1 files changed, 147 insertions, 0 deletions
diff --git a/thirdparty/icu4c/common/wintz.cpp b/thirdparty/icu4c/common/wintz.cpp
new file mode 100644
index 0000000000..3730232286
--- /dev/null
+++ b/thirdparty/icu4c/common/wintz.cpp
@@ -0,0 +1,147 @@
+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+********************************************************************************
+*   Copyright (C) 2005-2015, International Business Machines
+*   Corporation and others.  All Rights Reserved.
+********************************************************************************
+*
+* File WINTZ.CPP
+*
+********************************************************************************
+*/
+
+#include "unicode/utypes.h"
+
+#if U_PLATFORM_USES_ONLY_WIN32_API
+
+#include "wintz.h"
+#include "charstr.h"
+#include "cmemory.h"
+#include "cstring.h"
+
+#include "unicode/ures.h"
+#include "unicode/unistr.h"
+#include "uresimp.h"
+
+#ifndef WIN32_LEAN_AND_MEAN
+#   define WIN32_LEAN_AND_MEAN
+#endif
+#   define VC_EXTRALEAN
+#   define NOUSER
+#   define NOSERVICE
+#   define NOIME
+#   define NOMCX
+#include <windows.h>
+
+U_NAMESPACE_BEGIN
+
+/**
+* Main Windows time zone detection function.
+* Returns the Windows time zone converted to an ICU time zone as a heap-allocated buffer, or nullptr upon failure.
+*
+* Note: We use the Win32 API GetDynamicTimeZoneInformation (available since Vista+) to get the current time zone info.
+* This API returns a non-localized time zone name, which is mapped to an ICU time zone ID (~ Olsen ID).
+*/
+U_CAPI const char* U_EXPORT2
+uprv_detectWindowsTimeZone()
+{
+    // Obtain the DYNAMIC_TIME_ZONE_INFORMATION info to get the non-localized time zone name.
+    DYNAMIC_TIME_ZONE_INFORMATION dynamicTZI;
+    uprv_memset(&dynamicTZI, 0, sizeof(dynamicTZI));
+    SYSTEMTIME systemTimeAllZero;
+    uprv_memset(&systemTimeAllZero, 0, sizeof(systemTimeAllZero));
+
+    if (GetDynamicTimeZoneInformation(&dynamicTZI) == TIME_ZONE_ID_INVALID) {
+        return nullptr;
+    }
+
+    // If the DST setting has been turned off in the Control Panel, then return "Etc/GMT<offset>".
+    //
+    // Note: This logic is based on how the Control Panel itself determines if DST is 'off' on Windows.
+    // The code is somewhat convoluted; in a sort of pseudo-code it looks like this:
+    // 
+    //   IF (GetDynamicTimeZoneInformation != TIME_ZONE_ID_INVALID) && (DynamicDaylightTimeDisabled != 0) &&
+    //      (StandardDate == DaylightDate) &&
+    //      (
+    //       (TimeZoneKeyName != Empty && StandardDate == 0) ||
+    //       (TimeZoneKeyName == Empty && StandardDate != 0)
+    //      )
+    //   THEN
+    //     DST setting is "Disabled".
+    //
+    if (dynamicTZI.DynamicDaylightTimeDisabled != 0 &&
+        uprv_memcmp(&dynamicTZI.StandardDate, &dynamicTZI.DaylightDate, sizeof(dynamicTZI.StandardDate)) == 0 &&
+        ((dynamicTZI.TimeZoneKeyName[0] != L'\0' && uprv_memcmp(&dynamicTZI.StandardDate, &systemTimeAllZero, sizeof(systemTimeAllZero)) == 0) ||
+         (dynamicTZI.TimeZoneKeyName[0] == L'\0' && uprv_memcmp(&dynamicTZI.StandardDate, &systemTimeAllZero, sizeof(systemTimeAllZero)) != 0)))
+    {
+        LONG utcOffsetMins = dynamicTZI.Bias;
+        if (utcOffsetMins == 0) {
+            return uprv_strdup("Etc/UTC");
+        }
+
+        // No way to support when DST is turned off and the offset in minutes is not a multiple of 60.
