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   /*
    * Copyright 2016 The Netty Project
    *
    * The Netty Project 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:
    *
    * 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 io.netty.handler.codec.redis;
  
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.CodecException;
  import io.netty.handler.codec.MessageToMessageDecoder;
  import io.netty.util.ReferenceCountUtil;
  import io.netty.util.internal.UnstableApi;
  
  import java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.Deque;
  import java.util.List;
  
  /**
   * Aggregates {@link RedisMessage} parts into {@link ArrayRedisMessage}. This decoder
   * should be used together with {@link RedisDecoder}.
   */
  @UnstableApi
  public final class RedisArrayAggregator extends MessageToMessageDecoder<RedisMessage> {
  
      private final Deque<AggregateState> depths = new ArrayDeque<AggregateState>(4);
  
      @Override
      protected void decode(ChannelHandlerContext ctx, RedisMessage msg, List<Object> out) throws Exception {
          if (msg instanceof ArrayHeaderRedisMessage) {
              msg = decodeRedisArrayHeader((ArrayHeaderRedisMessage) msg);
              if (msg == null) {
                  return;
              }
          } else {
              ReferenceCountUtil.retain(msg);
          }
  
          while (!depths.isEmpty()) {
              AggregateState current = depths.peek();
              current.children.add(msg);
  
              // if current aggregation completed, go to parent aggregation.
              if (current.children.size() == current.length) {
                  msg = new ArrayRedisMessage(current.children);
                  depths.pop();
              } else {
                  // not aggregated yet. try next time.
                  return;
              }
          }
  
          out.add(msg);
      }
  
      private RedisMessage decodeRedisArrayHeader(ArrayHeaderRedisMessage header) {
          if (header.isNull()) {
              return ArrayRedisMessage.NULL_INSTANCE;
          } else if (header.length() == 0L) {
              return ArrayRedisMessage.EMPTY_INSTANCE;
          } else if (header.length() > 0L) {
              // Currently, this codec doesn't support `long` length for arrays because Java's List.size() is int.
              if (header.length() > Integer.MAX_VALUE) {
                  throw new CodecException("this codec doesn't support longer length than " + Integer.MAX_VALUE);
              }
  
              // start aggregating array
              depths.push(new AggregateState((int) header.length()));
              return null;
          } else {
              throw new CodecException("bad length: " + header.length());
          }
      }
  
      private static final class AggregateState {
          private final int length;
          private final List<RedisMessage> children;
          AggregateState(int length) {
              this.length = length;
              this.children = new ArrayList<RedisMessage>(length);
          }
      }
  }