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 IEnumerable<Intersection> FindIntersections(Circle c1)
        {
            
            IList<Intersection> intersections;
            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 = (R * R - c1.R * c1.R + d * d) / (2.0*d);
            double px =  X + a * (c1.X - X) / d;
            double py = Y + a * (c1.Y - Y) / d;
            
            double htemp =  R * R - a * a;
            if (Math.Round(htemp, 15) == 0)
            {
                intersections = new Intersection[1];
                intersections[0] = new Intersection(Math.Round(px, 15), Math.Round(py, 15));
            }
            else
            {
                intersections = new Intersection[2];
                double h = Math.Sqrt(htemp);
                intersections[0] = new Intersection(Math.Round(px + h * (c1.Y - Y) / d, 15), Math.Round(py - h * (c1.X - X) / d, 15));
                intersections[1] = new Intersection(Math.Round(px - h * (c1.Y - Y) / d, 15), Math.Round(py + h * (c1.X - X) / d, 15));
            }

            return intersections;
        }
    }
}