using System;
using System.Collections.Generic;

namespace TMI_practicum
{
    public class Circle
    {
        public readonly double X;
        public readonly double Y;
        public readonly double R;

        public Circle(double x, double y, double r)
        {
            X = x;
            Y = y;
            R = r;
        }

        public double Distance(Circle otherCircle)
        {
            return Math.Round(Math.Sqrt(Math.Pow(X - otherCircle.X, 2) + Math.Pow(Y - otherCircle.Y, 2)), 15);
        }

        public IList<Intersection> FindIntersections(Circle c1)
        {
            var intersections = new List<Intersection>();
            double d = Distance(c1);
            if (d > R + c1.R || d < Math.Abs(R - c1.R) || d == 0.0 && R - c1.R == 0.0) return null;
            

            double a = Math.Round((R * R - c1.R * c1.R + d * d) / (2.0*d), 15);
            double px =  Math.Round(X + a * (c1.X - X) / d, 15);
            double py = Math.Round(Y + a * (c1.Y - Y) / d, 15);
            
            double htemp =  Math.Round(R * R - a * a, 15);
            if (htemp == 0)
            {
                intersections.Add(new Intersection(px, py));
            }
            else
            {
                double h = Math.Round(Math.Sqrt(htemp), 15);
                intersections.Add(new Intersection(px + h * (c1.Y - Y) / d, py - h * (c1.X - X) / d));
                intersections.Add(new Intersection(px - h * (c1.Y - Y) / d, py + h * (c1.X - X) / d));
            }

            return intersections;
        }
    }
}