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.concurrent.atomic.AtomicReference;

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;

Maps a value into a MaybeSource and relays its signal.
Type parameters:
<T> – the source value type
<R> – the result value type/**
 * Maps a value into a MaybeSource and relays its signal.
 *
 * @param <T> the source value type
 * @param <R> the result value type
 */
public final class MaybeFlatten<T, R> extends AbstractMaybeWithUpstream<T, R> {

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

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

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

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

        private static final long serialVersionUID = 4375739915521278546L;

        final MaybeObserver<? super R> downstream;

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

        Disposable upstream;

        FlatMapMaybeObserver(MaybeObserver<? super R> actual,
                Function<? super T, ? extends MaybeSource<? extends R>> mapper) {
            this.downstream = actual;
            this.mapper = mapper;
        }

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

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

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

                downstream.onSubscribe(this);
            }
        }

        @Override
        public void onSuccess(T value) {
            MaybeSource<? extends R> source;

            try {
                source = ObjectHelper.requireNonNull(mapper.apply(value), "The mapper returned a null MaybeSource");
            } catch (Exception ex) {
                Exceptions.throwIfFatal(ex);
                downstream.onError(ex);
                return;
            }

            if (!isDisposed()) {
                source.subscribe(new InnerObserver());
            }
        }

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

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

        final class InnerObserver implements MaybeObserver<R> {

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

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

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

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