/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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.apache.activemq.transport;

import java.io.IOException;
import java.util.Timer;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.activemq.command.KeepAliveInfo;
import org.apache.activemq.command.WireFormatInfo;
import org.apache.activemq.thread.SchedulerTimerTask;
import org.apache.activemq.wireformat.WireFormat;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Used to make sure that commands are arriving periodically from the peer of
 * the transport.
 *
 *
 */
public class InactivityMonitor extends TransportFilter {

    private static final Logger LOG = LoggerFactory.getLogger(InactivityMonitor.class);
    private static ThreadPoolExecutor ASYNC_TASKS;
    private static int CHECKER_COUNTER;
    private static long DEFAULT_CHECK_TIME_MILLS = 30000;
    private static Timer  READ_CHECK_TIMER;
    private static Timer  WRITE_CHECK_TIMER;

    private WireFormatInfo localWireFormatInfo;
    private WireFormatInfo remoteWireFormatInfo;
    private final AtomicBoolean monitorStarted = new AtomicBoolean(false);

    private final AtomicBoolean commandSent = new AtomicBoolean(false);
    private final AtomicBoolean inSend = new AtomicBoolean(false);
    private final AtomicBoolean failed = new AtomicBoolean(false);

    private final AtomicBoolean commandReceived = new AtomicBoolean(true);
    private final AtomicBoolean inReceive = new AtomicBoolean(false);
    private final AtomicInteger lastReceiveCounter = new AtomicInteger(0);

    private SchedulerTimerTask writeCheckerTask;
    private SchedulerTimerTask readCheckerTask;

    private boolean ignoreRemoteWireFormat = false;
    private boolean ignoreAllWireFormatInfo = false;

    private long readCheckTime = DEFAULT_CHECK_TIME_MILLS;
    private long writeCheckTime = DEFAULT_CHECK_TIME_MILLS;
    private long initialDelayTime = DEFAULT_CHECK_TIME_MILLS;
    private boolean useKeepAlive = true;
    private boolean keepAliveResponseRequired;
    private WireFormat wireFormat;

    private final Runnable readChecker = new Runnable() {
        long lastRunTime;
        public void run() {
            long now = System.currentTimeMillis();
            long elapsed = (now-lastRunTime);

            if( lastRunTime != 0 && LOG.isDebugEnabled() ) {
                LOG.debug(""+elapsed+" ms elapsed since last read check.");
            }

            // Perhaps the timer executed a read check late.. and then executes
            // the next read check on time which causes the time elapsed between
            // read checks to be small..

            // If less than 90% of the read check Time elapsed then abort this readcheck.
            if( !allowReadCheck(elapsed) ) { // FUNKY qdox bug does not allow me to inline this expression.
                LOG.debug("Aborting read check.. Not enough time elapsed since last read check.");
                return;
            }

            lastRunTime = now;
            readCheck();
        }
    };

    private boolean allowReadCheck(long elapsed) {
        return elapsed > (readCheckTime * 9 / 10);
    }

    private final Runnable writeChecker = new Runnable() {
        long lastRunTime;
        public void run() {
            long now = System.currentTimeMillis();
            if( lastRunTime != 0 && LOG.isDebugEnabled() ) {
                LOG.debug(this + " "+(now-lastRunTime)+" ms elapsed since last write check.");

            }
            lastRunTime = now;
            writeCheck();
        }
    };

    public InactivityMonitor(Transport next, WireFormat wireFormat) {
        super(next);
        this.wireFormat = wireFormat;
        if (this.wireFormat == null) {
            this.ignoreAllWireFormatInfo = true;
        }
    }

    public void start() throws Exception {
        next.start();
        startMonitorThreads();
    }

    public void stop() throws Exception {
        stopMonitorThreads();
        next.stop();
    }

    final void writeCheck() {
        if (inSend.get()) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("A send is in progress");
            }
            return;
        }

        if (!commandSent.get() && useKeepAlive) {
            if (LOG.isTraceEnabled()) {
                LOG.trace(this + " no message sent since last write check, sending a KeepAliveInfo");
            }
            ASYNC_TASKS.execute(new Runnable() {
                public void run() {
                    if (monitorStarted.get()) {
                        try {

                            KeepAliveInfo info = new KeepAliveInfo();
                            info.setResponseRequired(keepAliveResponseRequired);
                            oneway(info);
                        } catch (IOException e) {
                            onException(e);
                        }
                    }
                };
            });
        } else {
            if (LOG.isTraceEnabled()) {
                LOG.trace(this + " message sent since last write check, resetting flag");
            }
        }

        commandSent.set(false);
    }

    final void readCheck() {
        int currentCounter = next.getReceiveCounter();
        int previousCounter = lastReceiveCounter.getAndSet(currentCounter);
        if (inReceive.get() || currentCounter!=previousCounter ) {
            if (LOG.isTraceEnabled()) {
                LOG.trace("A receive is in progress");
            }
            return;
        }
        if (!commandReceived.get()) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("No message received since last read check for " + toString() + "! Throwing InactivityIOException.");
            }
            ASYNC_TASKS.execute(new Runnable() {
                public void run() {
                    onException(new InactivityIOException("Channel was inactive for too (>" + readCheckTime + ") long: "+next.getRemoteAddress()));
                };

