MainForm.cs

public partial class MainForm : Form 
{
    // Code omitted for brevity
    
    // The history list
    private Stack<ICommand> _commands = new Stack<ICommand>();
    
    // Code omitted for brevity
    
    // Draws the shape on canvas
    private void canvas_MouseDown(object sender, MouseEventArgs e)
    {
      // We get the command based on the shape selection
      // and we draw it in the X, Y coordinates
      var command = GetCommand(e.X, e.Y);
      command.Draw();

      // We store the command in the history list
      _commands.Push(command);
      
      // Refresh the UI (trivial code, omitted for brevity)
      RefreshWindow();
    }
}