/*
    * 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:
    *
    *   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 io.netty.channel;
  
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.util.AttributeKey;
  import io.netty.util.AttributeMap;
  import io.netty.util.concurrent.EventExecutor;
  import io.netty.util.concurrent.FutureListener;
  
  import java.net.ConnectException;
  import java.net.SocketAddress;
  import java.nio.channels.Channels;
  
  /**
   * Enables a {@link ChannelHandler} to interact with its {@link ChannelPipeline}
   * and other handlers.  A handler can notify the next {@link ChannelHandler} in the {@link ChannelPipeline},
   * modify the {@link ChannelPipeline} it belongs to dynamically.
   *
   * <h3>Notify</h3>
   *
   * You can notify the closest handler in the
   * same {@link ChannelPipeline} by calling one of the various methods provided here.
   * Please refer to {@link ChannelPipeline} to understand how an event flows.
   *
   * <h3>Modifying a pipeline</h3>
   *
   * You can get the {@link ChannelPipeline} your handler belongs to by calling
   * {@link #pipeline()}.  A non-trivial application could insert, remove, or
   * replace handlers in the pipeline dynamically at runtime.
   *
   * <h3>Retrieving for later use</h3>
   *
   * You can keep the {@link ChannelHandlerContext} for later use, such as
   * triggering an event outside the handler methods, even from a different thread.
   * <pre>
   * public class MyHandler extends {@link ChannelDuplexHandler} {
   *
   *     <b>private {@link ChannelHandlerContext} ctx;</b>
   *
   *     public void beforeAdd({@link ChannelHandlerContext} ctx) {
   *         <b>this.ctx = ctx;</b>
   *     }
   *
   *     public void login(String username, password) {
   *         ctx.write(new LoginMessage(username, password));
   *     }
   *     ...
   * }
   * </pre>
   *
   * <h3>Storing stateful information</h3>
   *
   * {@link #attr(AttributeKey)} allow you to
   * store and access stateful information that is related with a handler and its
   * context.  Please refer to {@link ChannelHandler} to learn various recommended
   * ways to manage stateful information.
   *
   * <h3>A handler can have more than one context</h3>
   *
   * Please note that a {@link ChannelHandler} instance can be added to more than
   * one {@link ChannelPipeline}.  It means a single {@link ChannelHandler}
   * instance can have more than one {@link ChannelHandlerContext} and therefore
   * the single instance can be invoked with different
   * {@link ChannelHandlerContext}s if it is added to one or more
   * {@link ChannelPipeline}s more than once.
   * <p>
   * For example, the following handler will have as many independent {@link AttributeKey}s
   * as how many times it is added to pipelines, regardless if it is added to the
   * same pipeline multiple times or added to different pipelines multiple times:
   * <pre>
   * public class FactorialHandler extends {@link ChannelInboundHandlerAdapter}&lt{@link Integer}&gt {
   *
   *   private final {@link AttributeKey}&lt;{@link Integer}&gt; counter =
   *           new {@link AttributeKey}&lt;{@link Integer}&gt;("counter");
   *
   *   // This handler will receive a sequence of increasing integers starting
   *   // from 1.
   *   {@code @Override}
   *   public void channelRead({@link ChannelHandlerContext} ctx, Object msg) {
   *     Integer a = ctx.attr(counter).get();
   *
   *     if (a == null) {
   *       a = 1;
  *     }
  *
  *     attr.set(a * integer));
  *   }
  * }
  *
  * // Different context objects are given to "f1", "f2", "f3", and "f4" even if
  * // they refer to the same handler instance.  Because the FactorialHandler
  * // stores its state in a context object (as an (using an {@link AttributeKey}), the factorial is
  * // calculated correctly 4 times once the two pipelines (p1 and p2) are active.
  * FactorialHandler fh = new FactorialHandler();
  *
  * {@link ChannelPipeline} p1 = {@link Channels}.pipeline();
  * p1.addLast("f1", fh);
  * p1.addLast("f2", fh);
  *
  * {@link ChannelPipeline} p2 = {@link Channels}.pipeline();
  * p2.addLast("f3", fh);
  * p2.addLast("f4", fh);
  * </pre>
  *
  * <h3>Additional resources worth reading</h3>
  * <p>
  * Please refer to the {@link ChannelHandler}, and
  * {@link ChannelPipeline} to find out more about inbound and outbound operations,
  * what fundamental differences they have, how they flow in a  pipeline,  and how to handle
  * the operation in your application.
  */
 public interface ChannelHandlerContext
          extends AttributeMap {
 
