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Reactive Extensions for Java
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/**
 * 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 io.reactivex.MaybeObserver;
import io.reactivex.MaybeSource;
import io.reactivex.Single;
import io.reactivex.SingleObserver;
import io.reactivex.SingleSource;
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 java.util.NoSuchElementException;
import java.util.concurrent.atomic.AtomicReference;

/**
 * Maps the success value of the source MaybeSource into a Single.
 * @param  the input value type
 * @param  the result value type
 */
public final class MaybeFlatMapSingle extends Single {

    final MaybeSource source;

    final Function> mapper;

    public MaybeFlatMapSingle(MaybeSource source, Function> mapper) {
        this.source = source;
        this.mapper = mapper;
    }

    @Override
    protected void subscribeActual(SingleObserver downstream) {
        source.subscribe(new FlatMapMaybeObserver(downstream, mapper));
    }

    static final class FlatMapMaybeObserver
    extends AtomicReference
    implements MaybeObserver, Disposable {

        private static final long serialVersionUID = 4827726964688405508L;

        final SingleObserver downstream;

        final Function> mapper;

        FlatMapMaybeObserver(SingleObserver actual, Function> mapper) {
            this.downstream = actual;
            this.mapper = mapper;
        }

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

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

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

        @Override
        public void onSuccess(T value) {
            SingleSource ss;

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

            if (!isDisposed()) {
                ss.subscribe(new FlatMapSingleObserver(this, downstream));
            }
        }

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

        @Override
        public void onComplete() {
            downstream.onError(new NoSuchElementException());
        }
    }

    static final class FlatMapSingleObserver implements SingleObserver {

        final AtomicReference parent;

        final SingleObserver downstream;

        FlatMapSingleObserver(AtomicReference parent, SingleObserver downstream) {
            this.parent = parent;
            this.downstream = downstream;
        }

        @Override
        public void onSubscribe(final Disposable d) {
            DisposableHelper.replace(parent, d);
        }

        @Override
        public void onSuccess(final R value) {
            downstream.onSuccess(value);
        }

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