content: /*
   * Copyright 1999-2023 Alibaba Group Holding Ltd.
   *
   * 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 com.alibaba.nacos.client.selector;
  
  import com.alibaba.nacos.api.selector.client.Selector;
  import com.alibaba.nacos.common.notify.Event;
  
  import java.util.Objects;
  
  /**
   * Selector Wrapper.
   *
   * @param <S> the type of selector
   * @param <T> the type of original event
   * @param <E> the type of listener callback event
   * @author lideyou
   */
  public abstract class AbstractSelectorWrapper<S extends Selector<?, ?>, E, T extends Event> {
      
      private final S selector;
      
      private final ListenerInvoker<E> listener;
      
      public AbstractSelectorWrapper(S selector, ListenerInvoker<E> listener) {
          this.selector = selector;
          this.listener = listener;
      }
      
      /**
       * Check whether the event can be callback.
       *
       * @param event original event
       * @return true if the event can be callback
       */
      protected abstract boolean isSelectable(T event);
      
      /**
       * Check whether the result can be callback.
       *
       * @param event select result
       * @return true if the result can be callback
       */
      protected abstract boolean isCallable(E event);
      
      /**
       * Build an event received by the listener.
       *
       * @param event original event
       * @return listener event
       */
      protected abstract E buildListenerEvent(T event);
      
      /**
       * Notify listener.
       *
       * @param event original event
       */
      public void notifyListener(T event) {
          if (!isSelectable(event)) {
              return;
          }
          E newEvent = buildListenerEvent(event);
          if (isCallable(newEvent)) {
              // lock listener to make sure isInvoked is thread safe.
              synchronized (listener) {
                  listener.invoke(newEvent);
              }
          }
      }
      
      /**
       * Notify listener If the listener is not invoked.
       *
       * @param event original event
       */
      public void notifyIfListenerIfNotNotified(T event) {
          if (!isSelectable(event)) {
              return;
          }
          E newEvent = buildListenerEvent(event);
          synchronized (listener) {
              if (!listener.isInvoked()) {
                  listener.invoke(newEvent);
              }
          }
      }
      
      public ListenerInvoker<E> getListener() {
          return this.listener;
      }
      
      public S getSelector() {
          return this.selector;
      }
      
      @Override
      public boolean equals(Object o) {
          if (this == o) {
              return true;
          }
          if (o == null || getClass() != o.getClass()) {
              return false;
          }
          AbstractSelectorWrapper<?, ?, ?> that = (AbstractSelectorWrapper<?, ?, ?>) o;
          return Objects.equals(selector, that.selector) && Objects.equals(listener, that.listener);
      }
      
      @Override
      public int hashCode() {
          return Objects.hash(selector, listener);
      }
  }
  