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.maybe;

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

import org.reactivestreams.*;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.internal.disposables.SequentialDisposable;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.internal.util.*;

Concatenate values of each MaybeSource provided by an Iterable.
Type parameters:
<T> – the value type/**
 * Concatenate values of each MaybeSource provided by an Iterable.
 *
 * @param <T> the value type
 */
public final class MaybeConcatIterable<T> extends Flowable<T> {

    final Iterable<? extends MaybeSource<? extends T>> sources;

    public MaybeConcatIterable(Iterable<? extends MaybeSource<? extends T>> sources) {
        this.sources = sources;
    }

    @Override
    protected void subscribeActual(Subscriber<? super T> s) {

        Iterator<? extends MaybeSource<? extends T>> it;

        try {
            it = ObjectHelper.requireNonNull(sources.iterator(), "The sources Iterable returned a null Iterator");
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            EmptySubscription.error(ex, s);
            return;
        }

        ConcatMaybeObserver<T> parent = new ConcatMaybeObserver<T>(s, it);
        s.onSubscribe(parent);
        parent.drain();
    }

    static final class ConcatMaybeObserver<T>
    extends AtomicInteger
    implements MaybeObserver<T>, Subscription {

        private static final long serialVersionUID = 3520831347801429610L;

        final Subscriber<? super T> downstream;

        final AtomicLong requested;

        final AtomicReference<Object> current;

        final SequentialDisposable disposables;

        final Iterator<? extends MaybeSource<? extends T>> sources;

        long produced;

        ConcatMaybeObserver(Subscriber<? super T> actual, Iterator<? extends MaybeSource<? extends T>> sources) {
            this.downstream = actual;
            this.sources = sources;
            this.requested = new AtomicLong();
            this.disposables = new SequentialDisposable();
            this.current = new AtomicReference<Object>(NotificationLite.COMPLETE); // as if a previous completed
        }

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

        @Override
        public void cancel() {
            disposables.dispose();
        }

        @Override
        public void onSubscribe(Disposable d) {
            disposables.replace(d);
        }

        @Override
        public void onSuccess(T value) {
            current.lazySet(value);
            drain();
        }

        @Override
        public void onError(Throwable e) {
            downstream.onError(e);
        }

        @Override
        public void onComplete() {
            current.lazySet(NotificationLite.COMPLETE);
            drain();
        }

        @SuppressWarnings("unchecked")
        void drain() {
            if (getAndIncrement() != 0) {
                return;
            }

            AtomicReference<Object> c = current;
            Subscriber<? super T> a = downstream;
            Disposable cancelled = disposables;

            for (;;) {
                if (cancelled.isDisposed()) {
                    c.lazySet(null);
                    return;
                }

                Object o = c.get();

                if (o != null) {
                    boolean goNextSource;
                    if (o != NotificationLite.COMPLETE) {
                        long p = produced;
                        if (p != requested.get()) {
                            produced = p + 1;
                            c.lazySet(null);
                            goNextSource = true;

                            a.onNext((T)o);
                        } else {
                            goNextSource = false;
                        }
                    } else {
                        goNextSource = true;
                        c.lazySet(null);
                    }

                    if (goNextSource && !cancelled.isDisposed()) {
                        boolean b;

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

                        if (b) {
                            MaybeSource<? extends T> source;

                            try {
                                source = ObjectHelper.requireNonNull(sources.next(), "The source Iterator returned a null MaybeSource");
                            } catch (Throwable ex) {
                                Exceptions.throwIfFatal(ex);
                                a.onError(ex);
                                return;
                            }

                            source.subscribe(this);
                        } else {
                            a.onComplete();
                        }
                    }
                }

                if (decrementAndGet() == 0) {
                    break;
                }
            }
        }
    }
}