/*
    * 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 org.jboss.netty.handler.timeout;
  
  import org.jboss.netty.bootstrap.ServerBootstrap;
  import org.jboss.netty.channel.ChannelHandler;
  import org.jboss.netty.channel.ChannelHandler.Sharable;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.channel.ChannelPipeline;
  import org.jboss.netty.channel.ChannelPipelineFactory;
  import org.jboss.netty.channel.ChannelStateEvent;
  import org.jboss.netty.channel.Channels;
  import org.jboss.netty.channel.LifeCycleAwareChannelHandler;
  import org.jboss.netty.channel.MessageEvent;
  import org.jboss.netty.channel.SimpleChannelUpstreamHandler;
  import org.jboss.netty.util.ExternalResourceReleasable;
  import org.jboss.netty.util.HashedWheelTimer;
  import org.jboss.netty.util.Timeout;
  import org.jboss.netty.util.Timer;
  import org.jboss.netty.util.TimerTask;
  
  import java.util.concurrent.TimeUnit;
  
  import static org.jboss.netty.channel.Channels.*;
  
  /**
   * Raises a {@link ReadTimeoutException} when no data was read within a certain
   * period of time.
   *
   * <pre>
   * public class MyPipelineFactory implements {@link ChannelPipelineFactory} {
   *
   *     private final {@link Timer} timer;
   *     private final {@link ChannelHandler} timeoutHandler;
   *
   *     public MyPipelineFactory({@link Timer} timer) {
   *         this.timer = timer;
   *         this.timeoutHandler = <b>new {@link ReadTimeoutHandler}(timer, 30), // timer must be shared.</b>
   *     }
   *
   *     public {@link ChannelPipeline} getPipeline() {
   *         // An example configuration that implements 30-second read timeout:
   *         return {@link Channels}.pipeline(
   *             timeoutHandler,
   *             new MyHandler());
   *     }
   * }
   *
   * {@link ServerBootstrap} bootstrap = ...;
   * {@link Timer} timer = new {@link HashedWheelTimer}();
   * ...
   * bootstrap.setPipelineFactory(new MyPipelineFactory(timer));
   * ...
   * </pre>
   *
   * The {@link Timer} which was specified when the {@link ReadTimeoutHandler} is
   * created should be stopped manually by calling {@link #releaseExternalResources()}
   * or {@link Timer#stop()} when your application shuts down.
   * @see WriteTimeoutHandler
   * @see IdleStateHandler
   *
   * @apiviz.landmark
   * @apiviz.uses org.jboss.netty.util.HashedWheelTimer
   * @apiviz.has org.jboss.netty.handler.timeout.TimeoutException oneway - - raises
   */
  @Sharable
  public class ReadTimeoutHandler extends SimpleChannelUpstreamHandler
                                  implements LifeCycleAwareChannelHandler,
                                             ExternalResourceReleasable {
  
      static final ReadTimeoutException EXCEPTION = new ReadTimeoutException();
  
      final Timer timer;
      final long timeoutMillis;
  
      /**
       * Creates a new instance.
       *
       * @param timer
       *        the {@link Timer} that is used to trigger the scheduled event.
       *        The recommended {@link Timer} implementation is {@link HashedWheelTimer}.
       * @param timeoutSeconds
       *        read timeout in seconds
       */
      public ReadTimeoutHandler(Timer timer, int timeoutSeconds) {
          this(timer, timeoutSeconds, TimeUnit.SECONDS);
     }
 
     /**
      * Creates a new instance.
      *
      * @param timer
      *        the {@link Timer} that is used to trigger the scheduled event.
      *        The recommended {@link Timer} implementation is {@link HashedWheelTimer}.
      * @param timeout
      *        read timeout
      * @param unit
      *        the {@link TimeUnit} of {@code timeout}
      */
     public ReadTimeoutHandler(Timer timer, long timeout, TimeUnit unit) {
         if (timer == null) {
             throw new NullPointerException("timer");
         }
         if (unit == null) {
             throw new NullPointerException("unit");
         }
 
         this.timer = timer;
         if (timeout <= 0) {
             timeoutMillis = 0;
         } else {
             timeoutMillis = Math.max(unit.toMillis(timeout), 1);
         }
     }
 
