Decompress File Paths in Scala

A comma separated list of strings can be compressed by finding common substrings and grouping those strings together into Token Lists

More formally, a Token List is a list where each item can be one of the following:

• a string
• a concatenation of Token Lists

Examples:

ab,ac => a{b,c}
ac,ad,bc,bd => {a,b}{c,d}
axc,axd,bxc,bxd => {a,b}x{c,d}

This technique is used to compress folder paths since a folder like

README.md
resources/
    js/
        app.js
        boot.js
        comp/
            a.js
            b.js

can be represented as a list of strings:

[
    "README.md",
    "resources/js/app.js",
    "resources/js/boot.js",
    "resources/js/comp/a.js",
    "resources/js/comp/b.js"
]

and further encoded into comma separated string

“README.md,resources/js/app.js,resources/js/boot.js,resources/js/comp/a.js,resources/js/comp/b.js”

and then we can compress them to the following Token List:

README.md,resources/js/{app,boot,comp/{a,b}}.js

Given a Token List representing a compressed folder, return the initial list of paths.

Example 1:

Input:
"resources/{js/{app.js,comp/{a.js,b.js},boot.js}},README.md"

Output: [
    "README.md",
    "resources/js/app.js",
    "resources/js/boot.js",
    "resources/js/comp/a.js",
    "resources/js/comp/b.js"
]

Example 2:

Input:
"my_{first,second}_folder/{a,b}{.js,.py}"

Output: [
    "my_first_folder/a.js,
    "my_first_folder/a.py,
    "my_first_folder/b.js,
    "my_first_folder/b.py,
    "my_second_folder/a.js,
    "my_second_folder/a.py,
    "my_second_folder/b.js,
    "my_second_folder/b.py
]

Note: The resulting array can be in any order