// ========================================================================
   // Copyright (c) 2004-2009 Mort Bay Consulting Pty. Ltd.
   // ------------------------------------------------------------------------
   // All rights reserved. This program and the accompanying materials
   // are made available under the terms of the Eclipse Public License v1.0
   // and Apache License v2.0 which accompanies this distribution.
   // The Eclipse Public License is available at 
   // http://www.eclipse.org/legal/epl-v10.html
   // The Apache License v2.0 is available at
  // http://www.opensource.org/licenses/apache2.0.php
  // You may elect to redistribute this code under either of these licenses. 
  // ========================================================================
  
  package org.eclipse.jetty.util.thread;
  
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  
  
  /* ------------------------------------------------------------ */
  /** Timeout queue.
   * This class implements a timeout queue for timers that are at least as likely to be cancelled as they are to expire.
   * Unlike the util timeout class, the duration of the timeouts is shared by all scheduled tasks and if the duration 
   * is changed, this affects all scheduled tasks.
   * <p>
   * The nested class Task should be extended by users of this class to obtain call back notification of 
   * expires. 
   */
  public class Timeout
  {
      private static final Logger LOG = Log.getLogger(Timeout.class);
      private Object _lock;
      private long _duration;
      private volatile long _now=System.currentTimeMillis();
      private Task _head=new Task();
  
      /* ------------------------------------------------------------ */
      public Timeout()
      {
          _lock=new Object();
          _head._timeout=this;
      }
  
      /* ------------------------------------------------------------ */
      public Timeout(Object lock)
      {
          _lock=lock;
          _head._timeout=this;
      }
  
      /* ------------------------------------------------------------ */
      /**
       * @return Returns the duration.
       */
      public long getDuration()
      {
          return _duration;
      }
  
      /* ------------------------------------------------------------ */
      /**
       * @param duration The duration to set.
       */
      public void setDuration(long duration)
      {
          _duration = duration;
      }
  
      /* ------------------------------------------------------------ */
      public long setNow()
      {
          return _now=System.currentTimeMillis();
      }
      
      /* ------------------------------------------------------------ */
      public long getNow()
      {
          return _now;
      }
  
      /* ------------------------------------------------------------ */
      public void setNow(long now)
      {
          _now=now;
      }
  
      /* ------------------------------------------------------------ */
      /** Get an expired tasks.
       * This is called instead of {@link #tick()} to obtain the next
       * expired Task, but without calling it's {@link Task#expire()} or
       * {@link Task#expired()} methods.
       * 
       * @return the next expired task or null.
       */
      public Task expired()
      {
          synchronized (_lock)
          {
              long _expiry = _now-_duration;
 
             if (_head._next!=_head)
             {
                 Task task = _head._next;
                 if (task._timestamp>_expiry)
                     return null;
 
                 task.unlink();
                 task._expired=true;
                 return task;
             }
             return null;
         }
     }
 
     /* ------------------------------------------------------------ */
     public void tick()
     {
         final long expiry = _now-_duration;
 
         Task task=null;
         while (true)
         {
             try
             {
                 synchronized (_lock)
                 {
                     task= _head._next;
                     if (task==_head || task._timestamp>expiry)
                         break;
                     task.unlink();
                     task._expired=true;
                     task.expire();
                 }
                 
                 task.expired();
             }
             catch(Throwable th)
             {
                 LOG.warn(Log.EXCEPTION,th);
             }
         }
     }
 
     /* ------------------------------------------------------------ */
     public void tick(long now)
     {
         _now=now;
         tick();
     }
 
     /* ------------------------------------------------------------ */
     public void schedule(Task task)
     {
         schedule(task,0L);
     }
     
     /* ------------------------------------------------------------ */
     /**
      * @param task
      * @param delay A delay in addition to the default duration of the timeout
      */
     public void schedule(Task task,long delay)
     {
         synchronized (_lock)
         {
             if (task._timestamp!=0)
             {
                 task.unlink();
                 task._timestamp=0;
             }
             task._timeout=this;
             task._expired=false;
             task._delay=delay;
             task._timestamp = _now+delay;
 
             Task last=_head._prev;
             while (last!=_head)
             {
                 if (last._timestamp <= task._timestamp)
                     break;
                 last=last._prev;
             }
             last.link(task);
         }
     }
 
