Add NixOS module

module.nix

@@ -0,0 +1,56 @@
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.services.bang-evaluator;
+in
+{
+  options.services.bang-evaluator = {
+    enable = lib.mkEnableOption "bang-evaluator";
+    package = lib.mkOption {
+      type = lib.types.package;
+      default = import ./default.nix { inherit pkgs; };
+      example = "pkgs.bang-exporter-fork";
+      description = "The package to use for bang-exporter";
+    };
+    listenAddress = lib.mkOption {
+      type = lib.types.str;
+      default = ":8081";
+      example = "localhost:8081";
+      description = "The address bang-evaluator should listen on.";
+    };
+  };
+
+  config = {
+    systemd.services.bang-evaluator = lib.mkIf cfg.enable {
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+      environment = {
+        BANG_EVALUATOR_LISTEN_ADDRESS = cfg.listenAddress;
+      };
+      serviceConfig = {
+        ExecStart = "${cfg.package}/bin/evaluator";
+        Restart = "always";
+
+        # taken from systemd-analyze --no-pager security bang-evaluator.service
+        # probably overkill
+        CapabilityBoundingSet = null;
+        DynamicUser = true;
+        LockPersonality = true;
+        MemoryDenyWriteExecute = true;
+        PrivateDevices = true;
+        PrivateUsers = true;
+        ProtectClock = true;
+        ProtectControlGroups = true;
+        ProtectHome = true;
+        ProtectHostname = true;
+        ProtectKernelLogs = true;
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        RestrictAddressFamilies = [ "AF_INET" "AF_INET6" ];
+        RestrictNamespaces = true;
+        RestrictRealtime = true;
+        SystemCallArchitectures = "native";
+        SystemCallFilter = "@system-service";
+      };
+    };
+  };
+}