/*
    * Copyright 2015 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.socksx;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPipeline;
  import io.netty.handler.codec.ByteToMessageDecoder;
  import io.netty.handler.codec.socksx.v4.Socks4ServerDecoder;
  import io.netty.handler.codec.socksx.v4.Socks4ServerEncoder;
  import io.netty.handler.codec.socksx.v5.Socks5AddressEncoder;
  import io.netty.handler.codec.socksx.v5.Socks5InitialRequestDecoder;
  import io.netty.handler.codec.socksx.v5.Socks5ServerEncoder;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.util.List;
  
  /**
   * Detects the version of the current SOCKS connection and initializes the pipeline with
   * {@link Socks4ServerDecoder} or {@link Socks5InitialRequestDecoder}.
   */
  public class SocksPortUnificationServerHandler extends ByteToMessageDecoder {
  
      private static final InternalLogger logger =
              InternalLoggerFactory.getInstance(SocksPortUnificationServerHandler.class);
  
      private final Socks5ServerEncoder socks5encoder;
  
      /**
       * Creates a new instance with the default configuration.
       */
      public SocksPortUnificationServerHandler() {
          this(Socks5ServerEncoder.DEFAULT);
      }
  
      /**
       * Creates a new instance with the specified {@link Socks5ServerEncoder}.
       * This constructor is useful when a user wants to use an alternative {@link Socks5AddressEncoder}.
       */
      public SocksPortUnificationServerHandler(Socks5ServerEncoder socks5encoder) {
          this.socks5encoder = ObjectUtil.checkNotNull(socks5encoder, "socks5encoder");
      }
  
      @Override
      protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
          final int readerIndex = in.readerIndex();
          if (in.writerIndex() == readerIndex) {
              return;
          }
  
          ChannelPipeline p = ctx.pipeline();
          final byte versionVal = in.getByte(readerIndex);
          SocksVersion version = SocksVersion.valueOf(versionVal);
  
          switch (version) {
          case SOCKS4a:
              logKnownVersion(ctx, version);
              p.addAfter(ctx.name(), null, Socks4ServerEncoder.INSTANCE);
              p.addAfter(ctx.name(), null, new Socks4ServerDecoder());
              break;
          case SOCKS5:
              logKnownVersion(ctx, version);
              p.addAfter(ctx.name(), null, socks5encoder);
              p.addAfter(ctx.name(), null, new Socks5InitialRequestDecoder());
              break;
          default:
              logUnknownVersion(ctx, versionVal);
              in.skipBytes(in.readableBytes());
              ctx.close();
              return;
          }
  
          p.remove(this);
      }
  
      private static void logKnownVersion(ChannelHandlerContext ctx, SocksVersion version) {
          logger.debug("{} Protocol version: {}({})", ctx.channel(), version);
      }
  
      private static void logUnknownVersion(ChannelHandlerContext ctx, byte versionVal) {
          if (logger.isDebugEnabled()) {
              logger.debug("{} Unknown protocol version: {}", ctx.channel(), versionVal & 0xFF);
          }
     }
 }