nixos-config/modules/system/services/syncthing/backups.nix

{
  config,
  pkgs,
  lib,
  ...
}:
let
  cfg = config.custom.services.syncthing;

  user = config.users.users.syncthing.name;
in
{
  options.custom.services.syncthing.backups.enable = lib.mkEnableOption "";

  config = lib.mkIf cfg.backups.enable {
    assertions = [
      {
        assertion = cfg.isServer;
        message = "syncthing backups can only be made on a server";
      }
    ];

    custom.services.resticBackups.syncthing = {
      inherit user;
      dependentService = "syncthing.service";
      extraConfig.paths = [ config.services.syncthing.dataDir ];
    };

    environment.systemPackages = [
      (pkgs.writeShellApplication {
        name = "syncthing-restore";
        text = ''
          sudo --user=${user} bash -c "
            systemctl stop syncthing.service
            restic-syncthing restore latest --target /
            systemctl start syncthing.service
          "
        '';
      })
    ];
  };
}