using System;

namespace KitsuneCafe.Event
{
  public sealed class ExponentialMovingAverage
  {
    private readonly float alpha;
    private float lastAverage = float.NaN;

    public ExponentialMovingAverage(int period)
    {
      if (period <= 0)
      {
        throw new ArgumentOutOfRangeException(nameof(period), "Period must be greater than 0.");
      }
      alpha = 2f / (period + 1);
    }

    public float NextValue(float value)
    {
      if (float.IsNaN(lastAverage))
      {
        lastAverage = value;
      }
      else
      {
        lastAverage = (value * alpha) + (lastAverage * (1 - alpha));
      }

      return lastAverage;
    }
  }
}