[california] Properly adjust start/end date when RRULE updated

[Jim Nelson <jnelson src gnome org>]

commit 39482e8216e6b7a88da61e217216eba45c6ac9d1
Author: Jim Nelson <jim yorba org>
Date:   Wed Sep 24 15:23:35 2014 -0700

    Properly adjust start/end date when RRULE updated

 src/component/component-event.vala         |   17 +++++++++++++----
 src/host/host-create-update-recurring.vala |    6 +++---
 2 files changed, 16 insertions(+), 7 deletions(-)
---
diff --git a/src/component/component-event.vala b/src/component/component-event.vala
index ed3e2ed..1ead71e 100644
--- a/src/component/component-event.vala
+++ b/src/component/component-event.vala
@@ -294,22 +294,31 @@ public class Event : Instance, Gee.Comparable<Event> {
      * { link set_event_exact_time_span} but without the hassle of preserving start and end times
      * while changing the dates.
      */
-    public void adjust_event_date_span(Calendar.DateSpan date_span) {
+    public void adjust_start_date(Calendar.Date new_start_date) {
+        // generate a new end date that is the same chronological distance from the original start
+        // date
+        Calendar.DateSpan orig_dates = get_event_date_span(null);
+        int diff = orig_dates.start_date.difference(new_start_date);
+        if (diff == 0)
+            return;
+        
+        Calendar.Date new_end_date = orig_dates.end_date.adjust(diff);
+        
         if (is_all_day) {
-            set_event_date_span(date_span);
+            set_event_date_span(new Calendar.DateSpan(new_start_date, new_end_date));
             
             return;
         }
         
         Calendar.ExactTime new_start_time = new Calendar.ExactTime(
             exact_time_span.start_exact_time.tz,
-            date_span.start_date,
+            new_start_date,
             exact_time_span.start_exact_time.to_wall_time()
         );
         
         Calendar.ExactTime new_end_time = new Calendar.ExactTime(
             exact_time_span.end_exact_time.tz,
-            date_span.end_date,
+            new_end_date,
             exact_time_span.end_exact_time.to_wall_time()
         );
         
diff --git a/src/host/host-create-update-recurring.vala b/src/host/host-create-update-recurring.vala
index 86ab149..a81b7fa 100644
--- a/src/host/host-create-update-recurring.vala
+++ b/src/host/host-create-update-recurring.vala
@@ -571,15 +571,15 @@ public class CreateUpdateRecurring : Gtk.Grid, Toolkit.Card {
         // set start and end dates (which may actually be date-times, so use adjust)
         if (never_radiobutton.active) {
             // no duration
-            master.adjust_event_date_span(start_date.to_date_span());
+            master.adjust_start_date(start_date);
             rrule.set_recurrence_end_date(null);
         } else if (ends_on_radiobutton.active) {
-            master.adjust_event_date_span(new Calendar.DateSpan(start_date, end_date));
+            master.adjust_start_date(start_date);
             rrule.set_recurrence_end_date(end_date);
         } else {
             assert(after_radiobutton.active);
             
-            master.adjust_event_date_span(start_date.to_date_span());
+            master.adjust_start_date(start_date);
             rrule.set_recurrence_count(Numeric.floor_int(int.parse(after_entry.text), 1));
         }