[gnome-calendar] year-view: Fix for 01-01-2017 date

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 9646d4f543a42ae7a57e9ad5426904ecf571defc
Author: Isaque Galdino <igaldino gmail com>
Date:   Fri Jan 29 23:31:23 2016 -0200

    year-view: Fix for 01-01-2017 date
    
    Previous fix was considering Jan 1st and Dec 31st to find the week
    number, using ISO 8601 standard, and that was causing an issue with some
    dates like Jan 1st, 2017 which was displaying week# 52 instead of
    week #1.
    
    The issue happened because ISO 8601 always consider Monday as the first
    weekday, so as Jan 1st, 2017 is a Sunday, it' still considered week# 52
    and not week# 1.
    
    After checking GtkCalendar code I noticed it uses the same ISO 8601
    standard but instead of using Jan 1st or Dec 31st, it always get the
    week number based on the last day of that week, taking account if the
    week starts on Sunday or Monday, depending on the locale. In our
    example, using a calendar based on Sunday, Jan 1st, 2017 is the first
    day of the week and Jan 7th, 2017 is the last one. Therefore I changed
    week number code to always use the last day of the week.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=757622

 src/gcal-year-view.c |   32 +++++++++++++++++++++++++-------
 1 files changed, 25 insertions(+), 7 deletions(-)
---
diff --git a/src/gcal-year-view.c b/src/gcal-year-view.c
index 503a21f..abd0ea8 100644
--- a/src/gcal-year-view.c
+++ b/src/gcal-year-view.c
@@ -119,6 +119,26 @@ G_DEFINE_TYPE_WITH_CODE (GcalYearView, gcal_year_view, GTK_TYPE_BOX,
                          G_IMPLEMENT_INTERFACE (E_TYPE_CAL_DATA_MODEL_SUBSCRIBER,
                                                 gcal_data_model_subscriber_interface_init));
 
+static guint
+get_last_week_of_year_dmy (gint       first_weekday,
+                           GDateDay   day,
+                           GDateMonth month,
+                           GDateYear  year)
+{
+  GDate day_of_year;
+  gint day_of_week;
+
+  g_date_set_dmy (&day_of_year, day, month, year);
+  day_of_week = g_date_get_weekday (&day_of_year) % 7;
+
+  if (day_of_week >= first_weekday)
+    g_date_add_days (&day_of_year, (6 - day_of_week) + first_weekday);
+  else
+    g_date_add_days (&day_of_year, first_weekday - day_of_week - 1);
+
+  return g_date_get_iso8601_week_of_year (&day_of_year);
+}
+
 static void
 update_date (GcalYearView *year_view,
              icaltimetype *new_date)
@@ -128,6 +148,11 @@ update_date (GcalYearView *year_view,
 
   g_clear_pointer (&year_view->date, g_free);
   year_view->date = new_date;
+
+  year_view->first_week_of_year = get_last_week_of_year_dmy (year_view->first_weekday,
+                                                             1, G_DATE_JANUARY,  year_view->date->year);;
+  year_view->last_week_of_year = get_last_week_of_year_dmy (year_view->first_weekday,
+                                                            31, G_DATE_DECEMBER, year_view->date->year);
 }
 
 static void
@@ -793,7 +818,6 @@ draw_navigator (GcalYearView *year_view,
   gint header_padding_left, header_padding_top, header_height, layout_width, layout_height;
   gint real_padding_left, real_padding_top, i, sw, weeks_counter;
   gdouble width, height, box_side;
-  GDate day_of_year;
 
   gchar *header_str;
 
@@ -844,12 +868,6 @@ draw_navigator (GcalYearView *year_view,
   real_padding_top = (height - (7 * 3 * box_side)) / 4.0;
 
   year_view->navigator_grid->box_side = box_side;
-
-  /* get first and last weeks of the year */
-  g_date_set_dmy (&day_of_year, 1, G_DATE_JANUARY, year_view->date->year);
-  year_view->first_week_of_year = g_date_get_iso8601_week_of_year (&day_of_year);
-  g_date_set_dmy (&day_of_year, 31, G_DATE_DECEMBER, year_view->date->year);
-  year_view->last_week_of_year = g_date_get_iso8601_week_of_year (&day_of_year);
   weeks_counter = year_view->first_week_of_year;
   for (i = 0; i < 12; i++)
     {