add unused calendar application placeholder

modules/nixos/applications/calendar.nix

@@ -0,0 +1,37 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+{
+
+  options = {
+    calendar = {
+      enable = lib.mkEnableOption {
+        description = "Enable calendar.";
+        default = false;
+      };
+    };
+  };
+
+  config = lib.mkIf (config.gui.enable && config.calendar.enable) {
+    home-manager.users.${config.user} = {
+
+      accounts.calendar.accounts.default = {
+        basePath = "other/calendars"; # Where to save calendars in ~ directory
+        name = "personal";
+        local.type = "filesystem";
+        primary = true;
+        remote = {
+          passwordCommand = [ "" ];
+          type = "caldav";
+          url = "https://${config.hostnames.content}/remote.php/dav/principals/users/${config.user}";
+          userName = config.user;
+        };
+      };
+
+      home.packages = with pkgs; [ gnome-calendar ];
+    };
+  };
+}

modules/nixos/applications/default.nix

@@ -2,6 +2,7 @@
 {
 
   imports = [
+    ./calendar.nix
     ./calibre.nix
     ./nautilus.nix
   ];