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.AtomicReference;

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.util.*;
import io.reactivex.plugins.RxJavaPlugins;

Maps the upstream values into CompletableSources, subscribes to the newer one while disposing the subscription to the previous CompletableSource, thus keeping at most one active CompletableSource running. 
History: 2.1.11 - experimental
Type parameters:
<T> – the upstream value type
Since:
2.2/**
 * Maps the upstream values into {@link CompletableSource}s, subscribes to the newer one while
 * disposing the subscription to the previous {@code CompletableSource}, thus keeping at most one
 * active {@code CompletableSource} running.
 * <p>History: 2.1.11 - experimental
 * @param <T> the upstream value type
 * @since 2.2
 */
public final class ObservableSwitchMapCompletable<T> extends Completable {

    final Observable<T> source;

    final Function<? super T, ? extends CompletableSource> mapper;

    final boolean delayErrors;

    public ObservableSwitchMapCompletable(Observable<T> source,
            Function<? super T, ? extends CompletableSource> mapper, boolean delayErrors) {
        this.source = source;
        this.mapper = mapper;
        this.delayErrors = delayErrors;
    }

    @Override
    protected void subscribeActual(CompletableObserver observer) {
        if (!ScalarXMapZHelper.tryAsCompletable(source, mapper, observer)) {
            source.subscribe(new SwitchMapCompletableObserver<T>(observer, mapper, delayErrors));
        }
    }

    static final class SwitchMapCompletableObserver<T> implements Observer<T>, Disposable {

        final CompletableObserver downstream;

        final Function<? super T, ? extends CompletableSource> mapper;

        final boolean delayErrors;

        final AtomicThrowable errors;

        final AtomicReference<SwitchMapInnerObserver> inner;

        static final SwitchMapInnerObserver INNER_DISPOSED = new SwitchMapInnerObserver(null);

        volatile boolean done;

        Disposable upstream;

        SwitchMapCompletableObserver(CompletableObserver downstream,
                Function<? super T, ? extends CompletableSource> mapper, boolean delayErrors) {
            this.downstream = downstream;
            this.mapper = mapper;
            this.delayErrors = delayErrors;
            this.errors = new AtomicThrowable();
            this.inner = new AtomicReference<SwitchMapInnerObserver>();
        }

        @Override
        public void onSubscribe(Disposable d) {
            if (DisposableHelper.validate(upstream, d)) {
                this.upstream = d;
                downstream.onSubscribe(this);
            }
        }

        @Override
        public void onNext(T t) {
            CompletableSource c;

            try {
                c = ObjectHelper.requireNonNull(mapper.apply(t), "The mapper returned a null CompletableSource");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                upstream.dispose();
                onError(ex);
                return;
            }

            SwitchMapInnerObserver o = new SwitchMapInnerObserver(this);

            for (;;) {
                SwitchMapInnerObserver current = inner.get();
                if (current == INNER_DISPOSED) {
                    break;
                }
                if (inner.compareAndSet(current, o)) {
                    if (current != null) {
                        current.dispose();
                    }
                    c.subscribe(o);
                    break;
                }
            }
        }

        @Override
        public void onError(Throwable t) {
            if (errors.addThrowable(t)) {
                if (delayErrors) {
                    onComplete();
                } else {
                    disposeInner();
                    Throwable ex = errors.terminate();
                    if (ex != ExceptionHelper.TERMINATED) {
                        downstream.onError(ex);
                    }
                }
            } else {
                RxJavaPlugins.onError(t);
            }
        }

        @Override
        public void onComplete() {
            done = true;
            if (inner.get() == null) {
                Throwable ex = errors.terminate();
                if (ex == null) {
                    downstream.onComplete();
                } else {
                    downstream.onError(ex);
                }
            }
        }

        void disposeInner() {
            SwitchMapInnerObserver o = inner.getAndSet(INNER_DISPOSED);
            if (o != null && o != INNER_DISPOSED) {
                o.dispose();
            }
        }

        @Override
        public void dispose() {
            upstream.dispose();
            disposeInner();
        }

        @Override
        public boolean isDisposed() {
            return inner.get() == INNER_DISPOSED;
        }

        void innerError(SwitchMapInnerObserver sender, Throwable error) {
            if (inner.compareAndSet(sender, null)) {
                if (errors.addThrowable(error)) {
                    if (delayErrors) {
                        if (done) {
                            Throwable ex = errors.terminate();
                            downstream.onError(ex);
                        }
                    } else {
                        dispose();
                        Throwable ex = errors.terminate();
                        if (ex != ExceptionHelper.TERMINATED) {
                            downstream.onError(ex);
                        }
                    }
                    return;
                }
            }
            RxJavaPlugins.onError(error);
        }

        void innerComplete(SwitchMapInnerObserver sender) {
            if (inner.compareAndSet(sender, null)) {
                if (done) {
                    Throwable ex = errors.terminate();
                    if (ex == null) {
                        downstream.onComplete();
                    } else {
                        downstream.onError(ex);
                    }
                }
            }
        }

        static final class SwitchMapInnerObserver extends AtomicReference<Disposable>
        implements CompletableObserver {

            private static final long serialVersionUID = -8003404460084760287L;

            final SwitchMapCompletableObserver<?> parent;

            SwitchMapInnerObserver(SwitchMapCompletableObserver<?> parent) {
                this.parent = parent;
            }

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

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

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

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