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 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.
Type parameters:
<T> – the input value type
<R> – the result value type/**
 * Maps the success value of the source MaybeSource into a Single.
 * @param <T> the input value type
 * @param <R> the result value type
 */
public final class MaybeFlatMapSingle<T, R> extends Single<R> {

    final MaybeSource<T> source;

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

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

    @Override
    protected void subscribeActual(SingleObserver<? super R> downstream) {
        source.subscribe(new FlatMapMaybeObserver<T, R>(downstream, mapper));
    }

    static final class FlatMapMaybeObserver<T, R>
    extends AtomicReference<Disposable>
    implements MaybeObserver<T>, Disposable {

        private static final long serialVersionUID = 4827726964688405508L;

        final SingleObserver<? super R> downstream;

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

        FlatMapMaybeObserver(SingleObserver<? super R> actual, Function<? super T, ? extends SingleSource<? extends R>> 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<? extends R> 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<R>(this, downstream));
            }
        }

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

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

    static final class FlatMapSingleObserver<R> implements SingleObserver<R> {

        final AtomicReference<Disposable> parent;

        final SingleObserver<? super R> downstream;

        FlatMapSingleObserver(AtomicReference<Disposable> parent, SingleObserver<? super R> 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);
        }
    }
}