John Ehlers Trendflex indicator

using System;
using cAlgo.API;
using cAlgo.API.Indicators;
using cAlgo.API.Internals;

namespace cAlgo
{
    [Levels(0)]
    [Indicator(IsOverlay = false, TimeZone = TimeZones.UTC, AccessRights = AccessRights.None)]
    public class mEhlersTrendflex : Indicator
    {
        [Parameter("Period (20)", DefaultValue = 20)]
        public int inpPeriod { get; set; }
        [Parameter("Data Source (close)", DefaultValue = enumPriceTypes.Close)]
        public enumPriceTypes inpPriceType { get; set; }  

        [Output("TrendFlex", LineColor = "Black", PlotType = PlotType.Line, LineStyle = LineStyle.Solid, Thickness = 1)]
        public IndicatorDataSeries outTrendflex { get; set; }
        
        private double _a1, _b1, _c1, _c2, _c3;
        private IndicatorDataSeries _price, _filt, _sum, _raw, _ms, _trendflex;

        protected override void Initialize()
        {
            _a1 = Math.Exp(-1.414 * 3.14159 / (0.5 * inpPeriod));
            _b1 = 2 * _a1 * Math.Cos(1.414 * 180 / (0.5 * inpPeriod));
            _c3 = -_a1 * _a1 ;
            _c2 = _b1 ;
            _c1 = 1 - _c2 - _c3 ;
            _price = CreateDataSeries();
            _filt = CreateDataSeries();
            _sum = CreateDataSeries();
            _raw = CreateDataSeries();
            _ms = CreateDataSeries();
            _trendflex = CreateDataSeries();
        }

        public override void Calculate(int i)
        {
            switch(inpPriceType)
            {
                case enumPriceTypes.Open:
                    _price[i] = Bars.OpenPrices[i];
                    break;
                case enumPriceTypes.Close:
                    _price[i] = Bars.ClosePrices[i];
                    break;
                case enumPriceTypes.High:
                    _price[i] = Bars.HighPrices[i];
                    break;
                case enumPriceTypes.Low:
                    _price[i] = Bars.LowPrices[i];
                    break;
                case enumPriceTypes.Median:
                    _price[i] = Bars.MedianPrices[i];
                    break;
                case enumPriceTypes.Typical:
                    _price[i] = Bars.TypicalPrices[i];
                    break;
                case enumPriceTypes.Weighted:
                    _price[i] = Bars.WeightedPrices[i];
                    break;
                default:
                    _price[i] = Bars.ClosePrices[i];
                    break;
            }
            
            _filt[i] = _c1 * (_price[i] + _price[i-1]) / 2 + _c2 * (i>1 ? _filt[i-1] : 0) + _c3 * (i>2 ? _filt[i-2] : 0);
            _sum[i] = 0;
            for (int j=1; j<inpPeriod; j++)
                _sum[i] += _filt[i] - (i>inpPeriod ? _filt[i-j] : 0);
            _raw[i] = _sum[i] / inpPeriod;
            _ms[i] = 0.04 * _raw[i] * _raw[i] + (i>1 ? 0.96 * (!double.IsNaN(_ms[i-1]) ? _ms[i-1] : 1) : 0);
            _trendflex[i] = _ms[i] != 0 ? _raw[i] / Math.Sqrt(_ms[i]) : 0;

            outTrendflex[i] = _trendflex[i];
        }
    }
    
    public enum enumPriceTypes
    {
        Open,
        Close,
        High,
        Low,
        Median,
        Typical,
        Weighted
    }
}