/**
    * 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.hadoop.hbase.ipc;
  
  import io.netty.channel.ChannelDuplexHandler;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  
  import java.io.IOException;
  import java.util.HashMap;
  import java.util.Map;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  
  /**
   * We will expose the connection to upper layer before initialized, so we need to buffer the calls
   * passed in and write them out once the connection is established.
   */
  @InterfaceAudience.Private
  class BufferCallBeforeInitHandler extends ChannelDuplexHandler {
  
    private enum BufferCallAction {
      FLUSH, FAIL
    }
  
    public static final class BufferCallEvent {
  
      public final BufferCallAction action;
  
      public final IOException error;
  
      private BufferCallEvent(BufferCallBeforeInitHandler.BufferCallAction action,
          IOException error) {
        this.action = action;
        this.error = error;
      }
  
      public static BufferCallBeforeInitHandler.BufferCallEvent success() {
        return SUCCESS_EVENT;
      }
  
      public static BufferCallBeforeInitHandler.BufferCallEvent fail(IOException error) {
        return new BufferCallEvent(BufferCallAction.FAIL, error);
      }
    }
  
    private static final BufferCallEvent SUCCESS_EVENT = new BufferCallEvent(BufferCallAction.FLUSH,
        null);
  
    private final Map<Integer, Call> id2Call = new HashMap<>();
  
    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) {
      if (msg instanceof Call) {
        Call call = (Call) msg;
        id2Call.put(call.id, call);
        // The call is already in track so here we set the write operation as success.
        // We will fail the call directly if we can not write it out.
        promise.trySuccess();
      } else {
        ctx.write(msg, promise);
      }
    }
  
    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
      if (evt instanceof BufferCallEvent) {
        BufferCallEvent bcEvt = (BufferCallBeforeInitHandler.BufferCallEvent) evt;
        switch (bcEvt.action) {
          case FLUSH:
            for (Call call : id2Call.values()) {
              ctx.write(call);
            }
            break;
          case FAIL:
            for (Call call : id2Call.values()) {
              call.setException(bcEvt.error);
            }
            break;
        }
        ctx.flush();
        ctx.pipeline().remove(this);
      } else if (evt instanceof CallEvent) {
        // just remove the call for now until we add other call event other than timeout and cancel.
       id2Call.remove(((CallEvent) evt).call.id);
     } else {
       ctx.fireUserEventTriggered(evt);
     }
   }
 }