Getting all permutations of Nested Spintax?

[noellarkin]

This snippet works perfectly for nested spintax:

However, I can't figure out how I can write a function that will output all the permutations of nested spintax.

For example: for a string "John went to the {{grocery |}store|library}" I would get:

John went to the library

John went to the store

John went to the grocery store

...

I can't figure this out - - I can kinda figure it out if there isn't any nesting (regex out all the text between brackets)...but nesting makes it pretty complicated for me to wrap my head around :)