/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.dubbo.registry;

import org.apache.dubbo.common.URL;
import org.apache.dubbo.registry.client.event.listener.ServiceInstancesChangedListener;

import java.util.List;

/**
 * NotifyListener. (API, Prototype, ThreadSafe)
 *
 * @see org.apache.dubbo.registry.RegistryService#subscribe(URL, NotifyListener)
 */
public interface NotifyListener {

    /**
     * Triggered when a service change notification is received.
     * <p>
     * Notify needs to support the contract: <br>
     * 1. Always notifications on the service interface and the dimension of the data type. that is, won't notify part of the same type data belonging to one service. Users do not need to compare the results of the previous notification.<br>
     * 2. The first notification at a subscription must be a full notification of all types of data of a service.<br>
     * 3. At the time of change, different types of data are allowed to be notified separately, e.g.: providers, consumers, routers, overrides. It allows only one of these types to be notified, but the data of this type must be full, not incremental.<br>
     * 4. If a data type is empty, need to notify a empty protocol with category parameter identification of url data.<br>
     * 5. The order of notifications to be guaranteed by the notifications(That is, the implementation of the registry). Such as: single thread push, queue serialization, and version comparison.<br>
     *
     * @param urls The list of registered information , is always not empty. The meaning is the same as the return value of {@link org.apache.dubbo.registry.RegistryService#lookup(URL)}.
     */
    void notify(List<URL> urls);

    default void addServiceListener(ServiceInstancesChangedListener instanceListener) {}

    default ServiceInstancesChangedListener getServiceListener() {
        return null;
    }

    default URL getConsumerUrl() {
        return null;
    }
}
