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.observable;

import java.util.concurrent.atomic.*;

import io.reactivex.*;
import io.reactivex.disposables.*;
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.queue.SpscLinkedArrayQueue;
import io.reactivex.internal.util.AtomicThrowable;
import io.reactivex.plugins.RxJavaPlugins;

Maps upstream values into SingleSources and merges their signals into one sequence.
Type parameters:
<T> – the source value type
<R> – the result value type/**
 * Maps upstream values into SingleSources and merges their signals into one sequence.
 * @param <T> the source value type
 * @param <R> the result value type
 */
public final class ObservableFlatMapSingle<T, R> extends AbstractObservableWithUpstream<T, R> {

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

    final boolean delayErrors;

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

    @Override
    protected void subscribeActual(Observer<? super R> observer) {
        source.subscribe(new FlatMapSingleObserver<T, R>(observer, mapper, delayErrors));
    }

    static final class FlatMapSingleObserver<T, R>
    extends AtomicInteger
    implements Observer<T>, Disposable {

        private static final long serialVersionUID = 8600231336733376951L;

        final Observer<? super R> downstream;

        final boolean delayErrors;

        final CompositeDisposable set;

        final AtomicInteger active;

        final AtomicThrowable errors;

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

        final AtomicReference<SpscLinkedArrayQueue<R>> queue;

        Disposable upstream;

        volatile boolean cancelled;

        FlatMapSingleObserver(Observer<? super R> actual,
                Function<? super T, ? extends SingleSource<? extends R>> mapper, boolean delayErrors) {
            this.downstream = actual;
            this.mapper = mapper;
            this.delayErrors = delayErrors;
            this.set = new CompositeDisposable();
            this.errors = new AtomicThrowable();
            this.active = new AtomicInteger(1);
            this.queue = new AtomicReference<SpscLinkedArrayQueue<R>>();
        }

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

                downstream.onSubscribe(this);
            }
        }

        @Override
        public void onNext(T t) {
            SingleSource<? extends R> ms;

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

            active.getAndIncrement();

            InnerObserver inner = new InnerObserver();

            if (!cancelled && set.add(inner)) {
                ms.subscribe(inner);
            }
        }

        @Override
        public void onError(Throwable t) {
            active.decrementAndGet();
            if (errors.addThrowable(t)) {
                if (!delayErrors) {
                    set.dispose();
                }
                drain();
            } else {
                RxJavaPlugins.onError(t);
            }
        }

        @Override
        public void onComplete() {
            active.decrementAndGet();
            drain();
        }

        @Override
        public void dispose() {
            cancelled = true;
            upstream.dispose();
            set.dispose();
        }

        @Override
        public boolean isDisposed() {
            return cancelled;
        }

        void innerSuccess(InnerObserver inner, R value) {
            set.delete(inner);
            if (get() == 0 && compareAndSet(0, 1)) {
                downstream.onNext(value);

                boolean d = active.decrementAndGet() == 0;
                SpscLinkedArrayQueue<R> q = queue.get();

                if (d && (q == null || q.isEmpty())) {
                    Throwable ex = errors.terminate();
                    if (ex != null) {
                        downstream.onError(ex);
                    } else {
                        downstream.onComplete();
                    }
                    return;
                }
                if (decrementAndGet() == 0) {
                    return;
                }
            } else {
                SpscLinkedArrayQueue<R> q = getOrCreateQueue();
                synchronized (q) {
                    q.offer(value);
                }
                active.decrementAndGet();
                if (getAndIncrement() != 0) {
                    return;
                }
            }
            drainLoop();
        }

        SpscLinkedArrayQueue<R> getOrCreateQueue() {
            for (;;) {
                SpscLinkedArrayQueue<R> current = queue.get();
                if (current != null) {
                    return current;
                }
                current = new SpscLinkedArrayQueue<R>(Observable.bufferSize());
                if (queue.compareAndSet(null, current)) {
                    return current;
                }
            }
        }

        void innerError(InnerObserver inner, Throwable e) {
            set.delete(inner);
            if (errors.addThrowable(e)) {
                if (!delayErrors) {
                    upstream.dispose();
                    set.dispose();
                }
                active.decrementAndGet();
                drain();
            } else {
                RxJavaPlugins.onError(e);
            }
        }

        void drain() {
            if (getAndIncrement() == 0) {
                drainLoop();
            }
        }

        void clear() {
            SpscLinkedArrayQueue<R> q = queue.get();
            if (q != null) {
                q.clear();
            }
        }

        void drainLoop() {
            int missed = 1;
            Observer<? super R> a = downstream;
            AtomicInteger n = active;
            AtomicReference<SpscLinkedArrayQueue<R>> qr = queue;

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

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

                    boolean d = n.get() == 0;
                    SpscLinkedArrayQueue<R> q = qr.get();
                    R v = q != null ? q.poll() : null;
                    boolean empty = v == null;

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

                    if (empty) {
                        break;
                    }

                    a.onNext(v);
                }

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

        final class InnerObserver extends AtomicReference<Disposable>
        implements SingleObserver<R>, Disposable {
            private static final long serialVersionUID = -502562646270949838L;

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

            @Override
            public void onSuccess(R value) {
                innerSuccess(this, value);
            }

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

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

            @Override
            public void dispose() {
                DisposableHelper.dispose(this);
            }
        }
    }
}