{ pkgs, lib, config, ... }:

{
  options.tailscalePreAuth = lib.mkOption {
    type = lib.types.str;
  };
  options.tailscaleAdvertiseRoutes = lib.mkOption {
    type = lib.types.str;
    default = "";
  };

  # make the tailscale command usable to users
  config.environment.systemPackages = [ pkgs.tailscale ];

  # enable the tailscale service
  config.services.tailscale.enable = true;

  config.systemd.services.tailscale-autoconnect = {
    description = "Automatic connection to Tailscale";

    # make sure tailscale is running before trying to connect to tailscale
    after = [ "network-pre.target" "tailscale.service" ];
    wants = [ "network-pre.target" "tailscale.service" ];
    wantedBy = [ "multi-user.target" ];

    # set this service as a oneshot job
    serviceConfig.Type = "oneshot";

    # have the job run this shell script
    script = with pkgs; ''
      # wait for tailscaled to settle
      sleep 2

      # check if we are already authenticated to tailscale
      status="$(${tailscale}/bin/tailscale status -json | ${jq}/bin/jq -r .BackendState)"
      if [ $status = "Running" ]; then # if so, then do nothing
        exit 0
      fi

      # otherwise authenticate with tailscale
      ${tailscale}/bin/tailscale up \
        --authkey "$(<${config.tailscalePreAuth})" \
        --advertise-routes "${config.tailscaleAdvertiseRoutes}"
    '';
  };
}