From b5fb1d4ec3155ba26b80f4d723cf1fffc80f62cd Mon Sep 17 00:00:00 2001
From: Ernestas Kulik <ernestask@src.gnome.org>
Date: Wed, 3 Aug 2016 22:20:04 +0300
Subject: [PATCH] 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 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/src/gcal-month-view.c b/src/gcal-month-view.c
index 9194db9f..5fd2b498 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);
 
-  if (diff != 0)
+  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 (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);