Offset a polycurve with a distance relative to an external boundary

Hi Grasshopper community!

I have been headbanging my head for a while now on this problem and I am running out of ideas.

I am trying to offset a polycurve (green) inwards relative to the distance measured to a boundary curve (black):

I am looking for the result below (blue curve):

I divide the green curve into the number of sides that the boundary has (4 in this case), so a segment of the green curve is offset according to the closest segment of the boundary curve(black). However, when I have done that, of course the curves are too long and they interesect each other and even some of them become redundant. See the image below:

Does anyone have a good suggestion how I can trim the redundant curves and redundant parts of the curves and get a closed offset polysurface (see 2nd image)?

Thanks!