/*

 * Copyright (c) 2017, 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.  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.

 */

import java.util.concurrent.Flow;

import java.util.concurrent.atomic.AtomicBoolean;

/**

 * Maintains subscription counter and provides primitives for

 * - accessing window

 * - reducing window when delivering items externally

 * - resume delivery when window was zero previously

 *

 * @author mimcmah

 */

public class SubscriptionBase implements Flow.Subscription {

    final Demand demand = new Demand();

    final SequentialScheduler scheduler; // when window was zero and is opened, run this

    final Runnable cancelAction; // when subscription cancelled, run this

    final AtomicBoolean cancelled;

    public SubscriptionBase(SequentialScheduler scheduler, Runnable cancelAction) {

        this.scheduler = scheduler;

        this.cancelAction = cancelAction;

        this.cancelled = new AtomicBoolean(false);

    }

    @Override

    public void request(long n) {

        if (demand.increase(n))

            scheduler.runOrSchedule();

    }

    @Override

    public synchronized String toString() {

        return "SubscriptionBase: window = " + demand.get() +

                " cancelled = " + cancelled.toString();

    }

    /**

     * Returns true if the window was reduced by 1. In that case

     * items must be supplied to subscribers and the scheduler run

     * externally. If the window could not be reduced by 1, then false

     * is returned and the scheduler will run later when the window is updated.

     */

    public boolean tryDecrement() {

        return demand.tryDecrement();

    }

    public long window() {

        return demand.get();

    }

    @Override

    public void cancel() {

        if (cancelled.getAndSet(true))

            return;

        scheduler.stop();

        cancelAction.run();

    }

}