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 io.reactivex.*;
import io.reactivex.annotations.Nullable;
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.observers.BasicIntQueueDisposable;

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

    final SingleSource<T> source;

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

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

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

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

        private static final long serialVersionUID = -8938804753851907758L;

        final Observer<? super R> downstream;

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

        Disposable upstream;

        volatile Iterator<? extends R> it;

        volatile boolean cancelled;

        boolean outputFused;

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

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

                downstream.onSubscribe(this);
            }
        }

        @Override
        public void onSuccess(T value) {
            Observer<? super R> a = downstream;
            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) {
                a.onComplete();
                return;
            }

            if (outputFused) {
                it = iterator;
                a.onNext(null);
                a.onComplete();
            } else {
                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 void onError(Throwable e) {
            upstream = DisposableHelper.DISPOSED;
            downstream.onError(e);
        }

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

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

        @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;
        }

    }
}