using System;

namespace DistanceTask
{
    public static class DistanceTask
    {
        public static double K, M, Intersection_X, Intersection_Y;

        // Расстояние от точки (x, y) до отрезка AB с координатами A(ax, ay), B(bx, by)
        public static double GetDistanceToSegment(double ax, double ay, double bx, double by, double x, double y)
        {
            if (ax - bx != 0) return SegmentIsVertical(ref ax, ref ay, ref bx, ref by, ref x, ref y);
            else return SegmentIsNotVertical(ref ax, ref ay, ref bx, ref by, ref x, ref y);
        }

        public static double SegmentIsVertical(ref double ax, ref double ay,
                                               ref double bx, ref double by,
                                               ref double x, ref double y)
        {
            K = (ay - by) / (ax - bx);
            M = ay - K * ax;

            Intersection_Y = (M + K * K * y + K * x) / (1 + K * K);

            if (K != 0) Intersection_X = (Intersection_Y - M) / K;
            else Intersection_X = x;

            if ((x == ax && y == ay) ||
                 (x == bx && y == by) ||
                 (y == K * x + M && ((x >= ax && x <= bx) || (x >= bx && x <= ax))))
                return 0.0;
            else if ((Intersection_X >= ax && Intersection_X <= bx) ||
                     (Intersection_X <= ax && Intersection_X >= bx))
                return Math.Sqrt((x - Intersection_X) * (x - Intersection_X) +
                                  (y - Intersection_Y) * (y - Intersection_Y));
            return FindTheMinimumDistance(ref ax, ref ay, ref bx, ref by, ref x, ref y);
        }

        public static double SegmentIsNotVertical(ref double ax, ref double ay,
                                                  ref double bx, ref double by,
                                                  ref double x, ref double y)
        {
            Intersection_Y = y;
            Intersection_X = ax;

            if ((Intersection_Y >= ay && Intersection_Y <= by) ||
                 (Intersection_Y <= ay && Intersection_Y >= by))
                return Math.Sqrt((x - Intersection_X) * (x - Intersection_X) +
                                  (y - Intersection_Y) * (y - Intersection_Y));
            else if (x == ax && ((y >= ay && y <= by) ||
                    (y >= by && y <= ay)))
                return 0.0;
            return FindTheMinimumDistance(ref ax, ref ay, ref bx, ref by, ref x, ref y);
        }

        public static double FindTheMinimumDistance(ref double ax, ref double ay,
                                                    ref double bx, ref double by,
                                                    ref double x, ref double y)
        {
            return Math.Min(
                            Math.Sqrt( (x - ax) * (x - ax) + (y - ay) * (y - ay) ),
                            Math.Sqrt( (x - bx) * (x - bx) + (y - by) * (y - by) )
                           );
        }
    }
}