[gnome-calendar] month-view: fix dnd

[Ernestas Kulik <ernestask src gnome org>]

commit b5fb1d4ec3155ba26b80f4d723cf1fffc80f62cd
Author: Ernestas Kulik <ernestask src gnome org>
Date:   Wed Aug 3 22:20:04 2016 +0300

    month-view: fix dnd
    
    Currently, the event is moved by a number of cells, calculated from the
    start date and the cell index. The problem with that is that it does not
    work with events, whose start and end dates of which are on different
    months or years. This commit changes the logic so that the start date is
    calculated by taking the year and month difference into consideration
    and the end date is set by adding the event length to the adjusted start
    date.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=769470

 src/gcal-month-view.c |   32 ++++++++++++++++++++++++++++----
 1 files changed, 28 insertions(+), 4 deletions(-)
---
diff --git a/src/gcal-month-view.c b/src/gcal-month-view.c
index 9194db9..5fd2b49 100644
--- a/src/gcal-month-view.c
+++ b/src/gcal-month-view.c
@@ -859,9 +859,12 @@ gcal_month_view_drag_drop (GtkWidget      *widget,
 {
   GcalMonthViewPrivate *priv = gcal_month_view_get_instance_private (GCAL_MONTH_VIEW (widget));
   GtkWidget *event_widget;
-  GDateTime *start_dt, *end_dt;
+  GDateTime *start_dt, *end_dt, *current_dt;
   GcalEvent *event;
   gint cell, diff;
+  gint start_month, current_month;
+  gint start_year, current_year;
+  GTimeSpan timespan;
 
   cell = get_dnd_cell (widget, x, y);
   event_widget = gtk_drag_get_source_widget (context);
@@ -871,9 +874,28 @@ gcal_month_view_drag_drop (GtkWidget      *widget,
   start_dt = gcal_event_get_date_start (event);
   end_dt = gcal_event_get_date_end (event);
 
-  diff = cell - priv->days_delay - g_date_time_get_day_of_month (start_dt) + 1;
+  start_month = g_date_time_get_month (start_dt);
+  start_year = g_date_time_get_year (start_dt);
+
+  current_dt = icaltime_to_datetime (priv->date);
+
+  current_month = g_date_time_get_month (current_dt);
+  current_year = g_date_time_get_year (current_dt);
+
+  g_clear_pointer (&current_dt, g_date_time_unref);
 
-  if (diff != 0)
+  if (end_dt)
+    timespan = g_date_time_difference (end_dt, start_dt);
+
+  start_dt = g_date_time_add_full (start_dt,
+                                   current_year - start_year,
+                                   current_month - start_month,
+                                   0, 0, 0, 0);
+
+  diff = cell - priv->days_delay - g_date_time_get_day_of_month (start_dt) + 1;
+  if (diff != 0 ||
+      current_month != start_month ||
+      current_year != start_year)
     {
       GDateTime *new_start = g_date_time_add_days (start_dt, diff);
 
@@ -882,7 +904,7 @@ gcal_month_view_drag_drop (GtkWidget      *widget,
       /* The event may have a NULL end date, so we have to check it here */
       if (end_dt)
         {
-          GDateTime *new_end = g_date_time_add_days (end_dt, diff);
+          GDateTime *new_end = g_date_time_add (new_start, timespan);
 
           gcal_event_set_date_end (event, new_end);
           g_clear_pointer (&new_end, g_date_time_unref);
@@ -893,6 +915,8 @@ gcal_month_view_drag_drop (GtkWidget      *widget,
       g_clear_pointer (&new_start, g_date_time_unref);
     }
 
+  g_clear_pointer (&start_dt, g_date_time_unref);
+
   /* Cancel the DnD */
   priv->dnd_cell = -1;
   gtk_drag_unhighlight (widget);