Make machine ID a option

nixosModules/clanCore/machine-id/default.nix

@@ -0,0 +1,53 @@
+{
+  lib,
+  config,
+  pkgs,
+  ...
+}:
+let
+  var = config.clan.core.vars.generators.machine-id.files.machineId or { };
+in
+{
+
+  options.clan.core.settings.machine-id = {
+    enable = lib.mkEnableOption ''
+      machine ID generation. Sets the /etc/machine-id and exposes it as a nix
+      option. This unique ID that is not dependent on ephemeral or
+      variable data, such as hostnames, MAC addresses or IP addresses.
+
+      See https://www.freedesktop.org/software/systemd/man/latest/machine-id.html for details.
+    '';
+  };
+
+  config = lib.mkIf (config.clan.core.settings.machine-id.enable) {
+
+    assertions = [
+      {
+        assertion = lib.stringLength var.value == 32;
+        message = "machine ID must be exactly 32 characters long.";
+      }
+    ];
+
+    boot.kernelParams = [
+      ''systemd.machine_id=${var.value}''
+    ];
+
+    environment.etc."machine-id".text = var.value;
+
+    clan.core.vars.generators.machine-id = {
+      files.machineId.secret = false;
+      runtimeInputs = [
+        pkgs.coreutils
+        pkgs.bash
+      ];
+      script = ''
+        uuid=$(bash ${./uuid4.sh})
+
+        # Remove the hyphens from the UUID
+        uuid_no_hyphens=$(echo -n "$uuid" | tr -d '-')
+
+        echo -n "$uuid_no_hyphens" > "$out/machineId"
+      '';
+    };
+  };
+}