/**
 * 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.Subscriber;
import rx.Subscription;
import rx.functions.Action0;

/**
 * Registers an action to be called when an Observable invokes onComplete or onError.
 * <p>
 * <img width="640" src="https://github.com/Netflix/RxJava/wiki/images/rx-operators/finallyDo.png">
 * <p>
 * See also the <a href="http://msdn.microsoft.com/en-us/library/hh212133(v=vs.103).aspx">MSDN
 * Observable.Finally method</a>
 */
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.
     * <p/>
     * 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 <a href="http://msdn.microsoft.com/en-us/library/hh212133(v=vs.103).aspx">MSDN Observable.Finally method</a>
     */
    public static <T> OnSubscribeFunc<T> finallyDo(final Observable<? extends T> sequence, final Action0 action) {
        return new OnSubscribeFunc<T>() {
            @Override
            public Subscription onSubscribe(Observer<? super T> observer) {
                return new Finally<T>(sequence, action).onSubscribe(observer);
            }
        };
    }

    private static class Finally<T> implements OnSubscribeFunc<T> {
        private final Observable<? extends T> sequence;
        private final Action0 finalAction;

        Finally(final Observable<? extends T> sequence, Action0 finalAction) {
            this.sequence = sequence;
            this.finalAction = finalAction;
        }

        public Subscription onSubscribe(Observer<? super T> observer) {
            return sequence.unsafeSubscribe(new FinallyObserver(observer));
        }

        private class FinallyObserver extends Subscriber<T> {
            private final Observer<? super T> observer;

            FinallyObserver(Observer<? super T> 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);
            }
        }
    }
}
