Create algorhitm to create .pak file from unpack code

Question

i'm trying to write a code to create .pak file from file list in dart. I have already the code for extract entries from .pak file (it use lz4 for compression) but i'm trying to make the reverse thing. Someone can help me to achieve this? I'm not really skilled on manage byte array of data

create a .pak file with lz4 compression from a list of file

there is the code for decompress

https://gist.github.com/riccardo-runci/faba3d03e0b64fffb8ca873dcbbf2bf6

Thanks!

UPDATE: i have write something like this, it generate the .pak file but if i try to uncompress it back i get invalid signature for header

https://gist.github.com/riccardo-runci/a2f91fa1d39d09d03d7ef17e40b3e1ff