/**
 * 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.subscriptions;

import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;

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

/**
 * Subscription that can be checked for status such as in a loop inside an {@link Observable} to exit the loop
 * if unsubscribed.
 * 
 * @see <a href="http://msdn.microsoft.com/en-us/library/system.reactive.disposables.booleandisposable(v=vs.103).aspx">Rx.Net equivalent BooleanDisposable</a>
 */
public final class BooleanSubscription implements Subscription {

    private final Action0 action;
    volatile int unsubscribed;
    static final AtomicIntegerFieldUpdater<BooleanSubscription> UNSUBSCRIBED_UPDATER
            = AtomicIntegerFieldUpdater.newUpdater(BooleanSubscription.class, "unsubscribed");

    public BooleanSubscription() {
        action = null;
    }

    private BooleanSubscription(Action0 action) {
        this.action = action;
    }

    /**
     * Creates a {@code BooleanSubscription} without unsubscribe behavior.
     *
     * @return the created {@code BooleanSubscription}
     */
    public static BooleanSubscription create() {
        return new BooleanSubscription();
    }

    /**
     * Creates a {@code BooleanSubscription} with a specified function to invoke upon unsubscribe.
     *
     * @param onUnsubscribe
     *          an {@link Action0} to invoke upon unsubscribe
     * @return the created {@code BooleanSubscription}
     */
    public static BooleanSubscription create(Action0 onUnsubscribe) {
        return new BooleanSubscription(onUnsubscribe);
    }

    @Override
    public boolean isUnsubscribed() {
        return unsubscribed != 0;
    }

    @Override
    public final void unsubscribe() {
        if (UNSUBSCRIBED_UPDATER.compareAndSet(this, 0, 1)) {
            if (action != null) {
                action.call();
            }
        }
    }

}