/*

 * 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  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  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  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 java.net.http;

import java.io.IOException;

import java.nio.ByteBuffer;

import java.nio.channels.SelectionKey;

import java.util.function.Consumer;

import static java.util.Objects.requireNonNull;

/*

 * Writes ByteBuffer[] to the channel in a non-blocking, asynchronous fashion.

 *

 * A client attempts to write data by calling

 *

 *     boolean tryWriteFully(ByteBuffer[] buffers)

 *

 * If the attempt was successful and all the data has been written, then the

 * method returns `true`.

 *

 * If the data has been written partially, then the method returns `false`, and

 * the writer (this object) attempts to complete the write asynchronously by

 * calling, possibly more than once

 *

 *     boolean tryCompleteWrite()

 *

 * in its own threads.

 *

 * When the write has been completed asynchronously, the callback is signalled

 * with `null`.

 *

 * If an error occurs in any of these stages it will NOT be thrown from the

 * method. Instead `false` will be returned and the exception will be signalled

 * to the callback. This is done in order to handle all exceptions in a single

 * place.

 */

final class WSWriter {

    private final RawChannel channel;

    private final RawChannel.NonBlockingEvent writeReadinessHandler;

    private final Consumer<Throwable> completionCallback;

    private ByteBuffer[] buffers;

    private int offset;

    WSWriter(RawChannel channel, Consumer<Throwable> completionCallback) {

        this.channel = channel;

        this.completionCallback = completionCallback;

        this.writeReadinessHandler = createHandler();

    }

    boolean tryWriteFully(ByteBuffer[] buffers) {

        synchronized (this) {

            this.buffers = requireNonNull(buffers);

            this.offset = 0;

        }

        return tryCompleteWrite();

    }

    private final boolean tryCompleteWrite() {

        try {

            return writeNow();

        } catch (IOException e) {

            completionCallback.accept(e);

            return false;

        }

    }

    private boolean writeNow() throws IOException {

        synchronized (this) {

            for (; offset != -1; offset = nextUnwrittenIndex(buffers, offset)) {

                long bytesWritten = channel.write(buffers, offset, buffers.length - offset);

                if (bytesWritten == 0) {

                    channel.registerEvent(writeReadinessHandler);

                    return false;

                }

            }

            return true;

        }

    }

    private static int nextUnwrittenIndex(ByteBuffer[] buffers, int offset) {

        for (int i = offset; i < buffers.length; i++) {

            if (buffers[i].hasRemaining()) {

                return i;

            }

        }

        return -1;

    }

    private RawChannel.NonBlockingEvent createHandler() {

        return new RawChannel.NonBlockingEvent() {

            @Override

            public int interestOps() {

                return SelectionKey.OP_WRITE;

            }

            @Override

            public void handle() {

                if (tryCompleteWrite()) {

                    completionCallback.accept(null);

                }

            }

            @Override

            public String toString() {

                return "Write readiness event [" + channel + "]";

            }

        };

    }

}