            });
        } else {
            if (LOG.isTraceEnabled()) {
                LOG.trace("Message received since last read check, resetting flag: ");
            }
        }
        commandReceived.set(false);
    }

    public void onCommand(Object command) {
        commandReceived.set(true);
        inReceive.set(true);
        try {
            if (command.getClass() == KeepAliveInfo.class) {
                KeepAliveInfo info = (KeepAliveInfo) command;
                if (info.isResponseRequired()) {
                    try {
                        info.setResponseRequired(false);
                        oneway(info);
                    } catch (IOException e) {
                        onException(e);
                    }
                }
            } else {
                if (command.getClass() == WireFormatInfo.class) {
                    synchronized (this) {
                        IOException error = null;
                        remoteWireFormatInfo = (WireFormatInfo) command;
                        try {
                            startMonitorThreads();
                        } catch (IOException e) {
                            error = e;
                        }
                        if (error != null) {
                            onException(error);
                        }
                    }
                }
                synchronized (readChecker) {
                    transportListener.onCommand(command);
                }
            }
        } finally {

            inReceive.set(false);
        }
    }

    public void oneway(Object o) throws IOException {
        // Disable inactivity monitoring while processing a command.
        //synchronize this method - its not synchronized
        //further down the transport stack and gets called by more
        //than one thread  by this class
        synchronized(inSend) {
            inSend.set(true);
            try {

                if( failed.get() ) {
                    throw new InactivityIOException("Cannot send, channel has already failed: "+next.getRemoteAddress());
                }
                if (o.getClass() == WireFormatInfo.class) {
                    synchronized (this) {
                        localWireFormatInfo = (WireFormatInfo)o;
                        startMonitorThreads();
                    }
                }
                next.oneway(o);
            } finally {
                commandSent.set(true);
                inSend.set(false);
            }
        }
    }

    public void onException(IOException error) {
        if (failed.compareAndSet(false, true)) {
            stopMonitorThreads();
            transportListener.onException(error);
        }
    }

    public void setKeepAliveResponseRequired(boolean val) {
        keepAliveResponseRequired = val;
    }

    public void setUseKeepAlive(boolean val) {
        useKeepAlive = val;
    }

    public void setIgnoreRemoteWireFormat(boolean val) {
        ignoreRemoteWireFormat = val;
    }

    public long getReadCheckTime() {
        return readCheckTime;
    }

    public void setReadCheckTime(long readCheckTime) {
        this.readCheckTime = readCheckTime;
    }

    public long getInitialDelayTime() {
        return initialDelayTime;
    }

    public void setInitialDelayTime(long initialDelayTime) {
        this.initialDelayTime = initialDelayTime;
    }

    private synchronized void startMonitorThreads() throws IOException {
        if (monitorStarted.get()) {
            return;
        }

        if (!configuredOk()) {
            return;
        }

        if (readCheckTime > 0) {
            monitorStarted.set(true);
            writeCheckerTask = new SchedulerTimerTask(writeChecker);
            readCheckerTask = new  SchedulerTimerTask(readChecker);
            writeCheckTime = readCheckTime>3 ? readCheckTime/3 : readCheckTime;
            synchronized( InactivityMonitor.class ) {
                if( CHECKER_COUNTER == 0 ) {
                    ASYNC_TASKS = createExecutor();
                    READ_CHECK_TIMER = new Timer("InactivityMonitor ReadCheck",true);
                    WRITE_CHECK_TIMER = new Timer("InactivityMonitor WriteCheck",true);
                }
                CHECKER_COUNTER++;
                WRITE_CHECK_TIMER.scheduleAtFixedRate(writeCheckerTask, initialDelayTime,writeCheckTime);
                READ_CHECK_TIMER.scheduleAtFixedRate(readCheckerTask, initialDelayTime,readCheckTime);
            }
        }
    }

    private boolean configuredOk() throws IOException {
        boolean configured = false;
        if (ignoreAllWireFormatInfo) {
            configured = true;
        } else if (localWireFormatInfo != null && remoteWireFormatInfo != null) {
            if (!ignoreRemoteWireFormat) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Using min of local: " + localWireFormatInfo + " and remote: " + remoteWireFormatInfo);
                }
                readCheckTime = Math.min(localWireFormatInfo.getMaxInactivityDuration(), remoteWireFormatInfo.getMaxInactivityDuration());
                initialDelayTime = Math.min(localWireFormatInfo.getMaxInactivityDurationInitalDelay(), remoteWireFormatInfo.getMaxInactivityDurationInitalDelay());
            } else {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Using local: " + localWireFormatInfo);
                }
                readCheckTime = localWireFormatInfo.getMaxInactivityDuration();
                initialDelayTime = localWireFormatInfo.getMaxInactivityDurationInitalDelay();
            }
            configured = true;
        }
        return configured;
    }

    /**
     *
     */
    private synchronized void stopMonitorThreads() {
        if (monitorStarted.compareAndSet(true, false)) {
            readCheckerTask.cancel();
            writeCheckerTask.cancel();
            synchronized( InactivityMonitor.class ) {
                WRITE_CHECK_TIMER.purge();
                READ_CHECK_TIMER.purge();
                CHECKER_COUNTER--;
                if(CHECKER_COUNTER==0) {
                    WRITE_CHECK_TIMER.cancel();
                    READ_CHECK_TIMER.cancel();
                    WRITE_CHECK_TIMER = null;
                    READ_CHECK_TIMER = null;
                    ASYNC_TASKS.shutdownNow();
                    ASYNC_TASKS = null;
                }
            }
        }
    }

    private ThreadFactory factory = new ThreadFactory() {
        public Thread newThread(Runnable runnable) {
            Thread thread = new Thread(runnable, "InactivityMonitor Async Task: "+runnable);
            thread.setDaemon(true);
            return thread;
        }
    };

    private ThreadPoolExecutor createExecutor() {
        ThreadPoolExecutor exec = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 10, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), factory);
        exec.allowCoreThreadTimeOut(true);
        return exec;
    }
}
