/*
 * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.controller.md.sal.dom.api;

import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import java.util.concurrent.TimeUnit;
import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import org.opendaylight.controller.sal.core.api.BrokerService;

/**
 * A {@link DOMService} which allows its user to send {@link DOMNotification}s. It
 * provides two styles of initiating the notification delivery, similar to
 * {@link java.util.concurrent.BlockingQueue}:
 * - a put-style method which waits until the implementation can accept the notification
 *   for delivery, and
 * - an offer-style method, which attempts to enqueue the notification, but allows
 *   the caller to specify that it should never wait, or put an upper bound on how
 *   long it is going to wait.
 */
public interface DOMNotificationPublishService extends DOMService, BrokerService {
    /**
     * Well-known value indicating that the implementation is currently not
     * able to accept a notification.
     */
    ListenableFuture<Object> REJECTED = Futures.immediateFailedFuture(new DOMNotificationRejectedException("Unacceptable blocking conditions encountered"));

    /**
     * Publish a notification. The result of this method is a {@link ListenableFuture}
     * which will complete once the notification has been delivered to all immediate
     * registrants. The type of the object resulting from the future is not defined
     * and implementations may use it to convey additional information related to the
     * publishing process.
     *
     * Abstract subclasses can refine the return type as returning a promise of a
     * more specific type, e.g.:
     *
     *     public interface DeliveryStatus { int getListenerCount(); }
     *     ListenableFuture<? extends DeliveryStatus> putNotification(DOMNotification notification);
     *
     * Once the Future succeeds, the resulting object can be queried for traits using
     * instanceof, e.g:
     *
     *     // Can block when (for example) the implemention's ThreadPool queue is full
     *     Object o = service.putNotification(notif).get();
     *     if (o instanceof DeliveryStatus) {
     *         DeliveryStatus ds = (DeliveryStatus)o;
     *         LOG.debug("Notification was received by {} listeners", ds.getListenerCount(););
     *     }
     * }
     *
     * In case an implementation is running out of resources, it can block the calling
     * thread until enough resources become available to accept the notification for
     * processing, or it is interrupted.
     *
     * Caution: completion here means that the implementation has completed processing
     *          of the notification. This does not mean that all existing registrants
     *          have seen the notification. Most importantly, the delivery process at
     *          other cluster nodes may have not begun yet.
     *
     * @param notification Notification to be published.
     * @return A listenable future which will report completion when the service
     *         has finished propagating the notification to its immediate registrants.
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if notification is null.
     */
    @Nonnull ListenableFuture<?> putNotification(@Nonnull DOMNotification notification) throws InterruptedException;

    /**
     * Attempt to publish a notification. The result of this method is a {@link ListenableFuture}
     * which will complete once the notification has been delivered to all immediate
     * registrants. The type of the object resulting from the future is not defined
     * and implementations may use it to convey additional information related to the
     * publishing process. Unlike {@link #putNotification(DOMNotification)}, this method
     * is guaranteed not to block if the underlying implementation encounters contention.
     *
     * @param notification Notification to be published.
     * @return A listenable future which will report completion when the service
     *         has finished propagating the notification to its immediate registrants,
     *         or {@value #REJECTED} if resource constraints prevent
     *         the implementation from accepting the notification for delivery.
     * @throws NullPointerException if notification is null.
     */
    @Nonnull ListenableFuture<?> offerNotification(@Nonnull DOMNotification notification);

    /**
     * Attempt to publish a notification. The result of this method is a {@link ListenableFuture}
     * which will complete once the notification has been delivered to all immediate
     * registrants. The type of the object resulting from the future is not defined
     * and implementations may use it to convey additional information related to the
     * publishing process. Unlike {@link #putNotification(DOMNotification)}, this method
     * is guaranteed to block more than the specified timeout.
     *
     * @param notification Notification to be published.
     * @param timeout how long to wait before giving up, in units of unit
     * @param unit a TimeUnit determining how to interpret the timeout parameter
     * @return A listenable future which will report completion when the service
     *         has finished propagating the notification to its immediate registrants,
     *         or {@value #REJECTED} if resource constraints prevent
     *         the implementation from accepting the notification for delivery.
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if notification or unit is null.
     * @throws IllegalArgumentException if timeout is negative.
     */
    @Nonnull ListenableFuture<?> offerNotification(@Nonnull DOMNotification notification,
        @Nonnegative long timeout, @Nonnull TimeUnit unit) throws InterruptedException;
}