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.single;

import java.util.Iterator;
import java.util.concurrent.atomic.AtomicLong;

import io.reactivex.annotations.Nullable;
import org.reactivestreams.Subscriber;

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.*;
import io.reactivex.internal.util.BackpressureHelper;

Maps a success value into an Iterable and streams it back as a Flowable.
Type parameters:
<T> – the source value type
<R> – the element type of the Iterable/**
 * Maps a success value into an Iterable and streams it back as a Flowable.
 *
 * @param <T> the source value type
 * @param <R> the element type of the Iterable
 */
public final class SingleFlatMapIterableFlowable<T, R> extends Flowable<R> {

    final SingleSource<T> source;

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

    public SingleFlatMapIterableFlowable(SingleSource<T> source,
            Function<? super T, ? extends Iterable<? extends R>> mapper) {
        this.source = source;
        this.mapper = mapper;
    }

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

    static final class FlatMapIterableObserver<T, R>
    extends BasicIntQueueSubscription<R>
    implements SingleObserver<T> {

        private static final long serialVersionUID = -8938804753851907758L;

        final Subscriber<? super R> downstream;

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

        final AtomicLong requested;

        Disposable upstream;

        volatile Iterator<? extends R> it;

        volatile boolean cancelled;

        boolean outputFused;

        FlatMapIterableObserver(Subscriber<? super R> actual,
                Function<? super T, ? extends Iterable<? extends R>> mapper) {
            this.downstream = actual;
            this.mapper = mapper;
            this.requested = new AtomicLong();
        }

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

                downstream.onSubscribe(this);
            }
        }

        @Override
        public void onSuccess(T value) {
            Iterator<? extends R> iterator;
            boolean has;
            try {
                iterator = mapper.apply(value).iterator();

                has = iterator.hasNext();
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                downstream.onError(ex);
                return;
            }

            if (!has) {
                downstream.onComplete();
                return;
            }

            this.it = iterator;
            drain();
        }

        @Override
        public void onError(Throwable e) {
            upstream = DisposableHelper.DISPOSED;
            downstream.onError(e);
        }

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

        @Override
        public void cancel() {
            cancelled = true;
            upstream.dispose();
            upstream = DisposableHelper.DISPOSED;
        }

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

            Subscriber<? super R> a = downstream;
            Iterator<? extends R> iterator = this.it;

            if (outputFused && iterator != null) {
                a.onNext(null);
                a.onComplete();
                return;
            }

            int missed = 1;

            for (;;) {

                if (iterator != null) {
                    long r = requested.get();
                    long e = 0L;

                    if (r == Long.MAX_VALUE) {
                        slowPath(a, iterator);
                        return;
                    }

                    while (e != r) {
                        if (cancelled) {
                            return;
                        }

                        R v;

                        try {
                            v = ObjectHelper.requireNonNull(iterator.next(), "The iterator returned a null value");
                        } catch (Throwable ex) {
                            Exceptions.throwIfFatal(ex);
                            a.onError(ex);
                            return;
                        }

                        a.onNext(v);

                        if (cancelled) {
                            return;
                        }

                        e++;

                        boolean b;

                        try {
                            b = iterator.hasNext();
                        } catch (Throwable ex) {
                            Exceptions.throwIfFatal(ex);
                            a.onError(ex);
                            return;
                        }

                        if (!b) {
                            a.onComplete();
                            return;
                        }
                    }

                    if (e != 0L) {
                        BackpressureHelper.produced(requested, e);
                    }
                }

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

                if (iterator == null) {
                    iterator = it;
                }
            }
        }

        void slowPath(Subscriber<? super R> a, Iterator<? extends R> iterator) {
            for (;;) {
                if (cancelled) {
                    return;
                }

                R v;

                try {
                    v = iterator.next();
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    a.onError(ex);
                    return;
                }

                a.onNext(v);

                if (cancelled) {
                    return;
                }

                boolean b;

                try {
                    b = iterator.hasNext();
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    a.onError(ex);
                    return;
                }

                if (!b) {
                    a.onComplete();
                    return;
                }
            }
        }

        @Override
        public int requestFusion(int mode) {
            if ((mode & ASYNC) != 0) {
                outputFused = true;
                return ASYNC;
            }
            return NONE;
        }

        @Override
        public void clear() {
            it = null;
        }

        @Override
        public boolean isEmpty() {
            return it == null;
        }

        @Nullable
        @Override
        public R poll() throws Exception {
            Iterator<? extends R> iterator = it;

            if (iterator != null) {
                R v = ObjectHelper.requireNonNull(iterator.next(), "The iterator returned a null value");
                if (!iterator.hasNext()) {
                    it = null;
                }
                return v;
            }
            return null;
        }

    }
}