How to apply a dynamic theme manager system?

Question

Good time everyone. Is there any algorithms to implement a dynamic theme managing system which applies it just like Telegram & some ways to handle it from application layer (you suggest I should store it in database or save it by files or blob blob blob ... ). I'll be thank if you give me a basic sample or a short code (preferably in flutter:) )

I tried a database but there's many problems and difficulties to catch it and translate it for Material and change it into ThemeData ... even I can't talk about that. I tried files too & saved the destination theme file in cache directory but it had another difficulties ... !