/*

 * Copyright (c) 2016, 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.jshell.execution;

import jdk.jshell.spi.ExecutionEnv;

import java.io.IOException;

import java.io.InputStream;

import java.io.ObjectInput;

import java.io.ObjectInputStream;

import java.io.ObjectOutput;

import java.io.ObjectOutputStream;

import java.io.OutputStream;

import java.util.Map;

import java.util.Map.Entry;

import java.util.function.Consumer;

import com.sun.jdi.VirtualMachine;

import jdk.jshell.spi.ExecutionControl;

/**

 * Miscellaneous utility methods for setting-up implementations of

 * {@link ExecutionControl}. Particularly implementations with remote

 * execution.

 *

 * @author Jan Lahoda

 * @author Robert Field

 */

public class Util {

    // never instanciated

    private Util() {}

    /**

     * Create a composite {@link ExecutionControl.Generator} instance that, when

     * generating, will try each specified generator until successfully creating

     * an {@link ExecutionControl} instance, or, if all fail, will re-throw the

     * first exception.

     *

     * @param gec0 the first instance to try

     * @param gecs the second through Nth instance to try

     * @return the fail-over generator

     */

    public static ExecutionControl.Generator failOverExecutionControlGenerator(

            ExecutionControl.Generator gec0, ExecutionControl.Generator... gecs) {

        return (ExecutionEnv env) -> {

            Throwable thrown;

            try {

                return gec0.generate(env);

            } catch (Throwable ex) {

                thrown = ex;

            }

            for (ExecutionControl.Generator gec : gecs) {

                try {

                    return gec.generate(env);

                } catch (Throwable ignore) {

                    // only care about the first, and only if they all fail

                }

            }

            throw thrown;

        };

    }

    /**

     * Forward commands from the input to the specified {@link ExecutionControl}

     * instance, then responses back on the output.

     * @param ec the direct instance of {@link ExecutionControl} to process commands

     * @param in the command input

     * @param out the command response output

     */

    public static void forwardExecutionControl(ExecutionControl ec,

            ObjectInput in, ObjectOutput out) {

        new ExecutionControlForwarder(ec, in, out).commandLoop();

    }

    /**

     * Forward commands from the input to the specified {@link ExecutionControl}

     * instance, then responses back on the output.

     * @param ec the direct instance of {@link ExecutionControl} to process commands

     * @param inStream the stream from which to create the command input

     * @param outStream the stream that will carry {@code System.out},

     * {@code System.err}, any specified auxiliary channels, and the

     * command response output.

     * @param streamMap a map between names of additional streams to carry and setters

     * for the stream

     * @throws IOException if there are errors using the passed streams

     */

    public static void forwardExecutionControlAndIO(ExecutionControl ec,

            InputStream inStream, OutputStream outStream,

            Map<String, Consumer<OutputStream>> streamMap) throws IOException {

        ObjectInputStream cmdIn = new ObjectInputStream(inStream);

        for (Entry<String, Consumer<OutputStream>> e : streamMap.entrySet()) {

            e.getValue().accept(multiplexingOutputStream(e.getKey(), outStream));

        }

        ObjectOutputStream cmdOut = new ObjectOutputStream(multiplexingOutputStream("command", outStream));

        forwardExecutionControl(ec, cmdIn, cmdOut);

    }

    static OutputStream multiplexingOutputStream(String label, OutputStream outputStream) {

        return new MultiplexingOutputStream(label, outputStream);

    }

    /**

     * Reads from an InputStream which has been packetized and write its contents

     * to the out and err OutputStreams; Copies the command stream.

     * @param input the packetized input stream

     * @param streamMap a map between stream names and the output streams to forward

     * @return the command stream

     * @throws IOException if setting up the streams raised an exception

     */

    public static ObjectInput remoteInput(InputStream input,

            Map<String, OutputStream> streamMap) throws IOException {

        PipeInputStream commandIn = new PipeInputStream();

        new DemultiplexInput(input, commandIn, streamMap).start();

        return new ObjectInputStream(commandIn);

    }

    /**

     * Monitor the JDI event stream for {@link com.sun.jdi.event.VMDeathEvent}

     * and {@link com.sun.jdi.event.VMDisconnectEvent}. If encountered, invokes

     * {@code unbiddenExitHandler}.

     *

     * @param vm the virtual machine to check

     * @param unbiddenExitHandler the handler, which will accept the exit

     * information

     */

    public static void detectJDIExitEvent(VirtualMachine vm, Consumer<String> unbiddenExitHandler) {

        if (vm.canBeModified()) {

            new JDIEventHandler(vm, unbiddenExitHandler).start();

        }

    }

    /**

     * Creates a Thread that will ship all input to the remote agent.

     *

     * @param inputStream the user input

     * @param outStream the input to the remote agent

     * @param handler a failure handler

     */

    public static void forwardInputToRemote(final InputStream inputStream,

            final OutputStream outStream, final Consumer<Exception> handler) {

        Thread thr = new Thread("input reader") {

            @Override

            public void run() {

                try {

                    byte[] buf = new byte[256];

                    int cnt;

                    while ((cnt = inputStream.read(buf)) != -1) {

                        outStream.write(buf, 0, cnt);

                        outStream.flush();

                    }

                } catch (Exception ex) {

                    handler.accept(ex);

                }

            }

        };

        thr.setPriority(Thread.MAX_PRIORITY - 1);

        thr.start();

    }

}