TMA Band v2

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

namespace cAlgo
{
    [Indicator(IsOverlay = true, TimeZone = TimeZones.UTC, AccessRights = AccessRights.None)]
    public class TMABandsv2 : Indicator
    {
        [Parameter(DefaultValue = 60, MinValue = 1)]
        public int HalfLength { get; set; }

        [Parameter()]
        public DataSeries Price { get; set; }

        [Parameter(DefaultValue = 2.5)]
        public double ATRMultiplier { get; set; }

        [Parameter(DefaultValue = 100)]
        public int ATRPeriod { get; set; }

        [Output("Center", LineColor = "red", PlotType = PlotType.Points)]
        public IndicatorDataSeries Center { get; set; }

        [Output("Upper", LineColor = "blue")]
        public IndicatorDataSeries Upper { get; set; }

        [Output("Lower", LineColor = "blue")]
        public IndicatorDataSeries Lower { get; set; }

        private AverageTrueRange _atr;

        private bool previousClosesAbove;
        private bool previousClosesBelow;
        private int arrowLastCalculated;

        protected override void Initialize()
        {
            _atr = Indicators.AverageTrueRange(ATRPeriod, MovingAverageType.Simple);
        }

        public override void Calculate(int index)
        {
            if (index < HalfLength)
                return;
            double sum = (HalfLength + 1) * Price[index];
            double sumw = (HalfLength + 1);

            for (int j = 1, k = HalfLength; j <= HalfLength; j++,k--)
            {
                sum += k * Price[index - j];
                sumw += k;
            }

            double range = _atr.Result[index - 10] * ATRMultiplier;

            Center[index] = sum / sumw;
            Upper[index] = Center[index] + range;
            Lower[index] = Center[index] - range;

            paintArrows(index);
        }

        private void paintArrows(int index)
        {
            if (arrowLastCalculated == index || index == 0)
            {
                return;
            }
            arrowLastCalculated = index;
            previousClosesAbove = Bars[index - 2].Close > Upper[index - 2];
            previousClosesBelow = Bars[index - 2].Close < Lower[index - 2];
            if (previousClosesAbove && Bars[index - 1].Close < Upper[index - 1])
            {
                Chart.DrawIcon(index + "AD", ChartIconType.DownArrow, Bars[index - 1].OpenTime, Math.Max(Bars[index - 2].High, Bars[index - 1].High), Color.Yellow);
            }
            if (previousClosesBelow && Bars[index - 1].Close > Lower[index - 1])
            {
                Chart.DrawIcon(index + "AU", ChartIconType.UpArrow, Bars[index - 1].OpenTime, Math.Min(Bars[index - 2].Low, Bars[index - 1].Low), Color.LightBlue);
            }
        }
    }
}