namespace I3.Clocks
{
	public class Clock 
	{
		public const int HoursPerDay = 24;
		public const int MinutesPerHour = 60;
			
		protected int hour, 
					  minute;
			
		public int Hour
		{
			get {return hour;}
		}

		public int Minute
		{
			get {return minute;}
		}
			
		public static bool IsValidTime (int hour, int minute)
		{
			return
				0 <= hour && hour < HoursPerDay &&
				0 <= minute && minute < MinutesPerHour;
		}
			
		[System.Diagnostics.Conditional("DEBUG")]		// braucht man das?
		public virtual void Set (int hour, int minute)
		{
			System.Diagnostics.Debug.Assert(IsValidTime(hour, minute), "precondition");
			this.hour	= hour;
			this.minute	= minute;
			System.Diagnostics.Debug.Assert(IsValidTime(this.hour, this.minute), "invariant");
		}

		[System.Diagnostics.Conditional("DEBUG")]		// braucht man das?  
		public virtual void Tick ()
		{
			System.Diagnostics.Debug.Assert(IsValidTime(hour, minute), "invariant");
			minute = (minute + 1) % MinutesPerHour;
			if (minute == 0)
			{
				hour = (hour + 1) % HoursPerDay;
			}
			System.Diagnostics.Debug.Assert(IsValidTime(hour, minute), "invariant");
		}
	} // end of Clock
}