     /**
      * Return the {@link Channel} which is bound to the {@link ChannelHandlerContext}.
      */
     Channel channel();
 
     /**
      * The {@link EventExecutor} that is used to dispatch the events. This can also be used to directly
      * submit tasks that get executed in the event loop. For more information please refer to the
      * {@link EventExecutor} javadoc.
      */
     EventExecutor executor();
 
     /**
      * The unique name of the {@link ChannelHandlerContext}.The name was used when then {@link ChannelHandler}
      * was added to the {@link ChannelPipeline}. This name can also be used to access the registered
      * {@link ChannelHandler} from the {@link ChannelPipeline}.
      */
     String name();
 
     /**
      * The {@link ChannelHandler} that is bound this {@link ChannelHandlerContext}.
      */
     ChannelHandler handler();
 
     /**
      * Return {@code true} if the {@link ChannelHandler} which belongs to this context was removed
      * from the {@link ChannelPipeline}. Note that this method is only meant to be called from with in the
      * {@link EventLoop}.
      */
     boolean isRemoved();
 
     /**
      * A {@link Channel} was registered to its {@link EventLoop}.
      *
      * This will result in having the  {@link ChannelInboundHandler#channelRegistered(ChannelHandlerContext)} method
      * called of the next  {@link ChannelInboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelHandlerContext fireChannelRegistered();
 
     /**
      * A {@link Channel} was unregistered from its {@link EventLoop}.
      *
      * This will result in having the  {@link ChannelInboundHandler#channelUnregistered(ChannelHandlerContext)} method
      * called of the next  {@link ChannelInboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelHandlerContext fireChannelUnregistered();
 
     /**
      * A {@link Channel} is active now, which means it is connected.
      *
      * This will result in having the  {@link ChannelInboundHandler#channelActive(ChannelHandlerContext)} method
      * called of the next  {@link ChannelInboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelHandlerContext fireChannelActive();
 
     /**
      * A {@link Channel} is inactive now, which means it is closed.
      *
      * This will result in having the  {@link ChannelInboundHandler#channelInactive(ChannelHandlerContext)} method
      * called of the next  {@link ChannelInboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelHandlerContext fireChannelInactive();
 
     /**
      * A {@link Channel} received an {@link Throwable} in one of its inbound operations.
      *
      * This will result in having the  {@link ChannelInboundHandler#exceptionCaught(ChannelHandlerContext, Throwable)}
      * method  called of the next  {@link ChannelInboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelHandlerContext fireExceptionCaught(Throwable cause);
 
     /**
      * A {@link Channel} received an user defined event.
      *
      * This will result in having the  {@link ChannelInboundHandler#userEventTriggered(ChannelHandlerContext, Object)}
      * method  called of the next  {@link ChannelInboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelHandlerContext fireUserEventTriggered(Object evt);
 
     /**
      * A {@link Channel} received a message.
      *
      * This will result in having the {@link ChannelInboundHandler#channelRead(ChannelHandlerContext, Object)}
      * method  called of the next {@link ChannelInboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelHandlerContext fireChannelRead(Object msg);
 
     /**
      * Triggers an {@link ChannelInboundHandler#channelReadComplete(ChannelHandlerContext)}
      * event to the next {@link ChannelInboundHandler} in the {@link ChannelPipeline}.
      */
     ChannelHandlerContext fireChannelReadComplete();
 
