nixos/neard: expose settings option

nixos/modules/services/desktops/neard.nix

@@ -1,16 +1,69 @@
-# neard service.
-{ config, lib, pkgs, ... }:
 {
-  ###### interface
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+let
+  inherit (lib)
+    mkEnableOption
+    mkIf
+    mkOption
+    types
+  ;
+  cfg = config.services.neard;
+  format = pkgs.formats.ini { };
+  configFile = format.generate "neard.conf" cfg.settings;
+in
+{
+  options.services.neard = {
+    enable = mkEnableOption "neard, an NFC daemon";
+
+    settings = mkOption {
+      type = types.submodule {
+        freeformType = format.type;
         options = {
-    services.neard = {
+          General = {
-      enable = lib.mkEnableOption "neard, an NFC daemon";
+            ConstantPoll = mkOption {
+              type = types.bool;
+              default = false;
+              description = ''
+                Enable constant polling. Constant polling will automatically trigger a new
+                polling loop whenever a tag or a device is no longer in the RF field.
+              '';
+            };
+
+            DefaultPowered = mkOption {
+              type = types.bool;
+              default = true;
+              description = ''
+                Automatically turn an adapter on when being discovered.
+              '';
+            };
+
+            ResetOnError = mkOption {
+              type = types.bool;
+              default = true;
+              description = ''
+                Power cycle the adapter when getting a driver error from the kernel.
+              '';
+            };
+          };
+        };
+      };
+      default = {};
+      description = ''
+        Neard INI-style configuration file as a Nix attribute set.
+
+        See the upstream [configuration file](https://github.com/linux-nfc/neard/blob/master/src/main.conf).
+      '';
     };
   };
 
+  config = mkIf cfg.enable {
+    environment.etc."neard/main.conf".source = configFile;
 
-  ###### implementation
-  config = lib.mkIf config.services.neard.enable {
     environment.systemPackages = [ pkgs.neard ];
 
     services.dbus.packages = [ pkgs.neard ];