namespace Traffic_Light
{
    public partial class Form1 : Form
    {
        int state = 1;
        bool reverse = false;
        int borderSize = 10;

        public Form1()
        {
            InitializeComponent();
        }

        public void Switch()
        {
            if (state == 3) reverse = true;
            if (state == 1) reverse = false;

            if (reverse)
            {
                state--;
            }
            else
            {
                state++;
            }

            Invalidate();
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);

            Graphics g = e.Graphics;

            var brush = new SolidBrush(Color.Black);
            var pen = new Pen(Color.Black, borderSize);

            g.DrawRectangle(pen,
                50,
                50,
                50,
                150
            );

            brush.Color = Color.Gray;

            g.FillRectangle(brush,
                50,
                50,
                50,
                150
           );

            g.FillRectangle(brush, 50, 50, 50, 150);

            if (state == 1)
            {
                brush.Color = Color.Green;
                g.FillEllipse(brush, 50, 50, 50, 50);
                return;
            }
            if (state == 2)
            {
                brush.Color = Color.Yellow;
                g.FillEllipse(brush, 50, 100, 50, 50);
                return;
            }
            if (state == 3)
            {
                brush.Color = Color.Red;
                g.FillEllipse(brush, 50, 150, 50, 50);
                return;
            }
        }

        private void btn_switch_Click(object sender, EventArgs e)
        {
            Switch();
        }
    }
}