fix daylight time in QTimeZone on Android

Android does not provide an API to access daylight time transitions,
so the standard QTimeZonePrivate::dataForLocalTime only returns
standard time without the daylight offset

Therefore provide an override,
QAndroidTimeZonePrivate::dataForLocalTime, which tests daylight time
offsets directly rather than using transitions.

Change-Id: Ia8adaf9af40da38aadfa7d22d9a3fe9da9ba24a8
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

src/corelib/tools/qtimezoneprivate_android.cpp

@@ -201,6 +201,58 @@ QTimeZonePrivate::Data QAndroidTimeZonePrivate::previousTransition(qint64 before
     return invalidData();
 }
 
+// Since Android does not provide an API to access transitions,
+// dataForLocalTime needs to be reimplemented without direct use of transitions
+QTimeZonePrivate::Data QAndroidTimeZonePrivate::dataForLocalTime(qint64 forLocalMSecs) const
+{
+    if (!androidTimeZone.isValid()) {
+        return invalidData();
+    } else {
+        qint64 UTCepochMSecs;
+
+        // compare the UTC time with standard offset against normal daylight offset of one hour
+        qint64 standardUTCMSecs(forLocalMSecs - (standardTimeOffset(forLocalMSecs) * 1000));
+        qint64 daylightUTCMsecs;
+
+        // Check if daylight time does apply,
+        // checking also for daylight time boundaries
+        if (isDaylightTime(standardUTCMSecs)) {
+            // If daylight does apply, then standardUTCMSecs will be an hour or so ahead of the real epoch time
+            // so check that time
+            daylightUTCMsecs = standardUTCMSecs - daylightTimeOffset(standardUTCMSecs)*1000;
+            if (isDaylightTime(daylightUTCMsecs)) {
+                // daylight time confirmed
+                UTCepochMSecs = daylightUTCMsecs;
+            } else {
+                // daylight time has just finished
+                UTCepochMSecs = standardUTCMSecs;
+            }
+        } else {
+            // Standard time indicated, but check for a false negative.
+            // Would a standard one-hour daylight offset indicate daylight time?
+            daylightUTCMsecs = standardUTCMSecs - 3600000; // 3600000 MSECS_PER_HOUR
+            if (isDaylightTime(daylightUTCMsecs)) {
+                // daylight time may have just started,
+                // but double check against timezone's own daylight offset
+                // (don't necessarily assume a one-hour offset)
+                daylightUTCMsecs = standardUTCMSecs - daylightTimeOffset(daylightUTCMsecs)*1000;
+                if (isDaylightTime(daylightUTCMsecs)) {
+                    // daylight time confirmed
+                    UTCepochMSecs = daylightUTCMsecs;
+                } else {
+                    // false positive, apply standard time after all
+                    UTCepochMSecs = standardUTCMSecs;
+                }
+            } else {
+                // confirmed standard time
+                UTCepochMSecs = standardUTCMSecs;
+            }
+        }
+
+        return data(UTCepochMSecs);
+    }
+}
+
 QByteArray QAndroidTimeZonePrivate::systemTimeZoneId() const
 {
     QJNIObjectPrivate androidSystemTimeZone = QJNIObjectPrivate::callStaticObjectMethod("java.util.TimeZone", "getDefault", "()Ljava/util/TimeZone;");

src/corelib/tools/qtimezoneprivate_p.h

@@ -458,6 +458,8 @@ public:
     Data nextTransition(qint64 afterMSecsSinceEpoch) const Q_DECL_OVERRIDE;
     Data previousTransition(qint64 beforeMSecsSinceEpoch) const Q_DECL_OVERRIDE;
 
+    Data dataForLocalTime(qint64 forLocalMSecs) const Q_DECL_OVERRIDE;
+
     QByteArray systemTimeZoneId() const Q_DECL_OVERRIDE;
 
     QSet<QByteArray> availableTimeZoneIds() const Q_DECL_OVERRIDE;