask getCompilationTask(MemoryJavaFileObject file) {

        return getCompiler().getTask(null, new FileManagerWrapper(file), null, null, null, Arrays.asList(file));

    }

}