using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace CircleGesture
{
    public partial class Form1 : Form
    {
        private List<Point> points;
        private bool capturing;
        private bool isCircle;
        private Point centroid;
        private double radius;

        private double Distance( Point a, Point b ) {
            return Math.Sqrt((b.X - a.X) * (b.X - a.X) + (b.Y - a.Y) * (b.Y - a.Y));
        }
        private bool isApproxCircle() {
            int k = points.Count;
            radius = 0;
            foreach (Point p in points)
                radius += Distance(centroid, p);
            radius /= k;

            const double eps = 0.35; // 35% difference to average is still ok.

            foreach (Point p in points)
            {
                double r = Distance(centroid, p);
                if (Math.Abs((radius-r)/radius)>eps)
                    return false;
            }
            return true;
        }

        public Form1()
        {
            InitializeComponent();
            points = new List<Point>();
        }

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            points.Clear();
            capturing = true;
            points.Add(e.Location);
            centroid.X = e.Location.X; centroid.Y = e.Location.Y;
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (capturing) {
                points.Add(e.Location);
                centroid.X += e.Location.X; centroid.Y += e.Location.Y;
            }
        }

        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            if (capturing) {
                points.Add(e.Location);
                centroid.X += e.Location.X; centroid.Y += e.Location.Y;
                centroid.X /= points.Count; centroid.Y /= points.Count;
                capturing = false;
                isCircle = isApproxCircle();
                Invalidate();
            }
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            System.Drawing.Graphics graphicsObj = this.CreateGraphics();
            Pen myPen = new Pen(System.Drawing.Color.Black, 2);
            int cnt = points.Count;
            if (cnt > 0)
            {
                Point[] pts = new Point[cnt];
                for (int i = 0; i < cnt; ++i)
                {
                    pts[i] = points[i];
                    graphicsObj.DrawLine(myPen, centroid, pts[i]);
                }
                graphicsObj.DrawPolygon(myPen, pts);
                if (isCircle)
                {
                    Int32 r = Convert.ToInt32(radius);
                    Rectangle myRectangle = new Rectangle(centroid.X - r, centroid.Y - r, 2*r, 2*r);
                    graphicsObj.DrawEllipse(myPen, myRectangle);
                }
            }
        }
    }
}