nix-config/modules/darwin-modules/system.nix

{self, ...}: {
  system.configurationRevision = self.rev or self.dirtyRev or null;

  nix = {
    gc = {
      automatic = true;
      interval = [
        {
          Hour = 4;
          Minute = 15;
          Weekday = 7;
        }
      ];
      options = "--delete-older-than 7d";
    };
    optimise = {
      automatic = true;
      interval = [
        {
          Hour = 4;
          Minute = 15;
          Weekday = 7;
        }
      ];
    };
  };
}