using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace 测试Scottplot
{
    /***************************
    * Savitzky Golay filter 
    * E-Mail: w@sfox.cn
    ***************************/



    public class SavitzkyGolay
    {

        /// <summary>
        /// 滤波系数
        /// </summary>
        public double[] Coefficient { get; private set; }
        /// <summary>
        /// 构造梯度滤波器
        /// </summary>
        /// <param name="m">半步宽(m>0,m越大,平滑度越大)</param>
        public SavitzkyGolay(int m = 2)
        {
            this.SetCoefficient(m);
        }
        /// <summary>
        /// 设置滤波系数
        /// </summary>
        /// <param name="m">半步宽(m>0,m越大,平滑度越大)</param>
        public void SetCoefficient(int m)
        {
            List<double> result = new List<double>();
            int w = m * 2 + 1;
            double W2 = Math.Pow(w, 2);
            double a1 = 15 / (W2 - 4);
            double a2 = (W2 - 1) / 12;
            for (int j = -m; j <= m; j++)
            {
                result.Add((1 + a1 * (a2 - Math.Pow(j, 2))) / w);
            }
            //var ss = result.Select(x1 => x1.ToString()).Aggregate((a, b) => a + " " + b);
            this.Coefficient = result.ToArray();
        }

        /// <summary>
        /// 单点平滑
        /// </summary>
        /// <param name="list">平滑参考点(list.Length 必须等于 this.Coefficient.Length)</param>
        /// <returns></returns>
        public double Smooth(List<double> list)
        {
            double result = 0;
            for (int i = 0; i < this.Coefficient.Length; i++)
            {
                result += this.Coefficient[i] * list[i];
            }
            return result;
        }

        /// <summary>
        /// 曲线平滑
        /// </summary>
        /// <param name="curve">曲线</param>
        /// <returns></returns>
        public double[] Smoothes(double[] curve)
        {

            int length = curve.Length;
            double[] result = new double[length];//Result cache
            int k = this.Coefficient.Length / 2;
            //this.SetCoefficient(w);//Savitzky Golay Filter Coefficient
            Array.Copy(curve, result, k);//Fill head

            for (int i = k; i < length - k; i++)
            {
                List<double> list = new List<double>();//Smooth list
                for (int j = i - k; j <= i + k; j++)
                {
                    list.Add(curve[j]);
                }
                result[i] = this.Smooth(list);//Single point smooth
            }

            Array.Copy(curve, length - k, result, length - k, k);//Fill Tail
            return result;
        }
    }

}