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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.*;
import io.reactivex.plugins.RxJavaPlugins;

public final class ObservableTake extends AbstractObservableWithUpstream {
    final long limit;
    public ObservableTake(ObservableSource source, long limit) {
        super(source);
        this.limit = limit;
    }

    @Override
    protected void subscribeActual(Observer observer) {
        source.subscribe(new TakeObserver(observer, limit));
    }

    static final class TakeObserver implements Observer, Disposable {
        final Observer downstream;

        boolean done;

        Disposable upstream;

        long remaining;
        TakeObserver(Observer actual, long limit) {
            this.downstream = actual;
            this.remaining = limit;
        }

        @Override
        public void onSubscribe(Disposable d) {
            if (DisposableHelper.validate(this.upstream, d)) {
                upstream = d;
                if (remaining == 0) {
                    done = true;
                    d.dispose();
                    EmptyDisposable.complete(downstream);
                } else {
                    downstream.onSubscribe(this);
                }
            }
        }

        @Override
        public void onNext(T t) {
            if (!done && remaining-- > 0) {
                boolean stop = remaining == 0;
                downstream.onNext(t);
                if (stop) {
                    onComplete();
                }
            }
        }

        @Override
        public void onError(Throwable t) {
            if (done) {
                RxJavaPlugins.onError(t);
                return;
            }

            done = true;
            upstream.dispose();
            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            if (!done) {
                done = true;
                upstream.dispose();
                downstream.onComplete();
            }
        }

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

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