/*
    * Copyright 2012 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.http;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.FileRegion;
  import io.netty.handler.codec.MessageToMessageEncoder;
  import io.netty.util.CharsetUtil;
  import io.netty.util.internal.StringUtil;
  
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map.Entry;
  
  import static io.netty.buffer.Unpooled.directBuffer;
  import static io.netty.buffer.Unpooled.unreleasableBuffer;
  import static io.netty.handler.codec.http.HttpConstants.CR;
  import static io.netty.handler.codec.http.HttpConstants.LF;
  
  /**
   * Encodes an {@link HttpMessage} or an {@link HttpContent} into
   * a {@link ByteBuf}.
   *
   * <h3>Extensibility</h3>
   *
   * Please note that this encoder is designed to be extended to implement
   * a protocol derived from HTTP, such as
   * <a href="https://en.wikipedia.org/wiki/Real_Time_Streaming_Protocol">RTSP</a> and
   * <a href="https://en.wikipedia.org/wiki/Internet_Content_Adaptation_Protocol">ICAP</a>.
   * To implement the encoder of such a derived protocol, extend this class and
   * implement all abstract methods properly.
   */
  public abstract class HttpObjectEncoder<H extends HttpMessage> extends MessageToMessageEncoder<Object> {
      static final int CRLF_SHORT = (CR << 8) | LF;
      private static final int ZERO_CRLF_MEDIUM = ('0' << 16) | CRLF_SHORT;
      private static final byte[] ZERO_CRLF_CRLF = { '0', CR, LF, CR, LF };
      private static final ByteBuf CRLF_BUF = unreleasableBuffer(
              directBuffer(2).writeByte(CR).writeByte(LF)).asReadOnly();
      private static final ByteBuf ZERO_CRLF_CRLF_BUF = unreleasableBuffer(
              directBuffer(ZERO_CRLF_CRLF.length).writeBytes(ZERO_CRLF_CRLF)).asReadOnly();
      private static final float HEADERS_WEIGHT_NEW = 1 / 5f;
      private static final float HEADERS_WEIGHT_HISTORICAL = 1 - HEADERS_WEIGHT_NEW;
      private static final float TRAILERS_WEIGHT_NEW = HEADERS_WEIGHT_NEW;
      private static final float TRAILERS_WEIGHT_HISTORICAL = HEADERS_WEIGHT_HISTORICAL;
  
      private static final int ST_INIT = 0;
      private static final int ST_CONTENT_NON_CHUNK = 1;
      private static final int ST_CONTENT_CHUNK = 2;
      private static final int ST_CONTENT_ALWAYS_EMPTY = 3;
  
      @SuppressWarnings("RedundantFieldInitialization")
      private int state = ST_INIT;
  
      /**
       * Used to calculate an exponential moving average of the encoded size of the initial line and the headers for
       * a guess for future buffer allocations.
       */
      private float headersEncodedSizeAccumulator = 256;
  
      /**
       * Used to calculate an exponential moving average of the encoded size of the trailers for
       * a guess for future buffer allocations.
       */
      private float trailersEncodedSizeAccumulator = 256;
  
      @Override
      protected void encode(ChannelHandlerContext ctx, Object msg, List<Object> out) throws Exception {
          ByteBuf buf = null;
          if (msg instanceof HttpMessage) {
              if (state != ST_INIT) {
                  throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg)
                          + ", state: " + state);
              }
  
              @SuppressWarnings({ "unchecked", "CastConflictsWithInstanceof" })
              H m = (H) msg;
  
              buf = ctx.alloc().buffer((int) headersEncodedSizeAccumulator);
              // Encode the message.
              encodeInitialLine(buf, m);
              state = isContentAlwaysEmpty(m) ? ST_CONTENT_ALWAYS_EMPTY :
                      HttpUtil.isTransferEncodingChunked(m) ? ST_CONTENT_CHUNK : ST_CONTENT_NON_CHUNK;
  
             sanitizeHeadersBeforeEncode(m, state == ST_CONTENT_ALWAYS_EMPTY);
 
             encodeHeaders(m.headers(), buf);
             ByteBufUtil.writeShortBE(buf, CRLF_SHORT);
 
             headersEncodedSizeAccumulator = HEADERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) +
                                             HEADERS_WEIGHT_HISTORICAL * headersEncodedSizeAccumulator;
         }
 
         // Bypass the encoder in case of an empty buffer, so that the following idiom works:
         //
         //     ch.write(Unpooled.EMPTY_BUFFER).addListener(ChannelFutureListener.CLOSE);
         //
         // See https://github.com/netty/netty/issues/2983 for more information.
         if (msg instanceof ByteBuf) {
             final ByteBuf potentialEmptyBuf = (ByteBuf) msg;
             if (!potentialEmptyBuf.isReadable()) {
                 out.add(potentialEmptyBuf.retain());
                 return;
             }
         }
 
         if (msg instanceof HttpContent || msg instanceof ByteBuf || msg instanceof FileRegion) {
             switch (state) {
                 case ST_INIT:
                     throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg)
                         + ", state: " + state);
                 case ST_CONTENT_NON_CHUNK:
                     final long contentLength = contentLength(msg);
                     if (contentLength > 0) {
                         if (buf != null && buf.writableBytes() >= contentLength && msg instanceof HttpContent) {
                             // merge into other buffer for performance reasons
                             buf.writeBytes(((HttpContent) msg).content());
                             out.add(buf);
                         } else {
                             if (buf != null) {
                                 out.add(buf);
                             }
                             out.add(encodeAndRetain(msg));
                         }
 
