/*
    * Copyright 2022 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.netty5.handler.codec;
  
  import io.netty5.buffer.api.Buffer;
  import io.netty5.channel.ChannelHandler;
  import io.netty5.channel.ChannelHandlerAdapter;
  import io.netty5.channel.ChannelHandlerContext;
  import io.netty5.channel.ChannelPipeline;
  import io.netty5.util.concurrent.Future;
  import io.netty5.util.internal.TypeParameterMatcher;
  
  import static io.netty5.util.internal.SilentDispose.autoClosing;
  import static java.util.Objects.requireNonNull;
  
  /**
   * {@link ChannelHandler} which encodes message in a stream-like fashion from one message to a {@link Buffer}.
   *
   * <p>Example implementation which encodes {@link Integer}s to a {@link Buffer}.
   *
   * <pre>
   *     public class IntegerEncoder extends {@link MessageToByteEncoder}&lt;{@link Integer}&gt; {
   *         {@code @Override}
   *         public void encode({@link ChannelHandlerContext} ctx, {@link Integer} msg, {@link Buffer} out)
   *                 throws {@link Exception} {
   *             out.writeInt(msg);
   *         }
   *     }
   * </pre>
   */
  public abstract class MessageToByteEncoder<I> extends ChannelHandlerAdapter {
  
      private final TypeParameterMatcher matcher;
  
      /**
       * Create a new instance which will try to detect the types to match out of the type parameter of the class.
       */
      protected MessageToByteEncoder() {
          matcher = TypeParameterMatcher.find(this, MessageToByteEncoder.class, "I");
      }
  
      /**
       * Create a new instance.
       *
       * @param outboundMessageType The type of messages to match.
       */
      protected MessageToByteEncoder(Class<? extends I> outboundMessageType) {
          matcher = TypeParameterMatcher.get(requireNonNull(outboundMessageType, "outboundMessageType"));
      }
  
      /**
       * Returns {@code true} if the given message should be handled. If {@code false} it will be passed to the next
       * {@link ChannelHandler} in the {@link ChannelPipeline}.
       */
      public boolean acceptOutboundMessage(Object msg) throws Exception {
          return matcher.match(msg);
      }
  
      @Override
      public Future<Void> write(ChannelHandlerContext ctx, Object msg) {
          Buffer buf = null;
          try {
              if (acceptOutboundMessage(msg)) {
                  @SuppressWarnings("unchecked")
                  I cast = (I) msg;
                  buf = allocateBuffer(ctx, cast);
                  try (AutoCloseable ignore = autoClosing(cast)) {
                      encode(ctx, cast, buf);
                  }
  
                  if (buf.readableBytes() > 0) {
                      Future<Void> f = ctx.write(buf);
                      buf = null;
                      return f;
                  }
                  return ctx.write(ctx.bufferAllocator().allocate(0));
              }
              return ctx.write(msg);
          } catch (EncoderException e) {
              return ctx.newFailedFuture(e);
          } catch (Throwable e) {
              return ctx.newFailedFuture(new EncoderException(e));
          } finally {
              if (buf != null) {
                  buf.close();
              }
         }
     }
 
     /**
      * Allocate a {@link Buffer} which will be used as argument of {@link #encode(ChannelHandlerContext, I, Buffer)}.
      *
      * @param ctx the {@link ChannelHandlerContext} which this {@link MessageToByteEncoder} belongs to
      * @param msg the message to be encoded
      */
     protected abstract Buffer allocateBuffer(ChannelHandlerContext ctx, I msg) throws Exception;
 
     /**
      * Encode a message into a {@link Buffer}. This method will be called for each written message that can be handled
      * by this encoder.
      *
      * @param ctx the {@link ChannelHandlerContext} which this {@link MessageToByteEncoder} belongs to
      * @param msg the message to encode
      * @param out the {@link Buffer} into which the encoded message will be written
      * @throws Exception is thrown if an error occurs
      */
     protected abstract void encode(ChannelHandlerContext ctx, I msg, Buffer out) throws Exception;
 }