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.mixed;

import java.util.concurrent.atomic.*;

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.Function;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.*;
import io.reactivex.plugins.RxJavaPlugins;

Maps the upstream items into SingleSources and switches (subscribes) to the newer ones while disposing the older ones and emits the latest success value, optionally delaying errors from the main source or the inner sources. 
History: 2.1.11 - experimental
Type parameters:
<T> – the upstream value type
<R> – the downstream value type
Since:
2.2/**
 * Maps the upstream items into {@link SingleSource}s and switches (subscribes) to the newer ones
 * while disposing the older ones and emits the latest success value, optionally delaying
 * errors from the main source or the inner sources.
 * <p>History: 2.1.11 - experimental
 * @param <T> the upstream value type
 * @param <R> the downstream value type
 * @since 2.2
 */
public final class FlowableSwitchMapSingle<T, R> extends Flowable<R> {

    final Flowable<T> source;

    final Function<? super T, ? extends SingleSource<? extends R>> mapper;

    final boolean delayErrors;

    public FlowableSwitchMapSingle(Flowable<T> source,
            Function<? super T, ? extends SingleSource<? extends R>> mapper,
            boolean delayErrors) {
        this.source = source;
        this.mapper = mapper;
        this.delayErrors = delayErrors;
    }

    @Override
    protected void subscribeActual(Subscriber<? super R> s) {
        source.subscribe(new SwitchMapSingleSubscriber<T, R>(s, mapper, delayErrors));
    }

    static final class SwitchMapSingleSubscriber<T, R> extends AtomicInteger
    implements FlowableSubscriber<T>, Subscription {

        private static final long serialVersionUID = -5402190102429853762L;

        final Subscriber<? super R> downstream;

        final Function<? super T, ? extends SingleSource<? extends R>> mapper;

        final boolean delayErrors;

        final AtomicThrowable errors;

        final AtomicLong requested;

        final AtomicReference<SwitchMapSingleObserver<R>> inner;

        static final SwitchMapSingleObserver<Object> INNER_DISPOSED =
                new SwitchMapSingleObserver<Object>(null);

        Subscription upstream;

        volatile boolean done;

        volatile boolean cancelled;

        long emitted;

        SwitchMapSingleSubscriber(Subscriber<? super R> downstream,
                Function<? super T, ? extends SingleSource<? extends R>> mapper,
                boolean delayErrors) {
            this.downstream = downstream;
            this.mapper = mapper;
            this.delayErrors = delayErrors;
            this.errors = new AtomicThrowable();
            this.requested = new AtomicLong();
            this.inner = new AtomicReference<SwitchMapSingleObserver<R>>();
        }

        @Override
        public void onSubscribe(Subscription s) {
            if (SubscriptionHelper.validate(upstream, s)) {
                upstream = s;
                downstream.onSubscribe(this);
                s.request(Long.MAX_VALUE);
            }
        }

        @Override
        @SuppressWarnings({ "unchecked", "rawtypes" })
        public void onNext(T t) {
            SwitchMapSingleObserver<R> current = inner.get();
            if (current != null) {
                current.dispose();
            }

            SingleSource<? extends R> ss;

            try {
                ss = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper returned a null SingleSource");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                upstream.cancel();
                inner.getAndSet((SwitchMapSingleObserver)INNER_DISPOSED);
                onError(ex);
                return;
            }

            SwitchMapSingleObserver<R> observer = new SwitchMapSingleObserver<R>(this);

            for (;;) {
                current = inner.get();
                if (current == INNER_DISPOSED) {
                    break;
                }
                if (inner.compareAndSet(current, observer)) {
                    ss.subscribe(observer);
                    break;
                }
            }
        }

        @Override
        public void onError(Throwable t) {
            if (errors.addThrowable(t)) {
                if (!delayErrors) {
                    disposeInner();
                }
                done = true;
                drain();
            } else {
                RxJavaPlugins.onError(t);
            }
        }

        @Override
        public void onComplete() {
            done = true;
            drain();
        }

        @SuppressWarnings({ "unchecked", "rawtypes" })
        void disposeInner() {
            SwitchMapSingleObserver<R> current = inner.getAndSet((SwitchMapSingleObserver)INNER_DISPOSED);
            if (current != null && current != INNER_DISPOSED) {
                current.dispose();
            }
        }

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

        @Override
        public void cancel() {
            cancelled = true;
            upstream.cancel();
            disposeInner();
        }

        void innerError(SwitchMapSingleObserver<R> sender, Throwable ex) {
            if (inner.compareAndSet(sender, null)) {
                if (errors.addThrowable(ex)) {
                    if (!delayErrors) {
                        upstream.cancel();
                        disposeInner();
                    }
                    drain();
                    return;
                }
            }
            RxJavaPlugins.onError(ex);
        }

        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }

            int missed = 1;
            Subscriber<? super R> downstream = this.downstream;
            AtomicThrowable errors = this.errors;
            AtomicReference<SwitchMapSingleObserver<R>> inner = this.inner;
            AtomicLong requested = this.requested;
            long emitted = this.emitted;

            for (;;) {

                for (;;) {
                    if (cancelled) {
                        return;
                    }

                    if (errors.get() != null) {
                        if (!delayErrors) {
                            Throwable ex = errors.terminate();
                            downstream.onError(ex);
                            return;
                        }
                    }

                    boolean d = done;
                    SwitchMapSingleObserver<R> current = inner.get();
                    boolean empty = current == null;

                    if (d && empty) {
                        Throwable ex = errors.terminate();
                        if (ex != null) {
                            downstream.onError(ex);
                        } else {
                            downstream.onComplete();
                        }
                        return;
                    }

                    if (empty || current.item == null || emitted == requested.get()) {
                        break;
                    }

                    inner.compareAndSet(current, null);

                    downstream.onNext(current.item);

                    emitted++;
                }

                this.emitted = emitted;
                missed = addAndGet(-missed);
                if (missed == 0) {
                    break;
                }
            }
        }

        static final class SwitchMapSingleObserver<R>
        extends AtomicReference<Disposable> implements SingleObserver<R> {

            private static final long serialVersionUID = 8042919737683345351L;

            final SwitchMapSingleSubscriber<?, R> parent;

            volatile R item;

            SwitchMapSingleObserver(SwitchMapSingleSubscriber<?, R> parent) {
                this.parent = parent;
            }

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

            @Override
            public void onSuccess(R t) {
                item = t;
                parent.drain();
            }

            @Override
            public void onError(Throwable e) {
                parent.innerError(this, e);
            }

            void dispose() {
                DisposableHelper.dispose(this);
            }
        }
    }
}