using System;
using System.ComponentModel;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace Ellipse_Control
{
    internal class EllipseTool : Component
    {
        [DllImport("Gdi32.dll", SetLastError = true)]
        private static extern IntPtr CreateRoundRectRgn(
    int nLeftRect,
    int nTopRect,
    int nRightRect,
    int nBottomRect,
    int nWidthEllipse,
    int nHeightEllipse);

        private Control _targetControl;
        private int _cornerRadius = 30;
        private readonly EventHandler _sizeChangedHandler;

        public EllipseTool()
        {
            _sizeChangedHandler = new EventHandler(OnControlSizeChanged);
        }

        [Category("Appearance")]
        public Control TargetControl
        {
            get => _targetControl;
            set
            {
                if (_targetControl != null)
                {
                    _targetControl.SizeChanged -= _sizeChangedHandler;
                }
                _targetControl = value;
                if (_targetControl != null)
                {
                    _targetControl.SizeChanged += _sizeChangedHandler;
                    UpdateRegion();
                }
            }
        }
        [Category("Appearance")]
        public int CornerRadius
        {
            get => _cornerRadius;
            set
            {
                _cornerRadius = value;
                UpdateRegion();
            }
        }

        private void OnControlSizeChanged(object sender, EventArgs e)
        {
            UpdateRegion();
        }

        private void UpdateRegion()
        {
            if (_targetControl == null || _targetControl.IsDisposed) return;

            IntPtr regionHandle = CreateRoundRectRgn(
                0, 0,
                _targetControl.Width + 1,
                _targetControl.Height + 1,
                _cornerRadius,
                _cornerRadius);
            _targetControl.Region = Region.FromHrgn(regionHandle);
        }
    }
}