Gets the rectangle of the caret in the TextBox

TextBoxExtensions.cs

using Microsoft.UI.Xaml.Controls;
using Windows.Foundation;

namespace OaktreeLab.Utils.WinUI3 {
    /// <summary>
    /// Class that provides extension methods for TextBox.
    /// </summary>
    public static class TextBoxExtensions {
        /// <summary>
        /// Gets the rectangle of the caret in the TextBox.
        /// </summary>
        /// <remarks>
        /// The width of the rectangle is always zero.
        /// If the text is empty, the returned rectangle is at the origin (0, 0) with zero width and height.
        /// </remarks>
        /// <returns>The caret's Rect</returns>
        public static Rect GetCaretRect( this TextBox textBox ) {
            int caretIndex = textBox.SelectionStart;
            string text = textBox.Text;

            Rect caretRect;
            if ( text.Length == 0 ) {
                // If the text is empty, return a rectangle at the origin
                caretRect = new Rect( 0, 0, 0, 0 );
            } else if ( caretIndex == text.Length ) {
                // If the caret is at the end of the text
                if ( text[ text.Length - 1 ] == '\r' ) {
                    // If the caret is immediately after a newline character, calculate the start position of the next line based on the previous character's rectangle
                    caretRect = textBox.GetRectFromCharacterIndex( caretIndex - 1, true );
                    caretRect.X = textBox.GetRectFromCharacterIndex( 0, false ).X;
                    caretRect.Y += caretRect.Height;
                } else {
                    // If the caret is at the end of the text and not after a newline character, get the rectangle of the last character
                    caretRect = textBox.GetRectFromCharacterIndex( caretIndex - 1, true );
                }
            } else {
                // If the caret is in the middle of the text, get the rectangle at the caret position
                caretRect = textBox.GetRectFromCharacterIndex( caretIndex, false );
            }

            return caretRect;
        }
    }
}