/** A class that extends the Server class
    Is a server that also has a queue attached to it
    @author Erika Harrison
    @version 1.0 24-06-02
*/
public class QueuedServer extends Server
{  private Queue queue = DataFactory.makeQueue();

   //instance variables used for statistics
   private double totalQueueTime = 0;
   private double queueLengthTime = 0;
   private double busyTime = 0;
   private double lastChangeInQueue = 0;

   private boolean recordStats = false;

   //creates the server
   public QueuedServer()
   {  super();
   }

   public void addEvent(Student student, double currTime)
   //pre: student != null
   //post: adds another event to the server given the server's current situation
   //   ie. adds to the queue if there is currently a student, or sets up the next
   //   event if there is no current student
   {  if (getStudent() == null)  //there is no current student being processed
      {  //sets up the new student to be processed
         setStudent(student);

         //increments the server stats as necessary
         double meanTime = generateNextTime.nextExp(mean);
         setTime(meanTime + currTime);

         if (recordStats)
         {  busyTime += meanTime;
         }
      }else  //the server is currently busy
      {
         if (recordStats)
         {  totalQueueTime += (currTime - lastChangeInQueue) * queue.size();
         }
         Debug.println("Time Change = " + (currTime - lastChangeInQueue) + " Queue Size " + queue.size());

         lastChangeInQueue = currTime;

         queue.enqueue(student);

         //required to update the student's queue time stats
         student.addToQueue(currTime);
      }
   }

   public void setNextEvent(double currTime)
   //pre: the previous student is finished processing
   //post: a new event is set up, if it exists (if there are students waiting
   //   in the queue
   {  if (queue.size() != 0)  //students exist in the queue
      {
         //increments the server stats as necessary
         double nextTime = generateNextTime.nextExp(mean);
         setTime(nextTime + currTime);

         if (recordStats) 
         {  totalQueueTime += (currTime - lastChangeInQueue) * queue.size(); 
            busyTime += nextTime;
         }
         Debug.println("Time Change = " + (currTime - lastChangeInQueue) + " Queue Size " + queue.size());

         lastChangeInQueue = currTime;

         //starts processing a new student
         Student student = (Student)queue.dequeue();
         setStudent(student);

         //required to update the student's queue time stats
         student.doneQueue(currTime);

      }
   }

   public int getQueueLength()
   //pre: true
   //post: returns the number of students in the server's queue
   {  return queue.size();
   }

   public double getQueueTime()
   //pre: true
   //post: returns the current amount of time spent by each processed student
   //   in the server
   {  return totalQueueTime;
   }

   public double getBusyTime()
   //pre: true
   //post: returns the current amount of time spent processing the already
   //   processed students
   {  return busyTime;
   }

   public void startStats()
   //pre: true
   //post: the stats of the server are initialized
   {  recordStats = true;
   }

}