gui: Use the new GcalContext API to get week start day once

This gets the globally set start-of-week setting on application startup.
Making the views redraw themselves on setting change while running will
be a later step.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/822>

src/gui/common/gcal-date-chooser.c

@@ -1083,7 +1083,7 @@ gcal_date_chooser_init (GcalDateChooser *self)
   self->date = g_date_time_new_now_local ();
   g_date_time_get_ymd (self->date, &self->this_year, NULL, NULL);
 
-  self->week_start = gcal_util_get_first_weekday_iso ();
+  self->week_start = gcal_context_get_week_start_day (context);
 
   gtk_widget_init_template (GTK_WIDGET (self));
 

src/gui/views/gcal-month-view.c

@@ -19,9 +19,10 @@
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
+#include "config.h"
+
 #define G_LOG_DOMAIN "GcalMonthView"
 
-#include "config.h"
 #include "gcal-debug.h"
 #include "gcal-event-widget-pool.h"
 #include "gcal-gui-utils.h"
@@ -194,7 +195,9 @@ allocate_overflow_popover (GcalMonthView *self,
 static inline void
 update_weekday_labels (GcalMonthView *self)
 {
-  const gint first_weekday = gcal_util_get_first_weekday_iso ();
+  GcalContext *context = gcal_application_get_context (GCAL_DEFAULT_APPLICATION);
+
+  const gint first_weekday = gcal_context_get_week_start_day (context);
 
   for (gint i = 0; i < GCAL_N_WEEKDAYS; i++)
     {

src/utils/gcal-date-time-utils.c

@@ -19,6 +19,8 @@
  */
 
 #include "gcal-date-time-utils.h"
+#include "gcal-application.h"
+#include "gcal-context.h"
 #include "gcal-utils.h"
 
 /**
@@ -76,6 +78,9 @@ gcal_date_time_get_days_in_month (GDateTime *date)
 GDateTime*
 gcal_date_time_get_start_of_week (GDateTime *date)
 {
+  GcalContext *context = gcal_application_get_context (GCAL_DEFAULT_APPLICATION);
+  g_assert (GCAL_IS_CONTEXT (context));
+
   g_autoptr (GDateTime) start_of_week = NULL;
   gint n_days_after_week_start;
   gint first_weekday;
@@ -83,7 +88,7 @@ gcal_date_time_get_start_of_week (GDateTime *date)
 
   g_assert (date != NULL);
 
-  first_weekday = gcal_util_get_first_weekday_iso ();
+  first_weekday = gcal_context_get_week_start_day (context);
   weekday = g_date_time_get_day_of_week (date) % GCAL_N_WEEKDAYS;
   n_days_after_week_start = (GCAL_N_WEEKDAYS + weekday - first_weekday) % GCAL_N_WEEKDAYS;