/**
* A countdown timer with minutes and seconds.
* The timer does not go less than zero.
* @author Beth Katz
*/

public class Timer
{
   private static final int secInMin = 60;

   /**
      construct a timer with minutes and seconds of timer 
         (combined value should be positive)
      @param minutes number of minutes on newly constructed timer
      @param seconds number of seconds on newly constructed timer
   */
   public Timer(int minutes, int seconds)
   {
      set(minutes, seconds);
   }

   /**
      construct a timer with a positive number of minutes
      @param minutes number of minutes on newly constructed timer
   */
   public Timer(int minutes)
   {
      // alternatively could call     this(minutes, 0);
      // to call the two parameter constructor
      set(minutes, 0);
   }

   /**
      construct a timer with no initial value; timer set to zero
   */
   public Timer( )
   {
      set(0, 0);
   }

   /**
      sets minutes and seconds of timer (combined value should be positive)
      @param minutes number of minutes
      @param seconds number of seconds
   */
   public void set(int minutes, int seconds)
   {
      theSeconds = (minutes * secInMin) + seconds;
      if (theSeconds < 0) {
         System.err.println("Time must be non-negative." 
                             + " Timer set to zero");
         theSeconds = 0;
      }
   }

   /**
      sets minutes of timer (value should be positive)
      @param minutes number of minutes
   */
   public void set(int minutes)
   {
      set(minutes, 0);
   }

   /**
      sets timer to zero
   */
   public void set( )
   {
      set(0, 0);
   }

   /**
      builds a string of the timer's value in minutes:seconds form
      @return a string of the timer's value in minutes:seconds form
   */
   public String toString( )
   {
      int seconds = theSeconds % secInMin;
      String fill = seconds < 10 ? "0" : "";
      return (theSeconds/secInMin) + ":" + fill + seconds;
   }

   /**
      subtracts minutes and seconds from timer;
      timer should not fall below zero
      @param minutes number of minutes to subtract
      @param seconds number of seconds to subtract
   */
   public void subtract(int minutes, int seconds)
   {
      theSeconds -= (minutes * secInMin) + seconds;
      if (theSeconds < 0) {
         theSeconds = 0;
      }
   }

   /**
      returns whether timer has run out of time
      @return whether timer has run out of time 
   */
   public boolean outOfTime( )
   {
      return theSeconds == 0;
   }

   private int theSeconds; 
}