/*

 * 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.  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.incubator.http.internal.websocket;

import java.io.IOException;

import java.nio.channels.SelectionKey;

import java.util.concurrent.atomic.AtomicBoolean;

import java.util.function.Consumer;

import static java.util.Objects.requireNonNull;

/*

 * Sends messages one at a time, in an asynchronous and non-blocking fashion.

 *

 * No matter whether the message has been fully sent or an error has occurred,

 * the transmitter reports the outcome to the supplied handler and becomes ready

 * to accept a new message. Until then, the transmitter is considered "busy" and

 * an IllegalStateException will be thrown on each attempt to invoke send.

 */

public class Transmitter {

    /* This flag is used solely for assertions */

    private final AtomicBoolean busy = new AtomicBoolean();

    private OutgoingMessage message;

    private Consumer<Exception> completionHandler;

    private final RawChannel channel;

    private final RawChannel.RawEvent event;

    public Transmitter(RawChannel channel) {

        this.channel = channel;

        this.event = createHandler();

    }

    /**

     * The supplied handler may be invoked in the calling thread.

     * A {@code StackOverflowError} may thus occur if there's a possibility

     * that this method is called again by the supplied handler.

     */

    public void send(OutgoingMessage message,

                     Consumer<Exception> completionHandler)

    {

        requireNonNull(message);

        requireNonNull(completionHandler);

        if (!busy.compareAndSet(false, true)) {

            throw new IllegalStateException();

        }

        send0(message, completionHandler);

    }

    public void close() throws IOException {

        channel.shutdownOutput();

    }

    private RawChannel.RawEvent createHandler() {

        return new RawChannel.RawEvent() {

            @Override

            public int interestOps() {

                return SelectionKey.OP_WRITE;

            }

            @Override

            public void handle() {

                // registerEvent(e) happens-before subsequent e.handle(), so

                // we're fine reading the stored message and the completionHandler

                send0(message, completionHandler);

            }

        };

    }

    private void send0(OutgoingMessage message, Consumer<Exception> handler) {

        boolean b = busy.get();

        assert b; // Please don't inline this, as busy.get() has memory

                  // visibility effects and we don't want the program behaviour

                  // to depend on whether the assertions are turned on

                  // or turned off

        try {

            boolean sent = message.sendTo(channel);

            if (sent) {

                busy.set(false);

                handler.accept(null);

            } else {

                // The message has not been fully sent, the transmitter needs to

                // remember the message until it can continue with sending it

                this.message = message;

                this.completionHandler = handler;

                try {

                    channel.registerEvent(event);

                } catch (IOException e) {

                    this.message = null;

                    this.completionHandler = null;

                    busy.set(false);

                    handler.accept(e);

                }

            }

        } catch (IOException e) {

            busy.set(false);

            handler.accept(e);

        }

    }

}