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.observable;

import java.util.concurrent.atomic.AtomicReference;

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

Subscribe to a main Observable first, then when it completes normally, subscribe to a Single,
signal its success value followed by a completion or signal its error as is.
History: 2.1.10 - experimental
Type parameters:
<T> – the element type of the main source and output type
Since:
2.2/**
 * Subscribe to a main Observable first, then when it completes normally, subscribe to a Single,
 * signal its success value followed by a completion or signal its error as is.
 * <p>History: 2.1.10 - experimental
 * @param <T> the element type of the main source and output type
 * @since 2.2
 */
public final class ObservableConcatWithSingle<T> extends AbstractObservableWithUpstream<T, T> {

    final SingleSource<? extends T> other;

    public ObservableConcatWithSingle(Observable<T> source, SingleSource<? extends T> other) {
        super(source);
        this.other = other;
    }

    @Override
    protected void subscribeActual(Observer<? super T> observer) {
        source.subscribe(new ConcatWithObserver<T>(observer, other));
    }

    static final class ConcatWithObserver<T>
    extends AtomicReference<Disposable>
    implements Observer<T>, SingleObserver<T>, Disposable {

        private static final long serialVersionUID = -1953724749712440952L;

        final Observer<? super T> downstream;

        SingleSource<? extends T> other;

        boolean inSingle;

        ConcatWithObserver(Observer<? super T> actual, SingleSource<? extends T> other) {
            this.downstream = actual;
            this.other = other;
        }

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

        @Override
        public void onNext(T t) {
            downstream.onNext(t);
        }

        @Override
        public void onSuccess(T t) {
            downstream.onNext(t);
            downstream.onComplete();
        }

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

        @Override
        public void onComplete() {
            inSingle = true;
            DisposableHelper.replace(this, null);
            SingleSource<? extends T> ss = other;
            other = null;
            ss.subscribe(this);
        }

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

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