Copyright (c) 2016-present, RxJava Contributors.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is
distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
the License for the specific language governing permissions and limitations under the License.
/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */

package io.reactivex.internal.operators.flowable;

import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.exceptions.MissingBackpressureException;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.BackpressureHelper;
import io.reactivex.subscribers.SerializedSubscriber;

public final class FlowableSamplePublisher<T> extends Flowable<T> {
    final Publisher<T> source;
    final Publisher<?> other;

    final boolean emitLast;

    public FlowableSamplePublisher(Publisher<T> source, Publisher<?> other, boolean emitLast) {
        this.source = source;
        this.other = other;
        this.emitLast = emitLast;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {
        SerializedSubscriber<T> serial = new SerializedSubscriber<T>(s);
        if (emitLast) {
            source.subscribe(new SampleMainEmitLast<T>(serial, other));
        } else {
            source.subscribe(new SampleMainNoLast<T>(serial, other));
        }
    }

    abstract static class SamplePublisherSubscriber<T> extends AtomicReference<T> implements FlowableSubscriber<T>, Subscription {

        private static final long serialVersionUID = -3517602651313910099L;

        final Subscriber<? super T> downstream;
        final Publisher<?> sampler;

        final AtomicLong requested = new AtomicLong();

        final AtomicReference<Subscription> other = new AtomicReference<Subscription>();

        Subscription upstream;

        SamplePublisherSubscriber(Subscriber<? super T> actual, Publisher<?> other) {
            this.downstream = actual;
            this.sampler = other;
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(this.upstream, s)) {
                this.upstream = s;
                downstream.onSubscribe(this);
                if (other.get() == null) {
                    sampler.subscribe(new SamplerSubscriber<T>(this));
                    s.request(Long.MAX_VALUE);
                }
            }

        }

        @Override
        public void onNext(T t) {
            lazySet(t);
        }

        @Override
        public void onError(Throwable t) {
            SubscriptionHelper.cancel(other);
            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            SubscriptionHelper.cancel(other);
            completion();
        }

        void setOther(Subscription o) {
            SubscriptionHelper.setOnce(other, o, Long.MAX_VALUE);
        }

        @Override
        public void request(long n) {
            if (SubscriptionHelper.validate(n)) {
                BackpressureHelper.add(requested, n);
            }
        }

        @Override
        public void cancel() {
            SubscriptionHelper.cancel(other);
            upstream.cancel();
        }

        public void error(Throwable e) {
            upstream.cancel();
            downstream.onError(e);
        }

        public void complete() {
            upstream.cancel();
            completion();
        }

        void emit() {
            T value = getAndSet(null);
            if (value != null) {
                long r = requested.get();
                if (r != 0L) {
                    downstream.onNext(value);
                    BackpressureHelper.produced(requested, 1);
                } else {
                    cancel();
                    downstream.onError(new MissingBackpressureException("Couldn't emit value due to lack of requests!"));
                }
            }
        }

        abstract void completion();

        abstract void run();
    }

    static final class SamplerSubscriber<T> implements FlowableSubscriber<Object> {
        final SamplePublisherSubscriber<T> parent;
        SamplerSubscriber(SamplePublisherSubscriber<T> parent) {
            this.parent = parent;

        }

        @Override
        public void onSubscribe(Subscription s) {
            parent.setOther(s);
        }

        @Override
        public void onNext(Object t) {
            parent.run();
        }

        @Override
        public void onError(Throwable t) {
            parent.error(t);
        }

        @Override
        public void onComplete() {
            parent.complete();
        }
    }

    static final class SampleMainNoLast<T> extends SamplePublisherSubscriber<T> {

        private static final long serialVersionUID = -3029755663834015785L;

        SampleMainNoLast(Subscriber<? super T> actual, Publisher<?> other) {
            super(actual, other);
        }

        @Override
        void completion() {
            downstream.onComplete();
        }

        @Override
        void run() {
            emit();
        }
    }

    static final class SampleMainEmitLast<T> extends SamplePublisherSubscriber<T> {

        private static final long serialVersionUID = -3029755663834015785L;

        final AtomicInteger wip;

        volatile boolean done;

        SampleMainEmitLast(Subscriber<? super T> actual, Publisher<?> other) {
            super(actual, other);
            this.wip = new AtomicInteger();
        }

        @Override
        void completion() {
            done = true;
            if (wip.getAndIncrement() == 0) {
                emit();
                downstream.onComplete();
            }
        }

        @Override
        void run() {
            if (wip.getAndIncrement() == 0) {
                do {
                    boolean d = done;
                    emit();
                    if (d) {
                        downstream.onComplete();
                        return;
                    }
                } while (wip.decrementAndGet() != 0);
            }
        }
    }
}