import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

/**
 * A timer which will correct itself since the javax.swing.Timer
 * is very inaccurate.
 */
public class TargetsTimer extends javax.swing.Timer {

   /*
    * The previous time that actionPerformed was called(in ms).
    */
   private long previousTime = 0;

   /*
    * The original value of the delay, since we call setDelay
    * multiple times and it modifies the other delay variable.
    */
   private int originalDelay;

   /*
    * Constructor.
    * @param delay the delay between time units
    * @param listener an actionlistener used to keep track of the time
    */
   public TargetsTimer(int delay,
         ActionListener listener) {
      super(delay, listener);
      originalDelay = delay;
   }

   /**
    * Override the fireActionPerformed method so we can
    * keep track of the previous time and determine how
    * inaccurate the update was.
    * @param e an ActionEvent
    */
   protected void fireActionPerformed(ActionEvent e) {
      super.fireActionPerformed(e);
      if (previousTime != 0) {
         int timeDifference =
            (int)((previousTime+super.getDelay())-System.currentTimeMillis());
         if ((originalDelay + timeDifference) > 0) {
            super.setDelay(originalDelay + timeDifference);
         }
      }
      previousTime = System.currentTimeMillis();
   }

   /*
    * Set the delay, reset originalDelay and previousTime variables.
    * @param delay the requested delay
    */
   public void setDelay(int delay) {
      super.setDelay(delay);
      originalDelay = delay;
      previousTime = 0;
   }

   /*
    * Stop and reset the previous time.
    */
   public void stop() {
      super.stop();
      previousTime = 0;
   }
}