views/month-view: Change visuals of out-of-month day cells

This still looks like garbage becase of the rudimentary way we
compute the current date, but it's a start.

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

@@ -721,3 +721,28 @@ gcal_month_view_row_remove_event (GcalMonthViewRow *self,
 
   GCAL_EXIT;
 }
+
+void
+gcal_month_view_row_update_style_for_date   (GcalMonthViewRow *self,
+                                             GDateTime        *date)
+{
+  g_autoptr (GDateTime) range_start = NULL;
+
+  g_assert (GCAL_IS_MONTH_VIEW_ROW (self));
+  g_assert (date != NULL);
+  g_assert (self->range != NULL);
+
+  range_start = gcal_range_get_start (self->range);
+
+  for (guint i = 0; i < 7; i++)
+    {
+      g_autoptr (GDateTime) cell_date = NULL;
+      gboolean different_month;
+
+      cell_date = g_date_time_add_days (range_start, i);
+      different_month = g_date_time_get_year (cell_date) != g_date_time_get_year (date) ||
+                        g_date_time_get_month (cell_date) != g_date_time_get_month (date);
+
+      gcal_month_cell_set_different_month (GCAL_MONTH_CELL (self->day_cells[i]), different_month);
+    }
+}

src/gui/views/gcal-month-view-row.h

@@ -50,4 +50,7 @@ void                 gcal_month_view_row_add_event               (GcalMonthViewR
 void                 gcal_month_view_row_remove_event            (GcalMonthViewRow   *self,
                                                                   GcalEvent          *event);
 
+void                 gcal_month_view_row_update_style_for_date   (GcalMonthViewRow   *self,
+                                                                  GDateTime          *date);
+
 G_END_DECLS

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

@@ -320,6 +320,12 @@ update_week_ranges (GcalMonthView *self,
         }
     }
 
+  for (gint i = 0; i < self->week_rows->len; i++)
+    {
+      GcalMonthViewRow *row = g_ptr_array_index (self->week_rows, i);
+      gcal_month_view_row_update_style_for_date (row, new_date);
+    }
+
   dump_row_ranges (self);
 }