/*
 * Copyright 2016 Open Networking Laboratory
 *
 * 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 org.onosproject.store.service;

import java.util.concurrent.CompletableFuture;

/**
 * Distributed version of java.util.concurrent.atomic.AtomicReference.
 * <p>
 * All methods of this interface return a {@link CompletableFuture future} immediately
 * after a successful invocation. The operation itself is executed asynchronous and
 * the returned future will be {@link CompletableFuture#complete completed} when the
 * operation finishes.
 *
 * @param <V> value type
 */
public interface AsyncAtomicValue<V> {

    /**
     * Atomically sets the value to the given updated value if the current value is equal to the expected value.
     * <p>
     * IMPORTANT: Equality is based on the equality of the serialized {code byte[]} representations.
     * <p>
     * @param expect  the expected value
     * @param update  the new value
     * @return CompletableFuture that will be completed with {@code true} if update was successful. Otherwise future
     * will be completed with a value of {@code false}
     */
    CompletableFuture<Boolean> compareAndSet(V expect, V update);

    /**
     * Gets the current value.
     * @return CompletableFuture that will be completed with the value
     */
    CompletableFuture<V> get();

    /**
     * Atomically sets to the given value and returns the old value.
     * @param value the new value
     * @return CompletableFuture that will be completed with the previous value
     */
    CompletableFuture<V> getAndSet(V value);

    /**
     * Sets to the given value.
     * @param value value to set
     * @return CompletableFuture that will be completed when the operation finishes
     */
    CompletableFuture<Void> set(V value);

    /**
     * Registers the specified listener to be notified whenever the atomic value is updated.
     * @param listener listener to notify about events
     * @return CompletableFuture that will be completed when the operation finishes
     */
    CompletableFuture<Void> addListener(AtomicValueEventListener<V> listener);

    /**
     * Unregisters the specified listener such that it will no longer
     * receive atomic value update notifications.
     * @param listener listener to unregister
     * @return CompletableFuture that will be completed when the operation finishes
     */
    CompletableFuture<Void> removeListener(AtomicValueEventListener<V> listener);
}