                         if (msg instanceof LastHttpContent) {
                             state = ST_INIT;
                         }
 
                         break;
                     }
 
                     // fall-through!
                 case ST_CONTENT_ALWAYS_EMPTY:
 
                     if (buf != null) {
                         // We allocated a buffer so add it now.
                         out.add(buf);
                     } else {
                         // Need to produce some output otherwise an
                         // IllegalStateException will be thrown as we did not write anything
                         // Its ok to just write an EMPTY_BUFFER as if there are reference count issues these will be
                         // propagated as the caller of the encode(...) method will release the original
                         // buffer.
                         // Writing an empty buffer will not actually write anything on the wire, so if there is a user
                         // error with msg it will not be visible externally
                         out.add(Unpooled.EMPTY_BUFFER);
                     }
 
                     break;
                 case ST_CONTENT_CHUNK:
                     if (buf != null) {
                         // We allocated a buffer so add it now.
                         out.add(buf);
                     }
                     encodeChunkedContent(ctx, msg, contentLength(msg), out);
 
                     break;
                 default:
                     throw new Error();
             }
 
             if (msg instanceof LastHttpContent) {
                 state = ST_INIT;
             }
         } else if (buf != null) {
             out.add(buf);
         }
     }
 
     /**
      * Encode the {@link HttpHeaders} into a {@link ByteBuf}.
      */
     protected void encodeHeaders(HttpHeaders headers, ByteBuf buf) {
         Iterator<Entry<CharSequence, CharSequence>> iter = headers.iteratorCharSequence();
         while (iter.hasNext()) {
             Entry<CharSequence, CharSequence> header = iter.next();
             HttpHeadersEncoder.encoderHeader(header.getKey(), header.getValue(), buf);
         }
     }
 
     private void encodeChunkedContent(ChannelHandlerContext ctx, Object msg, long contentLength, List<Object> out) {
         if (contentLength > 0) {
             String lengthHex = Long.toHexString(contentLength);
             ByteBuf buf = ctx.alloc().buffer(lengthHex.length() + 2);
             buf.writeCharSequence(lengthHex, CharsetUtil.US_ASCII);
             ByteBufUtil.writeShortBE(buf, CRLF_SHORT);
             out.add(buf);
             out.add(encodeAndRetain(msg));
             out.add(CRLF_BUF.duplicate());
         }
 
         if (msg instanceof LastHttpContent) {
             HttpHeaders headers = ((LastHttpContent) msg).trailingHeaders();
             if (headers.isEmpty()) {
                 out.add(ZERO_CRLF_CRLF_BUF.duplicate());
             } else {
                 ByteBuf buf = ctx.alloc().buffer((int) trailersEncodedSizeAccumulator);
                 ByteBufUtil.writeMediumBE(buf, ZERO_CRLF_MEDIUM);
                 encodeHeaders(headers, buf);
                 ByteBufUtil.writeShortBE(buf, CRLF_SHORT);
                 trailersEncodedSizeAccumulator = TRAILERS_WEIGHT_NEW * padSizeForAccumulation(buf.readableBytes()) +
                                                  TRAILERS_WEIGHT_HISTORICAL * trailersEncodedSizeAccumulator;
                 out.add(buf);
             }
         } else if (contentLength == 0) {
             // Need to produce some output otherwise an
             // IllegalStateException will be thrown
             out.add(encodeAndRetain(msg));
         }
     }
 
     /**
      * Allows to sanitize headers of the message before encoding these.
      */
     protected void sanitizeHeadersBeforeEncode(@SuppressWarnings("unused") H msg, boolean isAlwaysEmpty) {
         // noop
     }
 
     /**
      * Determine whether a message has a content or not. Some message may have headers indicating
      * a content without having an actual content, e.g the response to an HEAD or CONNECT request.
      *
      * @param msg the message to test
      * @return {@code true} to signal the message has no content
      */
     protected boolean isContentAlwaysEmpty(@SuppressWarnings("unused") H msg) {
         return false;
     }
 
     @Override
     public boolean acceptOutboundMessage(Object msg) throws Exception {
         return msg instanceof HttpObject || msg instanceof ByteBuf || msg instanceof FileRegion;
     }
 
     private static Object encodeAndRetain(Object msg) {
         if (msg instanceof ByteBuf) {
             return ((ByteBuf) msg).retain();
         }
         if (msg instanceof HttpContent) {
             return ((HttpContent) msg).content().retain();
         }
         if (msg instanceof FileRegion) {
             return ((FileRegion) msg).retain();
         }
         throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
     }
 
     private static long contentLength(Object msg) {
         if (msg instanceof HttpContent) {
             return ((HttpContent) msg).content().readableBytes();
         }
         if (msg instanceof ByteBuf) {
             return ((ByteBuf) msg).readableBytes();
         }
         if (msg instanceof FileRegion) {
             return ((FileRegion) msg).count();
         }
         throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
     }
 
     /**
      * Add some additional overhead to the buffer. The rational is that it is better to slightly over allocate and waste
      * some memory, rather than under allocate and require a resize/copy.
      * @param readableBytes The readable bytes in the buffer.
      * @return The {@code readableBytes} with some additional padding.
      */
     private static int padSizeForAccumulation(int readableBytes) {
         return (readableBytes << 2) / 3;
     }
 
     @Deprecated
     protected static void encodeAscii(String s, ByteBuf buf) {
         buf.writeCharSequence(s, CharsetUtil.US_ASCII);
     }
 
     protected abstract void encodeInitialLine(ByteBuf buf, H message) throws Exception;
 }