Pure-FTPd with uploadscript on NixOS

ftp-uploadscript.sh

#!/run/current-system/sw/bin/bash

SCANNED="$1"
AFFIX="${1##*.}"
DATESTAMP=$(date '+%Y%m%d')
TIMESTAMP=$(date '+%H%M%S')

mv "${SCANNED}" "/home/user/${DATESTAMP}..scan-${TIMESTAMP}.${AFFIX}"

pure-ftpd.nix

{ config, pkgs, ... }:

let uploadScript = "/etc/nixos/pkgs/pure-ftpd/ftp-uploadscript.sh";

in {

  nixpkgs.config.packageOverrides = pkgs:
    { pure-ftpd = pkgs.pure-ftpd.overrideAttrs (oldAttrs: {
        configureFlags = [ "--with-uploadscript" ];});
    };

  users.groups.ftp.gid = config.ids.gids.ftp;
  users.users.ftp = {
    uid = config.ids.uids.ftp;
    group = "ftp";
    description = "Anonymous FTP user";
    home = "/home/ftp";
  };
  users.users.scr.extraGroups = [ "ftp" ];

  systemd.services.pure-ftpd = {
    description = "Pure-FTPd Server";
    wantedBy = [ "multi-user.target" ];
    after = [ "network.target" ];
    serviceConfig.ExecStart = "${pkgs.pure-ftpd}/bin/pure-ftpd --daemonize --anonymousonly --anonymouscancreatedirs --uploadscript --passiveportrange 30000:50000";
    serviceConfig.Type = "forking";
    serviceConfig.Restart = "always";
  };

  systemd.services.pure-uploadscript = {
    description = "Pure-FTPd helper";
    wantedBy = [ "multi-user.target" ];
    requires = [ "pure-ftpd.service" ];
    after = [ "pure-ftpd.service" ];
    serviceConfig.ConditionPathExists = uploadScript;
    serviceConfig.ExecStart = "${pkgs.pure-ftpd}/bin/pure-uploadscript -B -r ${uploadScript}";
    serviceConfig.Type = "forking";
    serviceConfig.Restart = "always";
  };

  networking.firewall.allowedTCPPortRanges = [ { from = 30000; to = 50000; } ];
  networking.firewall.allowedUDPPortRanges = [ { from = 30000; to = 50000; } ];
  networking.firewall.allowedTCPPorts = [ 21 ];
  networking.firewall.allowedUDPPorts = [ 21 ];

}