/*

 * Copyright (c) 2016, 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;

import java.util.Iterator;

import java.util.concurrent.Flow;

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

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

/**

 * A Publisher that publishes items obtained from the given Iterable. Each new

 * subscription gets a new Iterator.

 */

class PullPublisher<T> implements Flow.Publisher<T> {

    // Only one of `iterable` and `throwable` can be non-null. throwable is

    // non-null when an error has been encountered, by the creator of

    // PullPublisher, while subscribing the subscriber, but before subscribe has

    // completed.

    private final Iterable<T> iterable;

    private final Throwable throwable;

    PullPublisher(Iterable<T> iterable, Throwable throwable) {

        this.iterable = iterable;

        this.throwable = throwable;

    }

    PullPublisher(Iterable<T> iterable) {

        this(iterable, null);

    }

    @Override

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

        Subscription sub;

        if (throwable != null) {

            assert iterable == null : "non-null iterable: " + iterable;

            sub = new Subscription(subscriber, null, throwable);

        } else {

            assert throwable == null : "non-null exception: " + throwable;

            sub = new Subscription(subscriber, iterable.iterator(), null);

        }

        subscriber.onSubscribe(sub);

        if (throwable != null) {

            sub.pullScheduler.runOrSchedule();

        }

    }

    private class Subscription implements Flow.Subscription {

        private final Flow.Subscriber<? super T> subscriber;

        private final Iterator<T> iter;

        private volatile boolean completed;

        private volatile boolean cancelled;

        private volatile Throwable error;

        final SequentialScheduler pullScheduler = new SequentialScheduler(new PullTask());

        private final Demand demand = new Demand();

        Subscription(Flow.Subscriber<? super T> subscriber,

                     Iterator<T> iter,

                     Throwable throwable) {

            this.subscriber = subscriber;

            this.iter = iter;

            this.error = throwable;

        }

        final class PullTask extends SequentialScheduler.CompleteRestartableTask {

            @Override

            protected void run() {

                if (completed || cancelled) {

                    return;

                }

                Throwable t = error;

                if (t != null) {

                    completed = true;

                    pullScheduler.stop();

                    subscriber.onError(t);

                    return;

                }

                while (demand.tryDecrement() && !cancelled) {

                    if (!iter.hasNext()) {

                        break;

                    } else {

                        subscriber.onNext(iter.next());

                    }

                }

                if (!iter.hasNext() && !cancelled) {

                    completed = true;

                    pullScheduler.stop();

                    subscriber.onComplete();

                }

            }

        }

        @Override

        public void request(long n) {

            if (cancelled)

                return;  // no-op

            if (n <= 0) {

                error = new IllegalArgumentException("illegal non-positive request:" + n);

            } else {

                demand.increase(n);

            }

            pullScheduler.runOrSchedule();

        }

        @Override

        public void cancel() {

            cancelled = true;

        }

    }

}