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/**
 * Copyright 2014 Netflix, Inc.
 * 
 * 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 rx.internal.operators;

import java.util.ArrayDeque;
import java.util.Deque;

import rx.Observable.Operator;
import rx.Subscriber;

/**
 * Returns an Observable that emits the at most the last count items emitted by the source Observable.
 * 

 * 
 */
public final class OperatorTakeLast implements Operator {

    private final int count;

    public OperatorTakeLast(int count) {
        if (count < 0) {
            throw new IndexOutOfBoundsException("count cannot be negative");
        }
        this.count = count;
    }

    @Override
    public Subscriber call(final Subscriber subscriber) {
        final Deque deque = new ArrayDeque();
        final NotificationLite notification = NotificationLite.instance();
        final TakeLastQueueProducer producer = new TakeLastQueueProducer(notification, deque, subscriber);
        subscriber.setProducer(producer);

        return new Subscriber(subscriber) {

            // no backpressure up as it wants to receive and discard all but the last
            @Override
            public void onStart() {
                // we do this to break the chain of the child subscriber being passed through
                request(Long.MAX_VALUE);
            }

            @Override
            public void onCompleted() {
                deque.offer(notification.completed());
                producer.startEmitting();
            }

            @Override
            public void onError(Throwable e) {
                deque.clear();
                subscriber.onError(e);
            }

            @Override
            public void onNext(T value) {
                if (count == 0) {
                    // If count == 0, we do not need to put value into deque and
                    // remove it at once. We can ignore the value directly.
                    return;
                }
                if (deque.size() == count) {
                    deque.removeFirst();
                }
                deque.offerLast(notification.next(value));
            }
        };
    }
}
 















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