     /**
      * Stops the {@link Timer} which was specified in the constructor of this
      * handler.  You should not call this method if the {@link Timer} is in use
      * by other objects.
      */
     public void releaseExternalResources() {
         timer.stop();
     }
 
     public void beforeAdd(ChannelHandlerContext ctx) throws Exception {
         if (ctx.getPipeline().isAttached()) {
             // channelOpen event has been fired already, which means
             // this.channelOpen() will not be invoked.
             // We have to initialize here instead.
             initialize(ctx);
         } else {
             // channelOpen event has not been fired yet.
             // this.channelOpen() will be invoked and initialization will occur there.
         }
     }
 
     public void afterAdd(ChannelHandlerContext ctx) throws Exception {
         // NOOP
     }
 
     public void beforeRemove(ChannelHandlerContext ctx) throws Exception {
         destroy(ctx);
     }
 
     public void afterRemove(ChannelHandlerContext ctx) throws Exception {
         // NOOP
     }
 
     @Override
     public void channelOpen(ChannelHandlerContext ctx, ChannelStateEvent e)
             throws Exception {
         // This method will be invoked only if this handler was added
         // before channelOpen event is fired.  If a user adds this handler
         // after the channelOpen event, initialize() will be called by beforeAdd().
         initialize(ctx);
         ctx.sendUpstream(e);
     }
 
     @Override
     public void channelClosed(ChannelHandlerContext ctx, ChannelStateEvent e)
             throws Exception {
         destroy(ctx);
         ctx.sendUpstream(e);
     }
 
     @Override
     public void messageReceived(ChannelHandlerContext ctx, MessageEvent e)
             throws Exception {
         State state = (State) ctx.getAttachment();
         state.lastReadTime = System.currentTimeMillis();
         ctx.sendUpstream(e);
     }
 
     private void initialize(ChannelHandlerContext ctx) {
         State state = state(ctx);
 
         // Avoid the case where destroy() is called before scheduling timeouts.
         // See: https://github.com/netty/netty/issues/143
         synchronized (state) {
             switch (state.state) {
             case 1:
             case 2:
                 return;
             }
             state.state = 1;
         }
 
         if (timeoutMillis > 0) {
             state.timeout = timer.newTimeout(new ReadTimeoutTask(ctx), timeoutMillis, TimeUnit.MILLISECONDS);
         }
     }
 
     private static void destroy(ChannelHandlerContext ctx) {
         State state = state(ctx);
         synchronized (state) {
             if (state.state != 1) {
                 return;
             }
             state.state = 2;
         }
 
         if (state.timeout != null) {
             state.timeout.cancel();
             state.timeout = null;
         }
     }
 
     private static State state(ChannelHandlerContext ctx) {
         State state;
         synchronized (ctx) {
             // FIXME: It could have been better if there is setAttachmentIfAbsent().
             state = (State) ctx.getAttachment();
             if (state != null) {
                 return state;
             }
             state = new State();
             ctx.setAttachment(state);
         }
         return state;
     }
 
     protected void readTimedOut(ChannelHandlerContext ctx) throws Exception {
         fireExceptionCaught(ctx, EXCEPTION);
     }
 
     private final class ReadTimeoutTask implements TimerTask {
 
         private final ChannelHandlerContext ctx;
 
         ReadTimeoutTask(ChannelHandlerContext ctx) {
             this.ctx = ctx;
         }
 
         public void run(Timeout timeout) throws Exception {
             if (timeout.isCancelled()) {
                 return;
             }
 
             if (!ctx.getChannel().isOpen()) {
                 return;
             }
 
             State state = (State) ctx.getAttachment();
             long currentTime = System.currentTimeMillis();
             long nextDelay = timeoutMillis - (currentTime - state.lastReadTime);
             if (nextDelay <= 0) {
                 // Read timed out - set a new timeout and notify the callback.
                 state.timeout =
                     timer.newTimeout(this, timeoutMillis, TimeUnit.MILLISECONDS);
                 fireReadTimedOut(ctx);
             } else {
                 // Read occurred before the timeout - set a new timeout with shorter delay.
                 state.timeout =
                     timer.newTimeout(this, nextDelay, TimeUnit.MILLISECONDS);
             }
         }
 
         private void fireReadTimedOut(final ChannelHandlerContext ctx) throws Exception {
             ctx.getPipeline().execute(new Runnable() {
 
                 public void run() {
                     try {
                         readTimedOut(ctx);
                     } catch (Throwable t) {
                         fireExceptionCaught(ctx, t);
                     }
                 }
             });
         }
     }
 
     private static final class State {
         // 0 - none, 1 - initialized, 2 - destroyed
         int state;
         volatile Timeout timeout;
         volatile long lastReadTime = System.currentTimeMillis();
 
         State() {
         }
     }
 }