Timer.cs

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namespace StateMachine
{
    public struct Timer<TS>
    {
        public double Value { get; set; }
        public TimeUnit Unit { get; set; }
        public double Time { get; set; }
        public TS Target { get; set; }

        public Timer(TS target, double value, TimeUnit unit)
        {
            Target = target;
            Value = value;
            Unit = unit;
            Time = 0;
            Reset();
        }

        public void Reset()
        {
            Time = Value * (long) Unit;
        }

        /// <summary>
        ///     Lets the specified time tick away and subtracts it from the Timer.<br />
        ///     If the timer triggered the time that was left after the Timer triggered is returned.
        /// </summary>
        /// <param name="timeInMillis">The time to tick away.</param>
        /// <returns>Null if the timer didn't trigger, a positive value otherwise.</returns>
        public double? Tick(double timeInMillis)
        {
            Time -= timeInMillis;
			if (!(Time <= 0D)) return null;

			var d = Time * -1D;
			Reset();
			return d;
		}
    }
}