+        if (utcOffsetMins % 60 == 0) {
+            char gmtOffsetTz[11] = {}; // "Etc/GMT+dd" is 11-char long with a terminal null.
+            // Note '-' before 'utcOffsetMin'. The timezone ID's sign convention
+            // is that a timezone ahead of UTC is Etc/GMT-<offset> and a timezone
+            // behind UTC is Etc/GMT+<offset>.
+            int ret = snprintf(gmtOffsetTz, UPRV_LENGTHOF(gmtOffsetTz), "Etc/GMT%+d", -utcOffsetMins / 60);
+            if (ret > 0 && ret < UPRV_LENGTHOF(gmtOffsetTz)) {
+                return uprv_strdup(gmtOffsetTz);
+            }
+        }
+    }
+
+    // If DST is NOT disabled, but we have an empty TimeZoneKeyName, then it is unclear
+    // what we should do as this should not happen.
+    if (dynamicTZI.TimeZoneKeyName[0] == 0) {
+        return nullptr;
+    }
+
+    CharString winTZ;
+    UErrorCode status = U_ZERO_ERROR;
+    winTZ.appendInvariantChars(UnicodeString(TRUE, dynamicTZI.TimeZoneKeyName, -1), status);
+
+    // Map Windows Timezone name (non-localized) to ICU timezone ID (~ Olson timezone id).
+    StackUResourceBundle winTZBundle;
+    ures_openDirectFillIn(winTZBundle.getAlias(), nullptr, "windowsZones", &status);
+    ures_getByKey(winTZBundle.getAlias(), "mapTimezones", winTZBundle.getAlias(), &status);
+    ures_getByKey(winTZBundle.getAlias(), winTZ.data(), winTZBundle.getAlias(), &status);
+
+    if (U_FAILURE(status)) {
+        return nullptr;
+    }
+    
+    // Note: Since the ISO 3166 country/region codes are all invariant ASCII chars, we can
+    // directly downcast from wchar_t to do the conversion.
+    // We could call the A version of the GetGeoInfo API, but that would be slightly slower than calling the W API,
+    // as the A version of the API will end up calling MultiByteToWideChar anyways internally.
+    wchar_t regionCodeW[3] = {};
+    char regionCode[3] = {}; // 2 letter ISO 3166 country/region code made entirely of invariant chars.
+    int geoId = GetUserGeoID(GEOCLASS_NATION);
+    int regionCodeLen = GetGeoInfoW(geoId, GEO_ISO2, regionCodeW, UPRV_LENGTHOF(regionCodeW), 0);
+
+    const UChar *icuTZ16 = nullptr;
+    int32_t tzLen;
+
+    if (regionCodeLen != 0) {
+        for (int i = 0; i < UPRV_LENGTHOF(regionCodeW); i++) {
+            regionCode[i] = static_cast<char>(regionCodeW[i]);
+        }
+        icuTZ16 = ures_getStringByKey(winTZBundle.getAlias(), regionCode, &tzLen, &status);
+    }
+    if (regionCodeLen == 0 || U_FAILURE(status)) {
+        // fallback to default "001" (world)
+        status = U_ZERO_ERROR;
+        icuTZ16 = ures_getStringByKey(winTZBundle.getAlias(), "001", &tzLen, &status);
+    }
+
+    // Note: cloneData returns nullptr if the status is a failure, so this
+    // will return nullptr if the above look-up fails.
+    CharString icuTZStr;
+    return icuTZStr.appendInvariantChars(icuTZ16, tzLen, status).cloneData(status);
+}
+
+U_NAMESPACE_END
+#endif /* U_PLATFORM_USES_ONLY_WIN32_API  */