 
     /* ------------------------------------------------------------ */
     public void cancelAll()
     {
         synchronized (_lock)
         {
             _head._next=_head._prev=_head;
         }
     }
 
     /* ------------------------------------------------------------ */
     public boolean isEmpty()
     {
         synchronized (_lock)
         {
             return _head._next==_head;
         }
     }
 
     /* ------------------------------------------------------------ */
     public long getTimeToNext()
     {
         synchronized (_lock)
         {
             if (_head._next==_head)
                 return -1;
             long to_next = _duration+_head._next._timestamp-_now;
             return to_next<0?0:to_next;
         }
     }
 
     /* ------------------------------------------------------------ */
     @Override
     public String toString()
     {
         StringBuffer buf = new StringBuffer();
         buf.append(super.toString());
         
         Task task = _head._next;
         while (task!=_head)
         {
             buf.append("-->");
             buf.append(task);
             task=task._next;
         }
         
         return buf.toString();
     }
 
     /* ------------------------------------------------------------ */
     /* ------------------------------------------------------------ */
     /* ------------------------------------------------------------ */
     /* ------------------------------------------------------------ */
     /** Task.
      * The base class for scheduled timeouts.  This class should be
      * extended to implement the expire() method, which is called if the
      * timeout expires.
      * 
      * 
      *
      */
     public static class Task
     {
         Task _next;
         Task _prev;
         Timeout _timeout;
         long _delay;
         long _timestamp=0;
         boolean _expired=false;
 
         /* ------------------------------------------------------------ */
         protected Task()
         {
             _next=_prev=this;
         }
 
         /* ------------------------------------------------------------ */
         public long getTimestamp()
         {
             return _timestamp;
         }
 
         /* ------------------------------------------------------------ */
         public long getAge()
         {
             final Timeout t = _timeout;
             if (t!=null)
             {
                 final long now=t._now;
                 if (now!=0 && _timestamp!=0)
                     return now-_timestamp;
             }
             return 0;
         }
 
         /* ------------------------------------------------------------ */
         private void unlink()
         {
             _next._prev=_prev;
             _prev._next=_next;
             _next=_prev=this;
             _expired=false;
         }
 
         /* ------------------------------------------------------------ */
         private void link(Task task)
         {
             Task next_next = _next;
             _next._prev=task;
             _next=task;
             _next._next=next_next;
             _next._prev=this;   
         }
         
         /* ------------------------------------------------------------ */
         /** Schedule the task on the given timeout.
          * The task exiry will be called after the timeout duration.
          * @param timer
          */
         public void schedule(Timeout timer)
         {
             timer.schedule(this);
         }
         
         /* ------------------------------------------------------------ */
         /** Schedule the task on the given timeout.
          * The task exiry will be called after the timeout duration.
          * @param timer
          */
         public void schedule(Timeout timer, long delay)
         {
             timer.schedule(this,delay);
         }
         
         /* ------------------------------------------------------------ */
         /** Reschedule the task on the current timeout.
          * The task timeout is rescheduled as if it had been cancelled and
          * scheduled on the current timeout.
          */
         public void reschedule()
         {
             Timeout timeout = _timeout;
             if (timeout!=null)
                 timeout.schedule(this,_delay);
         }
         
         /* ------------------------------------------------------------ */
         /** Cancel the task.
          * Remove the task from the timeout.
          */
         public void cancel()
         {
             Timeout timeout = _timeout;
             if (timeout!=null)
             {
                 synchronized (timeout._lock)
                 {
                     unlink();
                     _timestamp=0;
                 }
             }
         }
         
         /* ------------------------------------------------------------ */
         public boolean isExpired() { return _expired; }
 
         /* ------------------------------------------------------------ */
 	public boolean isScheduled() { return _next!=this; }
         
         /* ------------------------------------------------------------ */
         /** Expire task.
          * This method is called when the timeout expires. It is called
          * in the scope of the synchronize block (on this) that sets 
          * the {@link #isExpired()} state to true.
          * @see #expired() For an unsynchronized callback.
          */
         protected void expire(){}
 
         /* ------------------------------------------------------------ */
         /** Expire task.
          * This method is called when the timeout expires. It is called 
          * outside of any synchronization scope and may be delayed. 
          * 
          */
         public void expired(){}
 
     }
 
 }