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.maybe;

import java.util.concurrent.atomic.AtomicReference;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.plugins.RxJavaPlugins;

Delay the subscription to the main Maybe until the other signals an item or completes.
Type parameters:
<T> – the main value type
<U> – the other value type/**
 * Delay the subscription to the main Maybe until the other signals an item or completes.
 * 
 * @param <T> the main value type
 * @param <U> the other value type
 */
public final class MaybeDelaySubscriptionOtherPublisher<T, U> extends AbstractMaybeWithUpstream<T, T> {

    final Publisher<U> other;

    public MaybeDelaySubscriptionOtherPublisher(MaybeSource<T> source, Publisher<U> other) {
        super(source);
        this.other = other;
    }

    @Override
    protected void subscribeActual(MaybeObserver<? super T> observer) {
        other.subscribe(new OtherSubscriber<T>(observer, source));
    }

    static final class OtherSubscriber<T> implements FlowableSubscriber<Object>, Disposable {
        final DelayMaybeObserver<T> main;

        MaybeSource<T> source;

        Subscription upstream;

        OtherSubscriber(MaybeObserver<? super T> actual, MaybeSource<T> source) {
            this.main = new DelayMaybeObserver<T>(actual);
            this.source = source;
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(this.upstream, s)) {
                this.upstream = s;

                main.downstream.onSubscribe(this);

                s.request(Long.MAX_VALUE);
            }
        }

        @Override
        public void onNext(Object t) {
            if (upstream != SubscriptionHelper.CANCELLED) {
                upstream.cancel();
                upstream = SubscriptionHelper.CANCELLED;

                subscribeNext();
            }
        }

        @Override
        public void onError(Throwable t) {
            if (upstream != SubscriptionHelper.CANCELLED) {
                upstream = SubscriptionHelper.CANCELLED;

                main.downstream.onError(t);
            } else {
                RxJavaPlugins.onError(t);
            }
        }

        @Override
        public void onComplete() {
            if (upstream != SubscriptionHelper.CANCELLED) {
                upstream = SubscriptionHelper.CANCELLED;

                subscribeNext();
            }
        }

        void subscribeNext() {
            MaybeSource<T> src = source;
            source = null;

            src.subscribe(main);
        }

        @Override
        public boolean isDisposed() {
            return DisposableHelper.isDisposed(main.get());
        }

        @Override
        public void dispose() {
            upstream.cancel();
            upstream = SubscriptionHelper.CANCELLED;
            DisposableHelper.dispose(main);
        }
    }

    static final class DelayMaybeObserver<T> extends AtomicReference<Disposable>
    implements MaybeObserver<T> {

        private static final long serialVersionUID = 706635022205076709L;

        final MaybeObserver<? super T> downstream;

        DelayMaybeObserver(MaybeObserver<? super T> downstream) {
            this.downstream = downstream;
        }

        @Override
        public void onSubscribe(Disposable d) {
            DisposableHelper.setOnce(this, d);
        }

        @Override
        public void onSuccess(T value) {
            downstream.onSuccess(value);
        }

        @Override
        public void onError(Throwable e) {
            downstream.onError(e);
        }

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