home-manager/modules/lib/strings.nix

{ lib }:

let
  inherit (lib)
    genList length lowerChars replaceStrings stringToCharacters upperChars;
in {
  # Figures out a valid Nix store name for the given path.
  storeFileName = path:
    let
      # All characters that are considered safe. Note "-" is not
      # included to avoid "-" followed by digit being interpreted as a
      # version.
      safeChars = [ "+" "." "_" "?" "=" ] ++ lowerChars ++ upperChars
        ++ stringToCharacters "0123456789";

      empties = l: genList (x: "") (length l);

      unsafeInName =
        stringToCharacters (replaceStrings safeChars (empties safeChars) path);

      safeName = replaceStrings unsafeInName (empties unsafeInName) path;
    in "hm_" + safeName;
}