refactor(waybar): register custom modules

configs/nixos/modules/network/vpn-client.nix

@@ -1,10 +1,30 @@
 {
   config,
   lib,
+  pkgs,
   ...
 }:
 let
   cfg = config.modules.network.vpn-client; # NOLINT(let_order)
+
+  vpnIcon = builtins.fromJSON ''"\udb83\udc9d"'';
+
+  vpnStatus = pkgs.writeShellScript "waybar-vpn-status" ''
+    interface=${lib.escapeShellArg cfg.interface}
+
+    if ! ${lib.getExe' pkgs.iproute2 "ip"} link show dev "$interface" >/dev/null 2>&1; then
+      printf '{"text":"","class":"idle"}\n'
+      exit 0
+    fi
+
+    ipaddr=$(${lib.getExe' pkgs.iproute2 "ip"} -4 -o addr show dev "$interface" | ${lib.getExe' pkgs.gawk "awk"} '{ print $4; exit }')
+
+    ${lib.getExe pkgs.jq} -cn \
+      --arg text "${vpnIcon}" \
+      --arg tooltip "VPN $interface: ''${ipaddr:-no IPv4}" \
+      --arg class "active" \
+      '{ text: $text, tooltip: $tooltip, class: $class }'
+  '';
 in
 {
   options.modules.network.vpn-client = {
@@ -57,6 +77,15 @@ in
       vpn-off = "sudo systemctl stop 'wireguard-${cfg.interface}*.service' wireguard-${cfg.interface}.target";
     };
 
+    registry.waybar-module.${config.networking.hostName}."custom/vpn" = {
+      order = 50;
+      settings = {
+        return-type = "json";
+        exec = "${vpnStatus}";
+        interval = 5;
+      };
+    };
+
     systemd.targets."wireguard-${cfg.interface}".wantedBy = lib.mkForce [ ];
 
     networking.wireguard.interfaces.${cfg.interface} = {