using System;

namespace Science.Mathematics.VectorCalculus
{
    public class TangentPlaneOfGraph
    {
        private Function.ToLastType<double, double, double> func;
        public TangentPlaneOfGraph(Function.ToLastType<double,double,double> f, Point p)
        {
            func = f;
            pp = p;
        }
        public void Compute()
        {
            double[] at = {pp.Coordinate[0], pp.Coordinate[1]};
            Function.ToLastType<double[], double> fv
                = new Function.ToLastType<double[], double>(ff);
            PartialDerivative obj = new PartialDerivative(fv, at);
            obj.WithRespectTo = 0;
            obj.Compute();
            cx = obj.Result;
            obj.WithRespectTo = 1;
            obj.Compute();
            cy = obj.Result;
            c = -cx * at[0] - cy * at[1] + func(at[0],at[1]);
        }
        private Point pp;
        public Point At
        {
            set { pp = value; }
        }
        private double cx, cy, c;
        public double CoefficientOfX
        {
            get { return cx; }
        }
        public double CoefficientOfY
        {
            get { return cy; }
        }
        public double Constant
        {
            get { return c; }
        }
        private double ff(double[] xv)
        {
            double x = xv[0];
            double y = xv[1];
            return func(x, y);
        }
    }
}