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.*;
import io.reactivex.internal.disposables.DisposableHelper;
import io.reactivex.internal.functions.ObjectHelper;

Maps a source item to another MaybeSource then calls a BiFunction with the
original item and the secondary item to generate the final result.
Type parameters:
<T> – the main value type
<U> – the second value type
<R> – the result value type/**
 * Maps a source item to another MaybeSource then calls a BiFunction with the
 * original item and the secondary item to generate the final result.
 * 
 * @param <T> the main value type
 * @param <U> the second value type
 * @param <R> the result value type
 */
public final class MaybeFlatMapBiSelector<T, U, R> extends AbstractMaybeWithUpstream<T, R> {

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

    final BiFunction<? super T, ? super U, ? extends R> resultSelector;

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

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

    static final class FlatMapBiMainObserver<T, U, R>
    implements MaybeObserver<T>, Disposable {

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

        final InnerObserver<T, U, R> inner;

        FlatMapBiMainObserver(MaybeObserver<? super R> actual,
                Function<? super T, ? extends MaybeSource<? extends U>> mapper,
                BiFunction<? super T, ? super U, ? extends R> resultSelector) {
            this.inner = new InnerObserver<T, U, R>(actual, resultSelector);
            this.mapper = mapper;
        }

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

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

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

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

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

            if (DisposableHelper.replace(inner, null)) {
                inner.value = value;
                next.subscribe(inner);
            }
        }

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

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

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

            private static final long serialVersionUID = -2897979525538174559L;

            final MaybeObserver<? super R> downstream;

            final BiFunction<? super T, ? super U, ? extends R> resultSelector;

            T value;

            InnerObserver(MaybeObserver<? super R> actual,
                    BiFunction<? super T, ? super U, ? extends R> resultSelector) {
                this.downstream = actual;
                this.resultSelector = resultSelector;
            }

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

            @Override
            public void onSuccess(U value) {
                T t = this.value;
                this.value = null;

                R r;

                try {
                    r = ObjectHelper.requireNonNull(resultSelector.apply(t, value), "The resultSelector returned a null value");
                } catch (Throwable ex) {
                    Exceptions.throwIfFatal(ex);
                    downstream.onError(ex);
                    return;
                }

                downstream.onSuccess(r);
            }

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

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