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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.observable;

import io.reactivex.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.SequentialDisposable;

public final class ObservableSwitchIfEmpty extends AbstractObservableWithUpstream {
    final ObservableSource other;
    public ObservableSwitchIfEmpty(ObservableSource source, ObservableSource other) {
        super(source);
        this.other = other;
    }

    @Override
    public void subscribeActual(Observer t) {
        SwitchIfEmptyObserver parent = new SwitchIfEmptyObserver(t, other);
        t.onSubscribe(parent.arbiter);
        source.subscribe(parent);
    }

    static final class SwitchIfEmptyObserver implements Observer {
        final Observer downstream;
        final ObservableSource other;
        final SequentialDisposable arbiter;

        boolean empty;

        SwitchIfEmptyObserver(Observer actual, ObservableSource other) {
            this.downstream = actual;
            this.other = other;
            this.empty = true;
            this.arbiter = new SequentialDisposable();
        }

        @Override
        public void onSubscribe(Disposable d) {
            arbiter.update(d);
        }

        @Override
        public void onNext(T t) {
            if (empty) {
                empty = false;
            }
            downstream.onNext(t);
        }

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

        @Override
        public void onComplete() {
            if (empty) {
                empty = false;
                other.subscribe(this);
            } else {
                downstream.onComplete();
            }
        }
    }
}