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

namespace proj
{
    public partial class Form1 : Form
    {
        class Figure
        {
            public PointF p1;
            public float R;

            public Figure(PointF p1)
            {
                this.p1 = p1;
            }

        }

        private int mousestillclick = 0;
        private bool initialized = false;
        private List<Figure> figures = new List<Figure>();
        private int figurescount = 0;
        private PointF mousea;
        private PointF start;
        private PointF[] MaxChord = new PointF[2];
        private double MaxChordLength = 0;
        Pen pen = new Pen(Color.Red);

        public Form1() { InitializeComponent(); }

        private void Form1_MouseDown(object sender, MouseEventArgs e) {
            initialized = true;
            start = new PointF(e.X, e.Y);
            mousestillclick = 1;
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e) {
            mousea = new PointF(e.X, e.Y);
            if (mousestillclick == 1) Refresh();
        }

        private void Form1_MouseUp(object sender, MouseEventArgs e) {
            mousestillclick = 0; Refresh();
        }

        private void Form1_Paint_1(object sender, PaintEventArgs e) {
            if (!initialized) return;
            Font font = new Font("Times New Roman", 14);
            Brush brush = new SolidBrush(Color.Black);

            if (mousestillclick == 1)
            {
                float sq1 = (mousea.X - start.X) * (mousea.X - start.X) + (mousea.Y - start.Y) * (mousea.Y - start.Y);
                e.Graphics.DrawEllipse(pen, start.X - (float)Math.Sqrt(sq1), start.Y - (float)Math.Sqrt(sq1),
                    2 * (float)Math.Sqrt(sq1), 2 * (float)Math.Sqrt(sq1));

                if (figurescount != 0)
                    for (int i = 0; i < figurescount; i++)
                        e.Graphics.DrawEllipse(pen, figures[i].p1.X - figures[i].R, figures[i].p1.Y - figures[i].R,
                            2 * figures[i].R, 2 * figures[i].R);
            }
            else
            {
                float sq1 = (mousea.X - start.X) * (mousea.X - start.X) + (mousea.Y - start.Y) * (mousea.Y - start.Y);
                figures.Add(new Figure(new PointF(start.X, start.Y)));
                figurescount++;
                figures[figurescount - 1].R = (float)Math.Sqrt(sq1);

                if (figurescount != 0)
                    for (int i = 0; i < figurescount; i++)
                    {
                        e.Graphics.DrawEllipse(pen, figures[i].p1.X - figures[i].R, figures[i].p1.Y - figures[i].R,
                            2 * figures[i].R, 2 * figures[i].R);


                        for (int j = 0; j < figurescount; j++)
                        {
                            if (j == i) continue;
                            float x1 = figures[i].p1.X;
                            float x2 = figures[j].p1.X;
                            float y1 = figures[i].p1.Y;
                            float y2 = figures[j].p1.Y;
                            float dis = (float)Math.Sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
                            float R0 = figures[i].R;
                            float R1 = figures[j].R;



                            if ((dis > R0 + R1) || (dis < Math.Abs(R0 - R1)))
                                continue;

                            float a = (R0 * R0 - R1 * R1 + dis * dis) / (2 * dis);
                            float h = (float)Math.Sqrt(R0 * R0 - a * a);

                            float P2x = x1 + (a * (x2 - x1) / dis);
                            float P2y = y1 + (a * (y2 - y1) / dis);

                            float IP1x = P2x + (h * (y2 - y1) / dis);
                            float IP2x = P2x - (h * (y2 - y1) / dis);
                            float IP1y = P2y - (h * (x2 - x1) / dis);
                            float IP2y = P2y + (h * (x2 - x1) / dis);


                            float chordlength = (float)Math.Sqrt((IP2x - IP1x) * (IP2x - IP1x) + (IP2y - IP1y) * (IP2y - IP1y));
                            if (chordlength > MaxChordLength)
                            {
                                MaxChordLength = chordlength;
                                MaxChord[0].X = IP1x; MaxChord[1].X = IP2x;
                                MaxChord[0].Y = IP1y; MaxChord[1].Y = IP2y;
                            }
                        }
                    }
            }

            string maxrest = "Max = " + MaxChordLength;
            e.Graphics.DrawString(maxrest, font, brush, 600, 70);
            e.Graphics.DrawLine(new Pen(Color.Blue), MaxChord[0],MaxChord[1]);
        }
    }
}