namespace Yw.Curve
{
    /// <summary>
    /// 样条曲线（二次拟合）B=0
    /// </summary>
    public class TwinRelateCurve2B0 : IFitPoint
    {
        /// <summary>
        /// 
        /// </summary>
        public TwinRelateCurve2B0(CurveExpress express)
        {
            _express = express;
        }

        /// <summary>
        /// 
        /// </summary>
        public TwinRelateCurve2B0(List<CurvePoint> points)
        {
            if (points == null || points.Count < 3)
            {
                throw new Exception("出现数值计算问题, 无法解出二次拟合曲线(B=0)！");
            }
            _express = BuildCurveExpress(points);
        }

        //曲线表达式
        private CurveExpress _express = null;

        /// <summary>
        /// 获取拟合点Y
        /// </summary>
        public double GetFitPointY(double x)
        {
            if (_express == null)
            {
                return default;
            }
            return _express.Index2 * x * x + _express.Index0;
        }

        /// <summary>
        /// 获取拟合点列表
        /// </summary>
        public List<CurvePoint> GetFitPoints(int pointNumber)
        {
            if (_express == null)
            {
                return default;
            }
            return GetFitPointsByXRange(_express.Min, _express.Max, pointNumber);
        }

        /// <summary>
        /// 通过X区间获取拟合点列表
        /// </summary>
        public List<CurvePoint> GetFitPointsByXRange(double minX, double maxX, int pointNumber)
        {
            if (_express == null)
            {
                return default;
            }
            if (pointNumber < 1)
            {
                pointNumber = 12;
            }
            if (pointNumber > 10000)
            {
                pointNumber = 10000;
            }

            double space = (maxX - minX) / (pointNumber - 1);
            if (space < 0.0001)
            {
                return default;
            }
            var points = new List<CurvePoint>();
            for (int i = 0; i < pointNumber; i++)
            {
                double x = space * i + minX;
                double y = GetFitPointY(x);
                points.Add(new CurvePoint(x, y));
            }
            return points;
        }

        /// <summary>
        /// 创建曲线表达式
        /// </summary>
        public static CurveExpress BuildCurveExpress(List<CurvePoint> points)
        {
            if (points == null || points.Count < 3)
            {
                return default;
            }
            points = points.OrderBy(x => x.X).ToList();
            var count = points.Count;
            var express = new CurveExpress
            {
                FitType = eFitType.ConicCurveB0,
                DefinePoints = points.Select(x => new CurvePoint(x)).ToList(),
                Min = points.First().X,
                Max = points.Last().X
            };

            double rTotalH = 0.0;
            double rTotalHQ2 = 0.0;
            double rTotalQ2 = 0.0;
            double rTotalQ4 = 0.0;

            for (int i = 0; i < count; i++)
            {
                rTotalH = rTotalH + points[i].Y;
                rTotalHQ2 = rTotalHQ2 + points[i].Y * points[i].X * points[i].X;
                rTotalQ2 = rTotalQ2 + points[i].X * points[i].X;
                rTotalQ4 = rTotalQ4 + Math.Pow(points[i].X, 4);
            }
            express.Index2 = (rTotalH * rTotalQ2 - count * rTotalHQ2) / ((rTotalQ2 * rTotalQ2) - count * rTotalQ4);
            express.Index0 = (rTotalQ2 * rTotalHQ2 - rTotalQ4 * rTotalH) / ((rTotalQ2 * rTotalQ2) - count * rTotalQ4);

            return express;
        }



    }
}