feat: Implemented madd client module

flake.nix

@@ -40,7 +40,7 @@
       overlays.madd = final: prev: mkPackages final;
       overlays.default = overlays.madd;
 
-      nixosModules.madd = import ./nixos.nix;
+      nixosModules.madd = import ./nixos.nix { overlay = overlays.madd; };
       nixosModules.default = nixosModules.madd;
     };
 }

nixos.nix

@@ -1,12 +1,78 @@
-{ lib, config, ... }:
+{ overlay }:
+
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}:
 
 with lib;
 {
-  option.madd-client = {
+  options.services.madd-client = {
     enable = mkEnableOption "MADD client";
+    endpoint = mkOption {
+      type = types.str;
+      description = "Endpoint for MADD client to connect to.";
+    };
+    interface = mkOption {
+      type = types.str;
+      default = "eth0";
+      description = "Network interface to use for MADD client.";
+    };
+    priv-key-file = mkOption {
+      type = types.str;
+      default = "/etc/ssh/ssh_host_ed25519_key";
+      description = "Path to the private SSH key file identifying this machine.";
+    };
+    pub-key-file = mkOption {
+      type = types.str;
+      default = "${config.services.madd-client.priv_key_file}.pub";
+      description = "Path to the public SSH key file identifying this machine.";
+    };
+    hostname = mkOption {
+      type = types.str;
+      default = config.networking.hostName;
+      description = "Hostname to use for MADD client.";
+    };
   };
 
-  options.madd-server = {
+  options.services.madd-server = {
     enable = mkEnableOption "MADD server";
   };
+
+  config = {
+    nixpkgs.overlays = [ overlay ];
+  }
+  // (
+    let
+      cfg = config.services.madd-client;
+    in
+    optionalAttrs config.madd-client.enable {
+      systemd.services.madd-client = {
+        description = "MADD Client Service";
+        wantedBy = [ "multi-user.target" ];
+        before = [ "network-pre.target" ];
+        requires = [ "network-pre.target" ];
+        script = ''
+          ${pkgs.iproute2}/bin/ip -4 monitor address label dev "${cfg.interface}" | while read -r event; do
+            if [[ $event == \[ADDR\]* ]]; then
+              ipv4=$(${pkgs.iproute2}/bin/ip -4 addr show dev "${cfg.interface}" | grep -Po 'inet \K[\d.]+')
+              if [ -n "$ipv4" ]; then
+
+                export MADD_ENDPOINT="${cfg.endpoint}"
+                export MADD_PRIV_KEY="${cfg.priv-key-file}"
+                export MADD_PUB_KEY="${cfg.pub-key-file}"
+                export MADD_HOSTNAME="${cfg.hostname}"
+                export MADD_IP="$ipv4"
+
+                ${pkgs.madd-client}/bin/madd-client
+              fi
+          done
+        '';
+      };
+    }
+  )
+  // (optionalAttrs config.madd-server.enable {
+  });
 }