     /**
      * Triggers an {@link ChannelInboundHandler#channelWritabilityChanged(ChannelHandlerContext)}
      * event to the next {@link ChannelInboundHandler} in the {@link ChannelPipeline}.
      */
     ChannelHandlerContext fireChannelWritabilityChanged();
 
     /**
      * Request to bind to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation
      * completes, either because the operation was successful or because of an error.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#bind(ChannelHandlerContext, SocketAddress, ChannelPromise)} method
      * called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture bind(SocketAddress localAddress);
 
     /**
      * Request to connect to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation
      * completes, either because the operation was successful or because of an error.
      * <p>
      * If the connection fails because of a connection timeout, the {@link ChannelFuture} will get failed with
      * a {@link ConnectTimeoutException}. If it fails because of connection refused a {@link ConnectException}
      * will be used.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture connect(SocketAddress remoteAddress);
 
     /**
      * Request to connect to the given {@link SocketAddress} while bind to the localAddress and notify the
      * {@link ChannelFuture} once the operation completes, either because the operation was successful or because of
      * an error.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress);
 
     /**
      * Request to disconnect from the remote peer and notify the {@link ChannelFuture} once the operation completes,
      * either because the operation was successful or because of an error.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#disconnect(ChannelHandlerContext, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture disconnect();
 
     /**
      * Request to close the {@link Channel} and notify the {@link ChannelFuture} once the operation completes,
      * either because the operation was successful or because of
      * an error.
      *
      * After it is closed it is not possible to reuse it again.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#close(ChannelHandlerContext, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture close();
 
     /**
      * Request to deregister from the previous assigned {@link EventExecutor} and notify the
      * {@link ChannelFuture} once the operation completes, either because the operation was successful or because of
      * an error.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#deregister(ChannelHandlerContext, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      *
      */
     ChannelFuture deregister();
 
     /**
      * Request to bind to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation
      * completes, either because the operation was successful or because of an error.
      *
      * The given {@link ChannelPromise} will be notified.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#bind(ChannelHandlerContext, SocketAddress, ChannelPromise)} method
      * called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture bind(SocketAddress localAddress, ChannelPromise promise);
 
     /**
      * Request to connect to the given {@link SocketAddress} and notify the {@link ChannelFuture} once the operation
      * completes, either because the operation was successful or because of an error.
      *
      * The given {@link ChannelFuture} will be notified.
      *
      * <p>
      * If the connection fails because of a connection timeout, the {@link ChannelFuture} will get failed with
      * a {@link ConnectTimeoutException}. If it fails because of connection refused a {@link ConnectException}
      * will be used.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture connect(SocketAddress remoteAddress, ChannelPromise promise);
 
     /**
      * Request to connect to the given {@link SocketAddress} while bind to the localAddress and notify the
      * {@link ChannelFuture} once the operation completes, either because the operation was successful or because of
      * an error.
      *
      * The given {@link ChannelPromise} will be notified and also returned.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture connect(SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise);
 
     /**
      * Request to disconnect from the remote peer and notify the {@link ChannelFuture} once the operation completes,
      * either because the operation was successful or because of an error.
      *
      * The given {@link ChannelPromise} will be notified.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#disconnect(ChannelHandlerContext, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture disconnect(ChannelPromise promise);
 
     /**
      * Request to close the {@link Channel} and notify the {@link ChannelFuture} once the operation completes,
      * either because the operation was successful or because of
      * an error.
      *
      * After it is closed it is not possible to reuse it again.
      * The given {@link ChannelPromise} will be notified.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#close(ChannelHandlerContext, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture close(ChannelPromise promise);
 
