nixos/factorio: add extraSettings and package options

Currently there is no way to set game settings, such as administrators.
extraSettings allows users to override default game settings without
adding many more settings.

The package option allows users to use the experimental version, or
override to a specific version with their own modified package.

nixos/modules/services/games/factorio.nix

@@ -4,14 +4,13 @@ with lib;
 
 let
   cfg = config.services.factorio;
-  factorio = pkgs.factorio-headless;
   name = "Factorio";
   stateDir = "/var/lib/${cfg.stateDirName}";
   mkSavePath = name: "${stateDir}/saves/${name}.zip";
   configFile = pkgs.writeText "factorio.conf" ''
     use-system-read-write-data-directories=true
     [path]
-    read-data=${factorio}/share/factorio/data
+    read-data=${cfg.package}/share/factorio/data
     write-data=${stateDir}
   '';
   serverSettings = {
@@ -37,7 +36,7 @@ let
     only_admins_can_pause_the_game = true;
     autosave_only_on_server = true;
     admins = [];
-  };
+  } // cfg.extraSettings;
   serverSettingsFile = pkgs.writeText "server-settings.json" (builtins.toJSON (filterAttrsRecursive (n: v: v != null) serverSettings));
   modDir = pkgs.factorio-utils.mkModDirDrv cfg.mods;
 in
@@ -115,6 +114,14 @@ in
           Description of the game that will appear in the listing.
         '';
       };
+      extraSettings = mkOption {
+        type = types.attrs;
+        default = {};
+        example = { admins = [ "username" ];};
+        description = ''
+          Extra game configuration that will go into server-settings.json
+        '';
+      };
       public = mkOption {
         type = types.bool;
         default = false;
@@ -136,6 +143,15 @@ in
           Your factorio.com login credentials. Required for games with visibility public.
         '';
       };
+      package = mkOption {
+        type = types.package;
+        default = pkgs.factorio-headless;
+        defaultText = "pkgs.factorio-headless";
+        example = "pkgs.factorio-headless-experimental";
+        description = ''
+          Factorio version to use. This defaults to the stable channel.
+        '';
+      };
       password = mkOption {
         type = types.nullOr types.str;
         default = null;
@@ -184,7 +200,7 @@ in
       preStart = toString [
         "test -e ${stateDir}/saves/${cfg.saveName}.zip"
         "||"
-        "${factorio}/bin/factorio"
+        "${cfg.package}/bin/factorio"
           "--config=${cfg.configFile}"
           "--create=${mkSavePath cfg.saveName}"
           (optionalString (cfg.mods != []) "--mod-directory=${modDir}")
@@ -197,7 +213,7 @@ in
         StateDirectory = cfg.stateDirName;
         UMask = "0007";
         ExecStart = toString [
-          "${factorio}/bin/factorio"
+          "${cfg.package}/bin/factorio"
           "--config=${cfg.configFile}"
           "--port=${toString cfg.port}"
           "--start-server=${mkSavePath cfg.saveName}"