/*
    * Copyright 2014 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.stomp;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.MessageToMessageEncoder;
  
  import java.util.List;
  import java.util.Map.Entry;
  
  import static io.netty.handler.codec.stomp.StompConstants.*;
  
  /**
   * Encodes a {@link StompFrame} or a {@link StompSubframe} into a {@link ByteBuf}.
   */
  public class StompSubframeEncoder extends MessageToMessageEncoder<StompSubframe> {
  
      @Override
      protected void encode(ChannelHandlerContext ctx, StompSubframe msg, List<Object> out) throws Exception {
          if (msg instanceof StompFrame) {
              StompFrame stompFrame = (StompFrame) msg;
              ByteBuf buf = encodeFullFrame(stompFrame, ctx);
  
              out.add(convertFullFrame(stompFrame, buf));
          } else if (msg instanceof StompHeadersSubframe) {
              StompHeadersSubframe stompHeadersSubframe = (StompHeadersSubframe) msg;
              ByteBuf buf = ctx.alloc().buffer(headersSubFrameSize(stompHeadersSubframe));
              encodeHeaders(stompHeadersSubframe, buf);
  
              out.add(convertHeadersSubFrame(stompHeadersSubframe, buf));
          } else if (msg instanceof StompContentSubframe) {
              StompContentSubframe stompContentSubframe = (StompContentSubframe) msg;
              ByteBuf buf = encodeContent(stompContentSubframe, ctx);
  
              out.add(convertContentSubFrame(stompContentSubframe, buf));
          }
      }
  
      /**
       * An extension method to convert a STOMP encoded buffer to a different message type
       * based on an original {@link StompFrame} full frame.
       *
       * <p>By default an encoded buffer is returned as is.
       */
      protected Object convertFullFrame(StompFrame original, ByteBuf encoded) {
          return encoded;
      }
  
      /**
       * An extension method to convert a STOMP encoded buffer to a different message type
       * based on an original {@link StompHeadersSubframe} headers sub frame.
       *
       * <p>By default an encoded buffer is returned as is.
       */
      protected Object convertHeadersSubFrame(StompHeadersSubframe original, ByteBuf encoded) {
          return encoded;
      }
  
      /**
       * An extension method to convert a STOMP encoded buffer to a different message type
       * based on an original {@link StompHeadersSubframe} content sub frame.
       *
       * <p>By default an encoded buffer is returned as is.
       */
      protected Object convertContentSubFrame(StompContentSubframe original, ByteBuf encoded) {
          return encoded;
      }
  
      /**
       * Returns a heuristic size for headers (32 bytes per header line) + (2 bytes for colon and eol) + (additional
       * command buffer).
       */
      protected int headersSubFrameSize(StompHeadersSubframe headersSubframe) {
          int estimatedSize = headersSubframe.headers().size() * 34 + 48;
          if (estimatedSize < 128) {
              return 128;
          } else if (estimatedSize < 256) {
              return 256;
          }
  
          return estimatedSize;
      }
  
      private ByteBuf encodeFullFrame(StompFrame frame, ChannelHandlerContext ctx) {
         int contentReadableBytes = frame.content().readableBytes();
         ByteBuf buf = ctx.alloc().buffer(headersSubFrameSize(frame) + contentReadableBytes);
         encodeHeaders(frame, buf);
 
         if (contentReadableBytes > 0) {
             buf.writeBytes(frame.content());
         }
 
         return buf.writeByte(NUL);
     }
 
     private static void encodeHeaders(StompHeadersSubframe frame, ByteBuf buf) {
         ByteBufUtil.writeUtf8(buf, frame.command().toString());
         buf.writeByte(StompConstants.LF);
 
         for (Entry<CharSequence, CharSequence> entry : frame.headers()) {
             ByteBufUtil.writeUtf8(buf, entry.getKey());
             buf.writeByte(StompConstants.COLON);
             ByteBufUtil.writeUtf8(buf, entry.getValue());
             buf.writeByte(StompConstants.LF);
         }
 
         buf.writeByte(StompConstants.LF);
     }
 
     private static ByteBuf encodeContent(StompContentSubframe content, ChannelHandlerContext ctx) {
         if (content instanceof LastStompContentSubframe) {
             ByteBuf buf = ctx.alloc().buffer(content.content().readableBytes() + 1);
             buf.writeBytes(content.content());
             buf.writeByte(StompConstants.NUL);
             return buf;
         }
 
         return content.content().retain();
     }
 }