content: /*
   * Copyright 1999-2022 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
   *
   *      https://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.csp.sentinel.command.handler;
  
  import com.alibaba.csp.sentinel.command.*;
  import com.alibaba.csp.sentinel.util.AssertUtil;
  
  import java.util.Iterator;
  import java.util.List;
  import java.util.function.Function;
  
  /**
   * intercept specified command handler
   *
   * @author icodening
   * @date 2022.03.03
   */
  public class InterceptingCommandHandler<R> implements CommandHandler<R> {
  
      private final CommandHandler<R> delegate;
  
      private final List<CommandHandlerInterceptor<R>> commandHandlerInterceptors;
  
      public InterceptingCommandHandler(CommandHandler<R> delegate, List<CommandHandlerInterceptor<R>> commandHandlerInterceptors) {
          AssertUtil.notNull(delegate, "delegate cannot be null");
          AssertUtil.notNull(commandHandlerInterceptors, "commandHandlerInterceptors cannot be null");
          this.delegate = delegate;
          this.commandHandlerInterceptors = commandHandlerInterceptors;
      }
  
      @Override
      public CommandResponse<R> handle(CommandRequest request) {
          return new InterceptingRequestExecution<>(commandHandlerInterceptors.iterator(), delegate::handle).execute(request);
      }
  
      private static class InterceptingRequestExecution<R> implements CommandRequestExecution<R> {
  
          private final Iterator<CommandHandlerInterceptor<R>> iterator;
  
          private final Function<CommandRequest, CommandResponse<R>> commandResponseFunction;
  
          public InterceptingRequestExecution(Iterator<CommandHandlerInterceptor<R>> iterator,
                                              Function<CommandRequest, CommandResponse<R>> commandResponseFunction) {
              this.iterator = iterator;
              this.commandResponseFunction = commandResponseFunction;
          }
  
          @Override
          public CommandResponse<R> execute(CommandRequest request) {
              if (this.iterator.hasNext()) {
                  CommandHandlerInterceptor<R> nextInterceptor = this.iterator.next();
                  return nextInterceptor.intercept(request, this);
              }
              return commandResponseFunction.apply(request);
          }
      }
  }
  