Calendar: Update month view on first_day_of_week setting change

Now when the user changes their preferred first day of the week in the
Calendar Settings, the Calendar application and applet views are update
accordingly without needing to restart them.

Userland/Applications/Calendar/main.cpp

@@ -27,6 +27,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     auto app = TRY(GUI::Application::try_create(arguments));
 
     Config::pledge_domain("Calendar");
+    Config::monitor_domain("Calendar");
 
     TRY(Core::System::pledge("stdio recvfd sendfd rpath"));
     TRY(Core::System::unveil("/etc/timezone", "r"));

Userland/Libraries/LibGUI/Calendar.cpp

@@ -754,4 +754,13 @@ size_t Calendar::day_of_week_index(String const& day_name)
     auto const& day_names = AK::long_day_names;
     return AK::find_index(day_names.begin(), day_names.end(), day_name);
 }
+
+void Calendar::config_string_did_change(String const& domain, String const& group, String const& key, String const& value)
+{
+    VERIFY(domain == "Calendar");
+    if (group == "View" && key == "FirstDayOfWeek") {
+        m_first_day_of_week = static_cast<DayOfWeek>(day_of_week_index(value));
+        update_tiles(m_view_year, m_view_month);
+    }
+}
 }

Userland/Libraries/LibGUI/Calendar.h

@@ -8,13 +8,16 @@
 #pragma once
 
 #include <AK/String.h>
+#include <LibConfig/Listener.h>
 #include <LibCore/DateTime.h>
 #include <LibGUI/Frame.h>
 #include <LibGUI/Widget.h>
 
 namespace GUI {
 
-class Calendar final : public GUI::Frame {
+class Calendar final
+    : public GUI::Frame
+    , public Config::Listener {
     C_OBJECT(Calendar)
 
 public:
@@ -67,6 +70,8 @@ public:
         m_unadjusted_tile_size.set_height(height);
     }
 
+    virtual void config_string_did_change(String const&, String const&, String const&, String const&) override;
+
     Function<void()> on_tile_click;
     Function<void()> on_tile_doubleclick;
     Function<void()> on_month_click;

Userland/Services/Taskbar/main.cpp

@@ -50,6 +50,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     auto app = TRY(GUI::Application::try_create(arguments));
     Config::pledge_domains({ "Taskbar", "Calendar" });
     Config::monitor_domain("Taskbar");
+    Config::monitor_domain("Calendar");
     app->event_loop().register_signal(SIGCHLD, [](int) {
         // Wait all available children
         while (waitpid(-1, nullptr, WNOHANG) > 0)