{
  config,
  lib,
  pkgs,
  ...
}:
let
  cfg = config.services.finance-duck;
  address =
    if lib.hasInfix ":" cfg.listenAddress then "[${cfg.listenAddress}]" else cfg.listenAddress;
  validOrigin =
    builtins.match "https?://([A-Za-z0-9]([A-Za-z0-9.-]*[A-Za-z0-9])?|[[][0-9A-Fa-f:]+[]])(:[0-9]+)?" cfg.publicURL
    != null;
in
{
  options.services.finance-duck = {
    enable = lib.mkEnableOption "Finance Duck, a private financial dashboard without application authentication";
    package = lib.mkOption {
      type = lib.types.package;
      description = "Finance Duck package, including the embedded dashboard.";
    };
    publicURL = lib.mkOption {
      type = lib.types.str;
      description = "Exact HTTP(S) browser origin, including any non-default port, without a trailing slash or path.";
    };
    listenAddress = lib.mkOption {
      type = lib.types.str;
      default = "127.0.0.1";
      description = "HTTP listen address. Non-loopback listeners must be isolated by a firewall or VPN.";
    };
    port = lib.mkOption {
      type = lib.types.port;
      default = 8080;
      description = "HTTP listen port; the native module does not open the firewall.";
    };
    environmentFile = lib.mkOption {
      type = lib.types.nullOr lib.types.str;
      default = null;
      description = ''
        Absolute runtime environment-file path, never a Nix store path.
        Optional startup fallbacks; both providers can be configured in Settings.
        When configured, the file must exist. For banking, set ENABLEBANKING_APP_ID,
        ENABLEBANKING_KEY_FILE and ENABLEBANKING_REDIRECT_URL together.
        OPENROUTER_API_KEY is the optional AI fallback. For each provider,
        saved UI configuration or explicit removal overrides its environment.
        The environment file may be root:root 0600; the referenced private key must
        be readable by finance-duck (for example root:finance-duck 0640).
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    assertions = [
      {
        assertion = validOrigin;
        message = "services.finance-duck.publicURL must be an exact HTTP(S) origin, without userinfo, path, query or fragment.";
      }
      {
        assertion = cfg.listenAddress != "" && builtins.match "[A-Za-z0-9.:_-]+" cfg.listenAddress != null;
        message = "services.finance-duck.listenAddress must be a nonempty address without brackets or a port.";
      }
      {
        assertion =
          cfg.environmentFile == null
          || (
            lib.hasPrefix "/" cfg.environmentFile
            && !lib.hasPrefix "/nix/store/" cfg.environmentFile
            && builtins.match "/[A-Za-z0-9_./-]+" cfg.environmentFile != null
            && !(lib.elem ".." (lib.splitString "/" cfg.environmentFile))
          );
        message = "services.finance-duck.environmentFile must be an absolute runtime path outside /nix/store, with no parent-directory traversal.";
      }
    ];

    users.groups.finance-duck = { };
    users.users.finance-duck = {
      isSystemUser = true;
      group = "finance-duck";
      home = "/var/lib/finance-duck";
    };

    systemd.services.finance-duck = {
      description = "Finance Duck private financial dashboard";
      wantedBy = [ "multi-user.target" ];
      wants = [ "network-online.target" ];
      after = [ "network-online.target" ];
      environment.HOME = "/var/lib/finance-duck";
      serviceConfig = {
        ExecStart = lib.escapeShellArgs [
          "${cfg.package}/bin/finance-duck"
          "-data"
          "/var/lib/finance-duck"
          "-listen"
          "${address}:${toString cfg.port}"
          "-public-url"
          cfg.publicURL
        ];
        User = "finance-duck";
        Group = "finance-duck";
        StateDirectory = "finance-duck";
        StateDirectoryMode = "0700";
        WorkingDirectory = "/var/lib/finance-duck";
        UMask = "0077";
        Restart = "on-failure";
        RestartSec = "5s";
        TimeoutStopSec = "30s";
        NoNewPrivileges = true;
        ProtectSystem = "strict";
        ProtectHome = true;
        PrivateTmp = true;
        PrivateDevices = true;
        CapabilityBoundingSet = "";
      }
      // lib.optionalAttrs (cfg.environmentFile != null) {
        EnvironmentFile = cfg.environmentFile;
      };
    };
  };
}