/*

 * 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.incubator.http;

import java.util.Optional;

import java.util.concurrent.Flow;

import jdk.incubator.http.internal.common.Log;

/**

 * A Publisher which is assumed to run in its own thread.

 *

 * acceptData() may therefore block while waiting for subscriber demand

 */

class BlockingPushPublisher<T> extends AbstractPushPublisher<T> {

    volatile Subscription subscription;

    volatile Flow.Subscriber<? super T> subscriber;

    volatile SubscriptionState state;

    long demand;

    @Override

    public void subscribe(Flow.Subscriber<? super T> subscriber) {

        state = SubscriptionState.OPENED;

        subscription = new Subscription(subscriber);

        subscriber.onSubscribe(subscription);

    }

    /**

     * Entry point for supplying items to publisher. This call will block

     * when no demand available.

     */

    @Override

    public void acceptData(Optional<T> item) throws InterruptedException {

        SubscriptionState s = this.state;

        // do not use switch(this.state): this.state could be null.

        if (s == SubscriptionState.CANCELLED) return;

        if (s == SubscriptionState.DONE) {

            throw new IllegalStateException("subscription complete");

        }

        if (!item.isPresent()) {

            subscriber.onComplete();

            this.state = SubscriptionState.DONE;

        } else {

            obtainPermit();

            if (this.state == SubscriptionState.CANCELLED) return;

            subscriber.onNext(item.get());

        }

    }

    /**

     * Terminates the publisher with given exception.

     */

    @Override

    public void acceptError(Throwable t) {

        if (this.state != SubscriptionState.OPENED) {

            Log.logError(t);

            return;

        }

        subscriber.onError(t);

        cancel();

    }

    private synchronized void obtainPermit() throws InterruptedException {

        while (demand == 0) {

            wait();

        }

        if (this.state == SubscriptionState.DONE) {

            throw new IllegalStateException("subscription complete");

        }

        demand --;

    }

    synchronized void addPermits(long n) {

        long old = demand;

        demand += n;

        if (old == 0) {

            notifyAll();

        }

    }

    synchronized void cancel() {

        this.state = SubscriptionState.CANCELLED;

        notifyAll();

    }

    private class Subscription implements Flow.Subscription {

        Subscription(Flow.Subscriber<? super T> subscriber) {

            BlockingPushPublisher.this.subscriber = subscriber;

        }

        @Override

        public void request(long n) {

            addPermits(n);

        }

        @Override

        public void cancel() {

            BlockingPushPublisher.this.cancel();

        }

    }

}