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.observers;

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

A fuseable Observer that can generate 0 or 1 resulting value.
Type parameters:
<T> – the input value type
<R> – the output value type/**
 * A fuseable Observer that can generate 0 or 1 resulting value.
 * @param <T> the input value type
 * @param <R> the output value type
 */
public abstract class DeferredScalarObserver<T, R>
extends DeferredScalarDisposable<R>
implements Observer<T> {

    private static final long serialVersionUID = -266195175408988651L;

    
The upstream disposable. /** The upstream disposable. */
    protected Disposable upstream;

    
Creates a DeferredScalarObserver instance and wraps a downstream Observer.
Params:
downstream – the downstream subscriber, not null (not verified)/**
     * Creates a DeferredScalarObserver instance and wraps a downstream Observer.
     * @param downstream the downstream subscriber, not null (not verified)
     */
    public DeferredScalarObserver(Observer<? super R> downstream) {
        super(downstream);
    }

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

            downstream.onSubscribe(this);
        }
    }

    @Override
    public void onError(Throwable t) {
        value = null;
        error(t);
    }

    @Override
    public void onComplete() {
        R v = value;
        if (v != null) {
            value = null;
            complete(v);
        } else {
            complete();
        }
    }

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