create a milling toolpath

Hi guys!

I wonder if someone can help me out with this...

I need to create a toolpaht of a zig zag line (green line) inside a polyline (pink line) (like a hatch) that when hits the polyline border follows it down let's say for 5mm and then changes direction and goes back to the opposite way. Creating the zig zag line it's not a big problem but make it go down following the border and turning to the other side seems really tricky to me.

Any ideas?

Thanks!