using System;
using System.Collections.Generic;

namespace TMI_practicum
{
    public static class SimpleAlgorithm
    {
        public static IEnumerable<Intersection> Solve(IList<Circle> circles)
        {
            var intersections = new Stack<Intersection>();

            for (int i = 0; i < circles.Count - 1; i++)
            {
                for (int j = i + 1; j < circles.Count; j++)
                {
                    var c1 = circles[i];
                    var c2 = circles[j];
                    CalculateIntersection(intersections, c1, c2);
                }
            }

            return intersections;
        }

        private static void CalculateIntersection(Stack<Intersection> intersections, Circle c1, Circle c2)
        {
            double d = c1.Distance(c2);
            if (d > c1.R + c2.R || d < Math.Abs(c1.R - c2.R)) return;

            if (d == 0.0 && c1.R - c2.R == 0.0) throw new ArgumentException("Circles may not be coincident!");
            
            double a = (c1.R * c1.R - c2.R * c2.R + d * d) / (2.0*d);
            double px = c1.X + a * (c2.X - c1.X) / d;
            double py = c1.Y + a * (c2.Y - c1.Y) / d;

            double htemp = c1.R * c1.R - a * a;
            if (htemp == 0)
            {
                intersections.Push(new Intersection(px, py));
            }
            else
            {
                double h = Math.Sqrt(htemp);
                intersections.Push(new Intersection(px + h * (c2.Y - c1.Y) / d, py - h * (c2.X - c1.X) / d));
                intersections.Push(new Intersection(px - h * (c2.Y - c1.Y) / d, py + h * (c2.X - c1.X) / d));
            }
        }
    }
}