Hey thanks Herb is best boi :)
In terms of the undo I save eat drawing circle in an array and that array gets redrawn each update. For each change to that array it is stored in an array of arrays so as you undo it just grabs the previous state. E.g
previous_drawings = [ [], [1], [1,2]]
current_drawings = [1,2,3]
undo
grab the last element of previous drawing -> current_drawings = [1,2]