os/modules/ddclient/default.nix

{
  config,
  pkgs,
  lib,
  ...
}: let
  cfg = config.services.ddclient;
  boolToStr = bool:
    if bool
    then "yes"
    else "no";
  dataDir = "/var/lib/ddclient";
  StateDirectory = builtins.baseNameOf dataDir;
  RuntimeDirectory = StateDirectory;

  usev4 =
    if cfg.usev4 != ""
    then "usev4=${cfg.usev4}"
    else "";
  usev6 =
    if cfg.usev6 != ""
    then "usev6=${cfg.usev6}"
    else "";

  configFile' = pkgs.writeText "ddclient.conf" ''
    # This file can be used as a template for configFile or is automatically generated by Nix options.
    use=no
    ${usev4}
    ${usev6}
    cache=${dataDir}/ddclient.cache
    foreground=yes
    login=${cfg.username}
    password=${
      if cfg.protocol == "nsupdate"
      then "/run/${RuntimeDirectory}/ddclient.key"
      else "@password_placeholder@"
    }
    protocol=${cfg.protocol}
    ${lib.optionalString (cfg.script != "") "script=${cfg.script}"}
    ${lib.optionalString (cfg.server != "") "server=${cfg.server}"}
    ${lib.optionalString (cfg.zone != "") "zone=${cfg.zone}"}
    ssl=${boolToStr cfg.ssl}
    wildcard=yes
    quiet=${boolToStr cfg.quiet}
    verbose=${boolToStr cfg.verbose}
    ${cfg.extraConfig}
    ${lib.concatStringsSep "," cfg.domains}
  '';
  configFile =
    if (cfg.configFile != null)
    then cfg.configFile
    else configFile';

  preStart = ''
    install --mode=600 --owner=$USER ${configFile} /run/${RuntimeDirectory}/ddclient.conf
    ${lib.optionalString (cfg.configFile == null) (
      if (cfg.protocol == "nsupdate")
      then ''
        install --mode=600 --owner=$USER ${cfg.passwordFile} /run/${RuntimeDirectory}/ddclient.key
      ''
      else if (cfg.passwordFile != null)
      then ''
        "${pkgs.replace-secret}/bin/replace-secret" "@password_placeholder@" "${cfg.passwordFile}" "/run/${RuntimeDirectory}/ddclient.conf"
      ''
      else ''
        sed -i '/^password=@password_placeholder@$/d' /run/${RuntimeDirectory}/ddclient.conf
      ''
    )}
  '';
in
  with lib; {
    disabledModules = [
      "services/networking/ddclient.nix"
    ];

    imports = [
      (mkChangedOptionModule ["services" "ddclient" "domain"] ["services" "ddclient" "domains"]
        (config: let
          value = getAttrFromPath ["services" "ddclient" "domain"] config;
        in
          if value != ""
          then [value]
          else []))
      (mkRemovedOptionModule ["services" "ddclient" "homeDir"] "")
      (mkRemovedOptionModule ["services" "ddclient" "password"] "Use services.ddclient.passwordFile instead.")
    ];

    ###### interface

    options = {
      services.ddclient = with lib.types; {
        enable = mkOption {
          default = false;
          type = bool;
          description = lib.mdDoc ''
            Whether to synchronise your machine's IP address with a dynamic DNS provider (e.g. dyndns.org).
          '';
        };

        package = mkOption {
          type = package;
          default = pkgs.ddclient;
          defaultText = lib.literalExpression "pkgs.ddclient";
          description = lib.mdDoc ''
            The ddclient executable package run by the service.
          '';
        };

        domains = mkOption {
          default = [""];
          type = listOf str;
          description = lib.mdDoc ''
            Domain name(s) to synchronize.
          '';
        };

        username = mkOption {
          # For `nsupdate` username contains the path to the nsupdate executable
          default = lib.optionalString (config.services.ddclient.protocol == "nsupdate") "${pkgs.bind.dnsutils}/bin/nsupdate";
          defaultText = "";
          type = str;
          description = lib.mdDoc ''
            User name.
          '';
        };

        passwordFile = mkOption {
          default = null;
          type = nullOr str;
          description = lib.mdDoc ''
            A file containing the password or a TSIG key in named format when using the nsupdate protocol.
          '';
        };

        interval = mkOption {
          default = "10min";
          type = str;
          description = lib.mdDoc ''
            The interval at which to run the check and update.
            See {command}`man 7 systemd.time` for the format.
          '';
        };

        configFile = mkOption {
          default = null;
          type = nullOr path;
          description = lib.mdDoc ''
            Path to configuration file.
            When set this overrides the generated configuration from module options.
          '';
          example = "/root/nixos/secrets/ddclient.conf";
        };

        protocol = mkOption {
          default = "dyndns2";
          type = str;
          description = lib.mdDoc ''
            Protocol to use with dynamic DNS provider (see https://sourceforge.net/p/ddclient/wiki/protocols).
          '';
        };

        server = mkOption {
          default = "";
          type = str;
          description = lib.mdDoc ''
            Server address.
          '';
        };

        ssl = mkOption {
          default = true;
          type = bool;
          description = lib.mdDoc ''
            Whether to use SSL/TLS to connect to dynamic DNS provider.
          '';
        };

        quiet = mkOption {
          default = false;
          type = bool;
          description = lib.mdDoc ''
            Print no messages for unnecessary updates.
          '';
        };

        script = mkOption {
          default = "";
          type = str;
          description = lib.mdDoc ''
            script as required by some providers.
          '';
        };

        usev4 = mkOption {
          default = "webv4, webv4=checkip.dyndns.com/, webv4-skip='Current IP Address: '";
          type = str;
          description = lib.mdDoc ''
            Method to determine the IP address to send to the dynamic DNS provider.
          '';
        };

        usev6 = mkOption {
          default = "";
          type = str;
          description = lib.mdDoc ''
            Method to determine the IP address to send to the dynamic DNS provider.
          '';
        };

        verbose = mkOption {
          default = false;
          type = bool;
          description = lib.mdDoc ''
            Print verbose information.
          '';
        };

        zone = mkOption {
          default = "";
          type = str;
          description = lib.mdDoc ''
            zone as required by some providers.
          '';
        };

        extraConfig = mkOption {
          default = "";
          type = lines;
          description = lib.mdDoc ''
            Extra configuration. Contents will be added verbatim to the configuration file.

            ::: {.note}
            `daemon` should not be added here because it does not work great with the systemd-timer approach the service uses.
            :::
          '';
        };
      };
    };

    ###### implementation

    config = mkIf config.services.ddclient.enable {
      systemd.services.ddclient = {
        description = "Dynamic DNS Client";
        wantedBy = ["multi-user.target"];
        after = ["network.target"];
        restartTriggers = optional (cfg.configFile != null) cfg.configFile;

        serviceConfig = {
          DynamicUser = true;
          RuntimeDirectoryMode = "0700";
          inherit RuntimeDirectory;
          inherit StateDirectory;
          Type = "oneshot";
          ExecStartPre = "!${pkgs.writeShellScript "ddclient-prestart" preStart}";
          ExecStart = "${lib.getBin cfg.package}/bin/ddclient -file /run/${RuntimeDirectory}/ddclient.conf";
        };
      };

      systemd.timers.ddclient = {
        description = "Run ddclient";
        wantedBy = ["timers.target"];
        timerConfig = {
          OnBootSec = cfg.interval;
          OnUnitInactiveSec = cfg.interval;
        };
      };
    };
  }