@@ -123,6 +123,34 @@ cfg = config.services.mycal;
             settingsFormat = pkgs.formats.toml { };
 
             inherit (lib) mkEnableOption mkOption mkIf types;
+
+            calendarOptionType = types.submodule {
+              options = {
+                file = mkOption {
+                  type = with types; nullOr str;
+                  default = "";
+                  example = "/path/to/calendar/file";
+                  description = ''
+                    Path to the calendar file. Preferred over URL.
+                  '';
+                };
+                url = mkOption {
+                  type = with types; nullOr str;
+                  default = "";
+                  example = "https://example.com/calendar.ics";
+                  description = ''
+                    URL to the calendar file.
+                  '';
+                };
+                all_tentative = mkOption {
+                  type = types.bool;
+                  default = false;
+                  description = ''
+                    Whether all events from this calendar should be marked as tentative.
+                  '';
+                };
+              };
+            };
           in
           {
             options.services.mycal = {
@@ -179,28 +207,31 @@
                     calendar = mkOption {
                       default = { };
                       description = ''
-                        Configuration for the calendar. Either a file or a URL must be provided.
+                        Configuration for a single calendar. Either a file or a URL must be provided.
+                        This option is kept for backward compatibility. Using the calendars option
+                        is recommended for new configurations.
+
+                        Note: This option is deprecated and will be removed in a future release.
                       '';
-                      type = types.submodule {
-                        options = {
-                          file = mkOption {
-                            type = types.str;
-                            default = "";
-                            example = "/path/to/calendar/file";
-                            description = ''
-                              Path to the calendar file. Preferred over URL.
-                            '';
-                          };
-                          url = mkOption {
-                            type = types.str;
-                            default = "";
-                            example = "https://example.com/calendar.ics";
-                            description = ''
-                              URL to the calendar file.
-                            '';
-                          };
-                        };
-                      };
+                      type = calendarOptionType;
+                    };
+
+                    calendars = mkOption {
+                      default = [ ];
+                      description = ''
+                        Configuration for multiple calendars. This option will be appended to the
+                        singular calendar option if both are specified.
+                      '';
+                      type = types.listOf calendarOptionType;
+                    };
+
+                    email = mkOption {
+                      type = types.str;
+                      default = "";
+                      example = "john.doe@example.com";
+                      description = ''
+                        Email address of the user.
+                      '';
                     };
                   };
                 };
@@ -208,6 +239,21 @@ };
             };
 
             config = mkIf cfg.enable {
+              # Validate configuration
+              assertions = [
+                {
+                  assertion = with cfg.settings;
+                    (calendars != [ ] && builtins.any (cal: cal.file != "" || cal.url != "") calendars) ||
+                      (calendar.file != "" || calendar.url != "");
+                  message = "At least one calendar must be configured with either a file or URL in either settings.calendar or settings.calendars";
+                }
+              ];
+
+              # Issue deprecation warning if the calendar option is used
+              warnings = lib.optional
+                (cfg.settings.calendar.file != "" || cfg.settings.calendar.url != "")
+                "The settings.calendar option is deprecated and will be removed in a future release. Please use the settings.calendars option instead.";
+
               systemd.services.mycal = {
                 description = "Mycal Calendar Service";