/*
 * 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.Attribute;
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. Among other things a handler can notify the next {@link ChannelHandler} in the
 * {@link ChannelPipeline} as well as 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 ChannelHandlerAdapter} {
 *
 *     <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 ChannelHandlerAdapter} {
 *
 *   private final {@link AttributeKey}&lt;{@link Integer}&gt; counter = {@link AttributeKey}.valueOf("counter");
 *
 *   // This handler will receive a sequence of increasing integers starting
 *   // from 1.
 *   {@code @Override}
 *   public void channelRead({@link ChannelHandlerContext} ctx, Object msg) {
 *     {@link Attribute}&lt;{@link Integer}&gt; attr = ctx.getAttr(counter);
 *     Integer a = ctx.getAttr(counter).get();
 *
 *     if (a == null) {
 *       a = 1;
 *     }
 *
 *     attr.set(a * (Integer) msg);
 *   }
 * }
 *
 * // 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 (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();

    /**
     * Returns the {@link EventExecutor} which is used to execute an arbitrary task.
     */
    EventExecutor executor();

    /**
     * Returns the {@link ChannelHandlerInvoker} which is used to trigger an event for the associated
     * {@link ChannelHandler}. Note that the methods in {@link ChannelHandlerInvoker} are not intended to be called
     * by a user. Use this method only to obtain the reference to the {@link ChannelHandlerInvoker}
     * (and not calling its methods) unless you know what you are doing.
     */
    ChannelHandlerInvoker invoker();

    /**
     * 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 {@link ChannelHandler} 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 ChannelHandler#channelRegistered(ChannelHandlerContext)} method
     * called of the next {@link ChannelHandler} 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 ChannelHandler#channelUnregistered(ChannelHandlerContext)} method
     * called of the next {@link ChannelHandler} 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 ChannelHandler#channelActive(ChannelHandlerContext)} method
     * called of the next {@link ChannelHandler} 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 ChannelHandler#channelInactive(ChannelHandlerContext)} method
     * called of the next {@link ChannelHandler} 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 ChannelHandler#exceptionCaught(ChannelHandlerContext, Throwable)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#userEventTriggered(ChannelHandlerContext, Object)}
     * method called of the next {@link ChannelHandler} contained in the {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelHandlerContext fireUserEventTriggered(Object event);

    /**
     * A {@link Channel} received a message.
     *
     * This will result in having the {@link ChannelHandler#channelRead(ChannelHandlerContext, Object)}
     * method called of the next {@link ChannelHandler} contained in the {@link ChannelPipeline} of the
     * {@link Channel}.
     */
    ChannelHandlerContext fireChannelRead(Object msg);

    /**
     * Triggers an {@link ChannelHandler#channelReadComplete(ChannelHandlerContext)}
     * event to the next {@link ChannelHandler} in the {@link ChannelPipeline}.
     */
    ChannelHandlerContext fireChannelReadComplete();

    /**
     * Triggers an {@link ChannelHandler#channelWritabilityChanged(ChannelHandlerContext)}
     * event to the next {@link ChannelHandler} 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 ChannelHandler#bind(ChannelHandlerContext, SocketAddress, ChannelPromise)} method
     * called of the next {@link ChannelHandler} 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 ChannelHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#disconnect(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#close(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#deregister(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#bind(ChannelHandlerContext, SocketAddress, ChannelPromise)} method
     * called of the next {@link ChannelHandler} 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 ChannelHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#disconnect(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#close(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#deregister(ChannelHandlerContext, ChannelPromise)}
     * method called of the next {@link ChannelHandler} 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 ChannelHandler#channelRead(ChannelHandlerContext, Object)} event if data was
     * read, and triggers a
     * {@link ChannelHandler#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 ChannelHandler#read(ChannelHandlerContext)}
     * method called of the next {@link ChannelHandler} 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();

}
