[gnome-calendar/wip/mcatanzaro/timezone: 1/5] edit-dialog: Fix timezone for events created in month view

[Michael Catanzaro <mcatanzaro src gnome org>]

commit ce8e8c217eaa299c13365728a25fe5466969a871
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.

 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 31cd0a0..01a34f0 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);