using System;
using System.Collections.Generic;

namespace Science.Mathematics.VectorCalculus
{
    public class LevelCurve
    {
        private Function.ToLastType<double, double, double> f;
        private double c;
        private Domain2D U;
        public LevelCurve(Function.ToLastType<double, double, double> function, double constant, Domain2D domain)
        {
            f = function;
            c = constant;
            U = domain;
        }
        public double Constant
        {
            set { c = value; }
        }

        private List<double> spx = new List<double>(1);
        public List<double> CurvePointX
        {
            get { return spx; }
        }
        private List<double> spy = new List<double>(1);
        public List<double> CurvePointY
        {
            get { return spy; }
        }

        public void FindCurve(double meshSize)
        {
            int nx = (int)((U.UpperBoundOfX - U.LowerBoundOfX) / meshSize);
            int ny = (int)((U.UpperBoundOfY - U.LowerBoundOfY) / meshSize);
            double x, y;
            double v1, v2, v3;
            for (int k = 0; k < nx - 1; k++)
            {
                for (int m = 0; m < ny - 1; m++)
                {
                    x = U.LowerBoundOfX + meshSize * k;
                    y = U.LowerBoundOfX + meshSize * m;
                    if (U.Check(x, y))
                    {
                        v1 = f(x, y) - c;
                        v2 = f(x + meshSize, y) - c;
                        v3 = f(x, y + meshSize) - c;
                        if (v1 * v2 <= 0.0)
                        {
                            spx.Add(x + meshSize * Math.Abs(v1) / (Math.Abs(v1) + Math.Abs(v2)));
                            spy.Add(y);
                        }
                        if (v1 * v3 <= 0.0)
                        {
                            spx.Add(x);
                            spy.Add(y + meshSize * Math.Abs(v1) / (Math.Abs(v1) + Math.Abs(v3)));
                        }
                    } 
                }
            }
        }
    }
}