[corlib] Added to TimeZoneInfo method GetDaylightChanges.

TimeZoneInfo.GetDaylightChanges returns DaylightTime from AdjustmentRules but when those are not available it is also able to do it from transitions.

diff --git a/mcs/class/corlib/System/TimeZoneInfo.cs b/mcs/class/corlib/System/TimeZoneInfo.cs
index aa93584c933c92e8461a9929723304005038acf9..a61f048476015f52cae0657687f4ca9eb62f3d6f 100644 (file)
--- a/mcs/class/corlib/System/TimeZoneInfo.cs
+++ b/mcs/class/corlib/System/TimeZoneInfo.cs
@@ -880,6 +880,68 @@ namespace System
                        throw new NotImplementedException ();
                }
 
+               internal DaylightTime GetDaylightChanges (int year)
+               {
+                       DateTime start = DateTime.MinValue, end = DateTime.MinValue;
+                       TimeSpan delta = new TimeSpan ();
+
+                       if (transitions != null) {
+                               end = DateTime.MaxValue;
+                               for (var i =  transitions.Count - 1; i >= 0; i--) {
+                                       var pair = transitions [i];
+                                       DateTime ttime = pair.Key;
+                                       TimeType ttype = pair.Value;
+
+                                       if (ttype.IsDst) {
+                                               // DaylightTime.Delta is relative to the current BaseUtcOffset.
+                                               var d =  new TimeSpan (0, 0, ttype.Offset) - BaseUtcOffset;
+                                               // Handle DST gradients
+                                               if (start != DateTime.MinValue && delta != d)
+                                                       end = start;
+
+                                               start = ttime;
+                                               delta = d;
+
+                                               if (ttime.Year <= year)
+                                                       break;
+                                       } else {
+                                               if (ttime.Year < year)
+                                                       break;
+
+                                               end = ttime;
+                                               start = DateTime.MinValue;
+                                       }
+                               }
+
+                               // DaylightTime.Start is relative to the Standard time.
+                               if (start != DateTime.MinValue)
+                                       start += BaseUtcOffset;
+
+                               // DaylightTime.End is relative to the DST time.
+                               if (end != DateTime.MaxValue)
+                                       end += BaseUtcOffset + delta;
+                       } else {
+                               AdjustmentRule rule = null;
+                               foreach (var r in GetAdjustmentRules ()) {
+                                       if (r.DateEnd.Year < year)
+                                               continue;
+                                       if (r.DateStart.Year > year)
+                                               break;
+                                       rule = r;
+                               }
+                               if (rule != null) {
+                                       start = TransitionPoint (rule.DaylightTransitionStart, year);
+                                       end = TransitionPoint (rule.DaylightTransitionEnd, year);
+                                       delta = rule.DaylightDelta;
+                               }
+                       }
+
+                       if (start == DateTime.MinValue || end == DateTime.MinValue)
+                               return new DaylightTime (new DateTime (), new DateTime (), new TimeSpan ());
+
+                       return new DaylightTime (start, end, delta);
+               }
+
                public bool IsInvalidTime (DateTime dateTime)
                {
                        if (dateTime.Kind == DateTimeKind.Utc)