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

with lib;

let

  cfg = config.services.xinetd;

  configFile = pkgs.writeText "xinetd.conf"
    ''
      defaults
      {
        log_type       = SYSLOG daemon info
        log_on_failure = HOST
        log_on_success = PID HOST DURATION EXIT
        ${cfg.extraDefaults}
      }

      ${concatMapStrings makeService cfg.services}
    '';

  makeService = srv:
    ''
      service ${srv.name}
      {
        protocol    = ${srv.protocol}
        ${optionalString srv.unlisted "type        = UNLISTED"}
        ${optionalString (srv.flags != "") "flags = ${srv.flags}"}
        socket_type = ${if srv.protocol == "udp" then "dgram" else "stream"}
        ${if srv.port != 0 then "port        = ${toString srv.port}" else ""}
        wait        = ${if srv.protocol == "udp" then "yes" else "no"}
        user        = ${srv.user}
        server      = ${srv.server}
        ${optionalString (srv.serverArgs != "") "server_args = ${srv.serverArgs}"}
        ${srv.extraConfig}
      }
    '';

in

{

  ###### interface

  options = {

    services.xinetd.enable = mkEnableOption "the xinetd super-server daemon";

    services.xinetd.extraDefaults = mkOption {
      default = "";
      type = types.lines;
      description = lib.mdDoc ''
        Additional configuration lines added to the default section of xinetd's configuration.
      '';
    };

    services.xinetd.services = mkOption {
      default = [];
      description = lib.mdDoc ''
        A list of services provided by xinetd.
      '';

      type = with types; listOf (submodule ({

        options = {

          name = mkOption {
            type = types.str;
            example = "login";
            description = lib.mdDoc "Name of the service.";
          };

          protocol = mkOption {
            type = types.str;
            default = "tcp";
            description =
              lib.mdDoc "Protocol of the service.  Usually `tcp` or `udp`.";
          };

          port = mkOption {
            type = types.int;
            default = 0;
            example = 123;
            description = lib.mdDoc "Port number of the service.";
          };

          user = mkOption {
            type = types.str;
            default = "nobody";
            description = lib.mdDoc "User account for the service";
          };

          server = mkOption {
            type = types.str;
            example = "/foo/bin/ftpd";
            description = lib.mdDoc "Path of the program that implements the service.";
          };

          serverArgs = mkOption {
            type = types.separatedString " ";
            default = "";
            description = lib.mdDoc "Command-line arguments for the server program.";
          };

          flags = mkOption {
            type = types.str;
            default = "";
            description = "";
          };

          unlisted = mkOption {
            type = types.bool;
            default = false;
            description = lib.mdDoc ''
              Whether this server is listed in
              {file}`/etc/services`.  If so, the port
              number can be omitted.
            '';
          };

          extraConfig = mkOption {
            type = types.lines;
            default = "";
            description = lib.mdDoc "Extra configuration-lines added to the section of the service.";
          };

        };

      }));

    };

  };


  ###### implementation

  config = mkIf cfg.enable {
    systemd.services.xinetd = {
      description = "xinetd server";
      after = [ "network.target" ];
      wantedBy = [ "multi-user.target" ];
      path = [ pkgs.xinetd ];
      script = "exec xinetd -syslog daemon -dontfork -stayalive -f ${configFile}";
    };
  };
}