From b1863cff1dc97cb1eafcad70906b684a71029405 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lubo=C5=A1=20Dole=C5=BEel?= <lubos@dolezel.info>
Date: Sat, 8 Jun 2013 19:02:10 +0000
Subject: [PATCH] * Source/NSTimeZone.m   Implement
 nextDaylightSavingTimeTransitionAfterDate:

git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@36709 72102866-910b-0410-8b05-ffd578937521
---
 ChangeLog                   |  5 +++
 Source/NSTimeZone.m         | 67 +++++++++++++++++++++++++++++++++++++
 Tests/base/NSTimeZone/use.m |  6 ++++
 3 files changed, 78 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 11261c24c..493840420 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2013-06-08 Lubos Dolezel <lubos@dolezel.info>
+
+	* Source/NSTimeZone.m
+	  Implement nextDaylightSavingTimeTransitionAfterDate:
+
 2013-06-06 Sebastian Reitenbach <sebastia@l00-bugdead-prods.de>
 
 	* Source/Additions/Unicode.m
diff --git a/Source/NSTimeZone.m b/Source/NSTimeZone.m
index 28ac99c15..fc4ba644d 100644
--- a/Source/NSTimeZone.m
+++ b/Source/NSTimeZone.m
@@ -166,6 +166,7 @@ NSString * const NSSystemTimeZoneDidChangeNotification
 #endif
 
 #define BUFFER_SIZE 512
+#define WEEK_MILLISECONDS (7.0*24.0*60.0*60.0*1000.0)
 
 #if GS_USE_ICU == 1
 static inline int
@@ -2231,7 +2232,73 @@ localZoneString, [zone name], sign, s/3600, (s/60)%60);
 
 - (NSDate *) nextDaylightSavingTimeTransitionAfterDate: (NSDate *)aDate
 {
+#if GS_USE_ICU == 1
+  /* ICU doesn't provide transition information per se.
+   * The canonical method of retrieving this piece of information is to
+   * use binary search.
+   */
+  
+  int32_t originalOffset, currentOffset;
+  UCalendar *cal;
+  UErrorCode err = U_ZERO_ERROR;
+  UDate currentTime;
+  int i;
+  NSDate* result = nil;
+  
+  cal = ICUCalendarSetup (self, nil);
+  if (cal == NULL)
+    return nil;
+  
+  currentTime = [aDate timeIntervalSince1970] * 1000.0;
+  ucal_setMillis (cal, currentTime, &err);
+  originalOffset = ucal_get (cal, UCAL_DST_OFFSET, &err);
+  if (U_FAILURE(err))
+    return nil;
+
+  /* First try to find the next transition by adding a week at a time */
+  /* Avoid ending in an infinite loop in case there is no transition at all */
+
+  for (i = 0; i < 53; i++)
+    {
+      /* Add a single week */
+      currentTime += WEEK_MILLISECONDS;
+
+	  ucal_setMillis (cal, currentTime, &err);
+	  if (U_FAILURE(err))
+        break;
+
+	  currentOffset = ucal_get (cal, UCAL_DST_OFFSET, &err);
+	  if (U_FAILURE(err))
+        break;
+
+	  if (currentOffset != originalOffset)
+        {
+          double interval = WEEK_MILLISECONDS / 2.0;
+          /* Now use bisection to determine the exact moment */
+
+		  while (interval >= 1.0)
+            {
+              ucal_setMillis (cal, currentTime - interval, &err);
+
+              currentOffset = ucal_get (cal, UCAL_DST_OFFSET, &err);
+
+              if (currentOffset != originalOffset)
+                currentTime -= interval; /* it is in the lower half */
+
+              interval /= 2.0;
+            }
+
+           result =
+             [NSDate dateWithTimeIntervalSince1970: floor(currentTime/1000.0)];
+        }
+    }
+
+  ucal_close (cal);
+  
+  return result;
+#else
   return nil;   // FIXME;
+#endif
 }
 
 - (NSTimeInterval) daylightSavingTimeOffset
diff --git a/Tests/base/NSTimeZone/use.m b/Tests/base/NSTimeZone/use.m
index b2b17d44d..0199bbbcd 100644
--- a/Tests/base/NSTimeZone/use.m
+++ b/Tests/base/NSTimeZone/use.m
@@ -50,6 +50,12 @@ int main()
        && [current isDaylightSavingTime] == NO,
        "can set default time zone");
   
+  current = [NSTimeZone timeZoneWithName: @"Europe/Brussels"];
+  date = [current nextDaylightSavingTimeTransitionAfterDate:
+    [NSDate dateWithString: @"2013-06-08 20:00:00 +0200"]];
+  PASS_EQUAL(date, [NSDate dateWithString: @"2013-10-27 03:00:00 +0200"],
+    "can calculate next DST transition");
+  
   START_SET("NSLocale")
   if (!NSLOCALE_SUPPORTED)
     SKIP("NSLocale not supported\nThe ICU library was not available when GNUstep-base was built")