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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.operators;

import rx.Observable;
import rx.Observable.OnSubscribeFunc;
import rx.Observer;
import rx.Subscription;
import rx.functions.Action0;

/**
 * Registers an action to be called when an Observable invokes onComplete or onError.
 * 
 * 
 * 

 * See also the MSDN
 * Observable.Finally method
 */
public final class OperationFinally {

    /**
     * Call a given action when a sequence completes (with or without an
     * exception). The returned observable is exactly as threadsafe as the
     * source observable.
     * 
     * Note that "finally" is a Java reserved word and cannot be an identifier,
     * so we use "finallyDo".
     * 
     * @param sequence
     *            An observable sequence of elements
     * @param action
     *            An action to be taken when the sequence is complete or throws an exception
     * @return An observable sequence with the same elements as the input.
     *         After the last element is consumed (and {@link Observer#onCompleted} has been called),
     *         or after an exception is thrown (and {@link Observer#onError} has been called),
     *         the given action will be called.
     * @see MSDN Observable.Finally method
     */
    public static  OnSubscribeFunc finallyDo(final Observable sequence, final Action0 action) {
        return new OnSubscribeFunc() {
            @Override
            public Subscription onSubscribe(Observer observer) {
                return new Finally(sequence, action).onSubscribe(observer);
            }
        };
    }

    private static class Finally implements OnSubscribeFunc {
        private final Observable sequence;
        private final Action0 finalAction;

        Finally(final Observable sequence, Action0 finalAction) {
            this.sequence = sequence;
            this.finalAction = finalAction;
        }

        public Subscription onSubscribe(Observer observer) {
            return sequence.subscribe(new FinallyObserver(observer));
        }

        private class FinallyObserver implements Observer {
            private final Observer observer;

            FinallyObserver(Observer observer) {
                this.observer = observer;
            }

            @Override
            public void onCompleted() {
                try {
                    observer.onCompleted();
                } finally {
                    finalAction.call();
                }
            }

            @Override
            public void onError(Throwable e) {
                try {
                    observer.onError(e);
                } finally {
                    finalAction.call();
                }
            }

            @Override
            public void onNext(T args) {
                observer.onNext(args);
            }
        }
    }
}