[gnome-calendar/cherry-pick-ce8e8c21] edit-dialog: Fix timezone for events created in month view

[Michael Catanzaro <mcatanzaro src gnome org>]

commit d04a603472a2467e5cb75b03114e51f91e12d3f6
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Tue Dec 5 16:28:18 2017 -0600

    edit-dialog: Fix timezone for events created in month view
    
    In month view, when clicking on a day of the month, every event is
    initially an All Day event until the user opens the Edit Details dialog
    and unchecks the checkbox. This means that the event is originally
    created in UTC time, and needs to be explicitly switched to local time.
    
    
    (cherry picked from commit ce8e8c217eaa299c13365728a25fe5466969a871)

 src/gcal-edit-dialog.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)
---
diff --git a/src/gcal-edit-dialog.c b/src/gcal-edit-dialog.c
index 359b94a0..fbba3a1c 100644
--- a/src/gcal-edit-dialog.c
+++ b/src/gcal-edit-dialog.c
@@ -452,6 +452,7 @@ action_button_clicked (GtkWidget *widget,
       GcalRecurrenceFrequency freq;
       GcalRecurrence *old_recur;
       GDateTime *start_date, *end_date;
+      gboolean was_all_day;
       gboolean all_day;
       gchar *note_text;
 
@@ -468,6 +469,7 @@ action_button_clicked (GtkWidget *widget,
 
       /* Update all day */
       all_day = gtk_toggle_button_get_active (GTK_TOGGLE_BUTTON (dialog->all_day_check));
+      was_all_day = gcal_event_get_all_day (dialog->event);
 
       gcal_event_set_all_day (dialog->event, all_day);
 
@@ -483,7 +485,7 @@ action_button_clicked (GtkWidget *widget,
 
       /*
        * Update start & end dates. The dates are already translated to the current
-       * timezone.
+       * timezone (unless the event used to be all day, but no longer is).
        */
       start_date = gcal_edit_dialog_get_date_start (dialog);
       end_date = gcal_edit_dialog_get_date_end (dialog);
@@ -500,6 +502,23 @@ action_button_clicked (GtkWidget *widget,
           g_clear_pointer (&end_date, g_date_time_unref);
           end_date = fake_end_date;
         }
+      else if (!all_day && was_all_day)
+        {
+          /* When an all day event is changed to be not an all day event, we
+           * need to correct for the fact that the event's timezone was until
+           * now set to UTC. That means we need to change the timezone to
+           * localtime now, or else it will be saved incorrectly.
+           */
+          GDateTime *localtime_date;
+
+          localtime_date = g_date_time_to_local (start_date);
+          g_clear_pointer (&start_date, g_date_time_unref);
+          start_date = localtime_date;
+
+          localtime_date = g_date_time_to_local (end_date);
+          g_clear_pointer (&end_date, g_date_time_unref);
+          end_date = localtime_date;
+        }
 
       gcal_event_set_date_start (dialog->event, start_date);
       gcal_event_set_date_end (dialog->event, end_date);