refactor: make the whole thing more generic

modules/nixos/services/airprint.nix

@@ -0,0 +1,23 @@
+{ pkgs, lib, config, ... }:
+with lib;
+
+let cfg = config.services.airprint;
+
+in {
+  options.services.airprint = {
+    enable = mkEnableOption "Enable printing over the air using sane and avahi";
+  };
+
+  config = mkIf cfg.enable {
+    hardware.sane = {
+      enable = true;
+      extraBackends = [ pkgs.sane-airscan ];
+    };
+    services.printing.enable = true;
+    services.avahi = {
+      enable = true;
+      nssmdns4 = true;
+      openFirewall = true;
+    };
+  };
+}