/*
 * 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 common.net.handler.timeout;

import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

import common.net.channel.ChannelHandlerContext;
import common.net.channel.ChannelInboundHandlerAdapter;

/**
 * Raises a {@link ReadTimeoutException} when no data was read within a certain
 * period of time.
 *
 * <pre>
 * // The connection is closed when there is no inbound traffic
 * // for 30 seconds.
 *
 * public class MyChannelInitializer extends {@link ChannelInitializer}&lt{@link Channel}&gt {
 *     public void initChannel({@link Channel} channel) {
 *         channel.pipeline().addLast("readTimeoutHandler", new {@link ReadTimeoutHandler}(30);
 *         channel.pipeline().addLast("myHandler", new MyHandler());
 *     }
 * }
 *
 * // Handler should handle the {@link ReadTimeoutException}.
 * public class MyHandler extends {@link ChannelDuplexHandler} {
 *     {@code @Override}
 *     public void exceptionCaught({@link ChannelHandlerContext} ctx, {@link Throwable} cause)
 *             throws {@link Exception} {
 *         if (cause instanceof {@link ReadTimeoutException}) {
 *             // do something
 *         } else {
 *             super.exceptionCaught(ctx, cause);
 *         }
 *     }
 * }
 *
 * {@link ServerBootstrap} bootstrap = ...;
 * ...
 * bootstrap.childHandler(new MyChannelInitializer());
 * ...
 * </pre>
 * @see WriteTimeoutHandler
 * @see IdleStateHandler
 */
public class ReadTimeoutHandler extends ChannelInboundHandlerAdapter {
    private static final long MIN_TIMEOUT_NANOS = TimeUnit.MILLISECONDS.toNanos(1);

    private final long timeoutNanos;

    private volatile ScheduledFuture<?> timeout;
    private volatile long lastReadTime;

    private volatile int state; // 0 - none, 1 - Initialized, 2 - Destroyed;

    private boolean closed;

    /**
     * Creates a new instance.
     *
     * @param timeoutSeconds
     *        read timeout in seconds
     */
    public ReadTimeoutHandler(int timeoutSeconds) {
        this(timeoutSeconds, TimeUnit.SECONDS);
    }

    /**
     * Creates a new instance.
     *
     * @param timeout
     *        read timeout
     * @param unit
     *        the {@link TimeUnit} of {@code timeout}
     */
    public ReadTimeoutHandler(long timeout, TimeUnit unit) {
        if (unit == null) {
            throw new NullPointerException("unit");
        }

        if (timeout <= 0) {
            timeoutNanos = 0;
        } else {
            timeoutNanos = Math.max(unit.toNanos(timeout), MIN_TIMEOUT_NANOS);
        }
    }

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        if (ctx.channel().isActive() && ctx.channel().isRegistered()) {
            // channelActvie() event has been fired already, which means this.channelActive() will
            // not be invoked. We have to initialize here instead.
            initialize(ctx);
        } else {
            // channelActive() event has not been fired yet.  this.channelActive() will be invoked
            // and initialization will occur there.
        }
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        destroy();
    }

    @Override
    public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        // Initialize early if channel is active already.
        if (ctx.channel().isActive()) {
            initialize(ctx);
        }
        super.channelRegistered(ctx);
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        // This method will be invoked only if this handler was added
        // before channelActive() event is fired.  If a user adds this handler
        // after the channelActive() event, initialize() will be called by beforeAdd().
        initialize(ctx);
        super.channelActive(ctx);
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        destroy();
        super.channelInactive(ctx);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        lastReadTime = System.nanoTime();
        ctx.fireChannelRead(msg);
    }

    private void initialize(ChannelHandlerContext ctx) {
        // Avoid the case where destroy() is called before scheduling timeouts.
        // See: https://github.com/netty/netty/issues/143
        switch (state) {
        case 1:
        case 2:
            return;
        }

        state = 1;

        lastReadTime = System.nanoTime();
        if (timeoutNanos > 0) {
            timeout = ctx.executor().schedule(
                    new ReadTimeoutTask(ctx),
                    timeoutNanos, TimeUnit.NANOSECONDS);
        }
    }

    private void destroy() {
        state = 2;

        if (timeout != null) {
            timeout.cancel(false);
            timeout = null;
        }
    }

    /**
     * Is called when a read timeout was detected.
     */
    protected void readTimedOut(ChannelHandlerContext ctx) throws Exception {
        if (!closed) {
            ctx.fireExceptionCaught(ReadTimeoutException.INSTANCE);
            ctx.close();
            closed = true;
        }
    }

    private final class ReadTimeoutTask implements Runnable {

        private final ChannelHandlerContext ctx;

        ReadTimeoutTask(ChannelHandlerContext ctx) {
            this.ctx = ctx;
        }

        @Override
        public void run() {
            if (!ctx.channel().isOpen()) {
                return;
            }

            long currentTime = System.nanoTime();
            long nextDelay = timeoutNanos - (currentTime - lastReadTime);
            if (nextDelay <= 0) {
                // Read timed out - set a new timeout and notify the callback.
                timeout = ctx.executor().schedule(this, timeoutNanos, TimeUnit.NANOSECONDS);
                try {
                    readTimedOut(ctx);
                } catch (Throwable t) {
                    ctx.fireExceptionCaught(t);
                }
            } else {
                // Read occurred before the timeout - set a new timeout with shorter delay.
                timeout = ctx.executor().schedule(this, nextDelay, TimeUnit.NANOSECONDS);
            }
        }
    }
}
