using System;

namespace FftSharp.Windows
{
    public class Blackman : Window, IWindow
    {
        private readonly double A = 0.42659071;
        private readonly double B = 0.49656062;
        private readonly double C = 0.07684867;

        public override string Name => "Blackman";
        public override string Description =>
            "These exact values place zeros at the third and fourth sidelobes, " +
            "but result in a discontinuity at the edges and a 6 dB/oct fall-off. " +
            "The truncated coefficients do not null the sidelobes as well, but have an improved 18 dB/oct fall-off.";

        public Blackman() { }

        public Blackman(double a, double b, double c) : this()
        {
            (A, B, C) = (a, b, c);
        }

        protected override double windowValue(int index, int size)
        {
            return A - B * Math.Cos(2 * Math.PI * index / size) + C * Math.Cos(4 * Math.PI * index / size);
        }
    }
}