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

with lib;

let

  nssModulesPath = config.system.nssModules.path;
  cfg = config.services.nscd;

in

{

  ###### interface

  options = {

    services.nscd = {

      enable = mkOption {
        type = types.bool;
        default = true;
        description = ''
          Whether to enable the Name Service Cache Daemon.
          Disabling this is strongly discouraged, as this effectively disables NSS Lookups
          from all non-glibc NSS modules, including the ones provided by systemd.
        '';
      };

      config = mkOption {
        type = types.lines;
        default = builtins.readFile ./nscd.conf;
        description = "Configuration to use for Name Service Cache Daemon.";
      };

      package = mkOption {
        type = types.package;
        default = if pkgs.stdenv.hostPlatform.libc == "glibc"
          then pkgs.stdenv.cc.libc.bin
          else pkgs.glibc.bin;
        defaultText = lib.literalExpression ''
          if pkgs.stdenv.hostPlatform.libc == "glibc"
            then pkgs.stdenv.cc.libc.bin
            else pkgs.glibc.bin;
        '';
        description = "package containing the nscd binary to be used by the service";
      };

    };

  };


  ###### implementation

  config = mkIf cfg.enable {
    environment.etc."nscd.conf".text = cfg.config;

    systemd.services.nscd =
      { description = "Name Service Cache Daemon";

        before = [ "nss-lookup.target" "nss-user-lookup.target" ];
        wants = [ "nss-lookup.target" "nss-user-lookup.target" ];
        wantedBy = [ "multi-user.target" ];

        environment = { LD_LIBRARY_PATH = nssModulesPath; };

        restartTriggers = [
          config.environment.etc.hosts.source
          config.environment.etc."nsswitch.conf".source
          config.environment.etc."nscd.conf".source
        ];

        # We use DynamicUser because in default configurations nscd doesn't
        # create any files that need to survive restarts. However, in some
        # configurations, nscd needs to be started as root; it will drop
        # privileges after all the NSS modules have read their configuration
        # files. So prefix the ExecStart command with "!" to prevent systemd
        # from dropping privileges early. See ExecStart in systemd.service(5).
        serviceConfig =
          { ExecStart = "!@${cfg.package}/bin/nscd nscd";
            Type = "forking";
            DynamicUser = true;
            RuntimeDirectory = "nscd";
            PIDFile = "/run/nscd/nscd.pid";
            Restart = "always";
            ExecReload =
              [ "${cfg.package}/bin/nscd --invalidate passwd"
                "${cfg.package}/bin/nscd --invalidate group"
                "${cfg.package}/bin/nscd --invalidate hosts"
              ];
          };
      };

  };
}