     /**
      * Request to deregister from the previous assigned {@link EventExecutor} and notify the
      * {@link ChannelFuture} once the operation completes, either because the operation was successful or because of
      * an error.
      *
      * The given {@link ChannelPromise} will be notified.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#deregister(ChannelHandlerContext, ChannelPromise)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelFuture deregister(ChannelPromise promise);
 
     /**
      * Request to Read data from the {@link Channel} into the first inbound buffer, triggers an
      * {@link ChannelInboundHandler#channelRead(ChannelHandlerContext, Object)} event if data was
      * read, and triggers a
      * {@link ChannelInboundHandler#channelReadComplete(ChannelHandlerContext) channelReadComplete} event so the
      * handler can decide to continue reading.  If there's a pending read operation already, this method does nothing.
      * <p>
      * This will result in having the
      * {@link ChannelOutboundHandler#read(ChannelHandlerContext)}
      * method called of the next {@link ChannelOutboundHandler} contained in the  {@link ChannelPipeline} of the
      * {@link Channel}.
      */
     ChannelHandlerContext read();
 
     /**
      * Request to write a message via this {@link ChannelHandlerContext} through the {@link ChannelPipeline}.
      * This method will not request to actual flush, so be sure to call {@link #flush()}
      * once you want to request to flush all pending data to the actual transport.
      */
     ChannelFuture write(Object msg);
 
     /**
      * Request to write a message via this {@link ChannelHandlerContext} through the {@link ChannelPipeline}.
      * This method will not request to actual flush, so be sure to call {@link #flush()}
      * once you want to request to flush all pending data to the actual transport.
      */
     ChannelFuture write(Object msg, ChannelPromise promise);
 
     /**
      * Request to flush all pending messages via this ChannelOutboundInvoker.
      */
     ChannelHandlerContext flush();
 
     /**
      * Shortcut for call {@link #write(Object, ChannelPromise)} and {@link #flush()}.
      */
     ChannelFuture writeAndFlush(Object msg, ChannelPromise promise);
 
     /**
      * Shortcut for call {@link #write(Object)} and {@link #flush()}.
      */
     ChannelFuture writeAndFlush(Object msg);
 
     /**
      * Return the assigned {@link ChannelPipeline}
      */
     ChannelPipeline pipeline();
 
     /**
      * Return the assigned {@link ByteBufAllocator} which will be used to allocate {@link ByteBuf}s.
      */
     ByteBufAllocator alloc();
 
     /**
      * Return a new {@link ChannelPromise}.
      */
     ChannelPromise newPromise();
 
     /**
      * Return an new {@link ChannelProgressivePromise}
      */
     ChannelProgressivePromise newProgressivePromise();
 
     /**
      * Create a new {@link ChannelFuture} which is marked as succeeded already. So {@link ChannelFuture#isSuccess()}
      * will return {@code true}. All {@link FutureListener} added to it will be notified directly. Also
      * every call of blocking methods will just return without blocking.
      */
     ChannelFuture newSucceededFuture();
 
     /**
      * Create a new {@link ChannelFuture} which is marked as failed already. So {@link ChannelFuture#isSuccess()}
      * will return {@code false}. All {@link FutureListener} added to it will be notified directly. Also
      * every call of blocking methods will just return without blocking.
      */
     ChannelFuture newFailedFuture(Throwable cause);
 
     /**
      * Return a special ChannelPromise which can be reused for different operations.
      * <p>
      * It's only supported to use
      * it for {@link ChannelHandlerContext#write(Object, ChannelPromise)}.
      * </p>
      * <p>
      * Be aware that the returned {@link ChannelPromise} will not support most operations and should only be used
      * if you want to save an object allocation for every write operation. You will not be able to detect if the
      * operation  was complete, only if it failed as the implementation will call
      * {@link ChannelPipeline#fireExceptionCaught(Throwable)} in this case.
      * </p>
      * <strong>Be aware this is an expert feature and should be used with care!</strong>
      */
     ChannelPromise voidPromise();
 
 }