make a text fit it's textbox with max font size without causing a text cropping

[md-ward]

I did an automation scripts using this api i was trying to make the text size as big as possible i was trying to get the textbox boundaries and make the text boundaries then increase the font size and update the text boundaries until it hit the textbox boundaries , the issues is with this api it returns box boundaries but it's wrong and cant tell what it is ,
does anyone know a way to make the text big as possible fitting the textbox without causing overflow cropping