[gnome-calendar] week-header: improve drag and drop

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

commit 0dcf86b7c2c424766f3601517bf155a283890983
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Tue Mar 14 20:19:28 2017 -0300

    week-header: improve drag and drop
    
    The rudimentary drag n' drop support should also deal
    with the following corner cases:
    
               All Day
    Multiday |   TRUE   |   FALSE    |
             |----------|------------|
        TRUE |   utc    | no changes |
       FALSE |   utc    |    utc     |
    
    https://bugzilla.gnome.org/show_bug.cgi?id=777424

 src/views/gcal-week-header.c |   52 ++++++++++++++++++++++++++++++++---------
 1 files changed, 40 insertions(+), 12 deletions(-)
---
diff --git a/src/views/gcal-week-header.c b/src/views/gcal-week-header.c
index bfa3ccf..b6fc1dc 100644
--- a/src/views/gcal-week-header.c
+++ b/src/views/gcal-week-header.c
@@ -1405,6 +1405,8 @@ gcal_week_header_drag_drop (GtkWidget      *widget,
   GcalWeekHeader *self;
   g_autoptr (GDateTime) week_start;
   g_autoptr (GDateTime) dnd_date;
+  GDateTime *start_date;
+  GDateTime *end_date;
   GtkWidget *event_widget;
   GcalEvent *event;
   gboolean ltr;
@@ -1422,30 +1424,56 @@ gcal_week_header_drag_drop (GtkWidget      *widget,
 
   /* RTL languages swap the drop cell column */
   if (!ltr)
-    {
-      drop_cell = 6 - drop_cell;
-    }
+    drop_cell = 6 - drop_cell;
 
   event = gcal_event_widget_get_event (GCAL_EVENT_WIDGET (event_widget));
+  start_date = gcal_event_get_date_start (event);
+  end_date = gcal_event_get_date_end (event);
   week_start = get_start_of_week (self->active_date);
-  dnd_date = g_date_time_add_days (week_start, drop_cell);
 
-  /*
-   * Set the event's start and end dates. Since the event may have a
-   * NULL end date, so we have to check it here
-   */
-  gcal_event_set_all_day (event, TRUE);
-  gcal_event_set_date_start (event, dnd_date);
+  if (gcal_event_is_multiday (event) && !gcal_event_get_all_day (event))
+    {
+      /*
+       * The only case where we don't touch the timezone is for
+       * timed, multiday events.
+       */
+      dnd_date = g_date_time_new (gcal_event_get_timezone (event),
+                                  g_date_time_get_year (week_start),
+                                  g_date_time_get_month (week_start),
+                                  g_date_time_get_day_of_month (week_start) + drop_cell,
+                                  g_date_time_get_hour (start_date),
+                                  g_date_time_get_minute (start_date),
+                                  0);
+    }
+  else
+    {
+      dnd_date = g_date_time_new_utc (g_date_time_get_year (week_start),
+                                      g_date_time_get_month (week_start),
+                                      g_date_time_get_day_of_month (week_start) + drop_cell,
+                                      0, 0, 0);
+
+      gcal_event_set_all_day (event, TRUE);
+    }
 
-  if (gcal_event_get_date_end (event))
+  /* Since the event may have a NULL end date, so we have to check it here */
+  if (end_date)
     {
       g_autoptr (GDateTime) new_end;
+      GTimeSpan difference;
 
-      new_end = g_date_time_add_days (dnd_date, 1);
+      difference = g_date_time_difference (end_date, start_date);
+      difference /= G_TIME_SPAN_HOUR;
 
+      new_end = g_date_time_add_hours (dnd_date, difference);
       gcal_event_set_date_end (event, new_end);
     }
 
+  /*
+   * Set the start date ~after~ the end date, so we can compare
+   * the event's start and end dates above
+   */
+  gcal_event_set_date_start (event, dnd_date);
+
   /* Commit the changes */
   gcal_manager_update_event (self->manager, event);