/*
********************************************************************************
*   Copyright (C) 2005-2008, International Business Machines
*   Corporation and others.  All Rights Reserved.
********************************************************************************
*
* File WINTZ.CPP
*
********************************************************************************
*/

#include "unicode/utypes.h"

#ifdef U_WINDOWS

#include "wintz.h"

#include "cmemory.h"
#include "cstring.h"

#include "unicode/ustring.h"
#include "unicode/ures.h"

#   define WIN32_LEAN_AND_MEAN
#   define VC_EXTRALEAN
#   define NOUSER
#   define NOSERVICE
#   define NOIME
#   define NOMCX
#include <windows.h>

/* The layout of the Tzi value in the registry */
typedef struct
{
    int32_t bias;
    int32_t standardBias;
    int32_t daylightBias;
    SYSTEMTIME standardDate;
    SYSTEMTIME daylightDate;
} TZI;

/**
 * Various registry keys and key fragments.
 */
static const char CURRENT_ZONE_REGKEY[] = "SYSTEM\\CurrentControlSet\\Control\\TimeZoneInformation\\";
static const char STANDARD_NAME_REGKEY[] = "StandardName";
static const char STANDARD_TIME_REGKEY[] = " Standard Time";
static const char TZI_REGKEY[] = "TZI";
static const char STD_REGKEY[] = "Std";

/**
 * HKLM subkeys used to probe for the flavor of Windows.  Note that we
 * specifically check for the "GMT" zone subkey; this is present on
 * NT, but on XP has become "GMT Standard Time".  We need to
 * discriminate between these cases.
 */
static const char* const WIN_TYPE_PROBE_REGKEY[] = {
    /* WIN_9X_ME_TYPE */
    "SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Time Zones",

    /* WIN_NT_TYPE */
    "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones\\GMT"

    /* otherwise: WIN_2K_XP_TYPE */
};

/**
 * The time zone root subkeys (under HKLM) for different flavors of
 * Windows.
 */
static const char* const TZ_REGKEY[] = {
    /* WIN_9X_ME_TYPE */
    "SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Time Zones\\",

    /* WIN_NT_TYPE | WIN_2K_XP_TYPE */
    "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Time Zones\\"
};

/**
 * Flavor of Windows, from our perspective.  Not a real OS version,
 * but rather the flavor of the layout of the time zone information in
 * the registry.
 */
enum {
    WIN_9X_ME_TYPE = 1,
    WIN_NT_TYPE = 2,
    WIN_2K_XP_TYPE = 3
};

static int32_t gWinType = 0;

static int32_t detectWindowsType()
{
    int32_t winType;
    LONG result;
    HKEY hkey;

    /* Detect the version of windows by trying to open a sequence of
        probe keys.  We don't use the OS version API because what we
        really want to know is how the registry is laid out.
        Specifically, is it 9x/Me or not, and is it "GMT" or "GMT
        Standard Time". */
    for (winType = 0; winType < 2; winType++) {
        result = RegOpenKeyExA(HKEY_LOCAL_MACHINE,
                              WIN_TYPE_PROBE_REGKEY[winType],
                              0,
                              KEY_QUERY_VALUE,
                              &hkey);
        RegCloseKey(hkey);

        if (result == ERROR_SUCCESS) {
            break;
        }
    }

    return winType+1; // +1 to bring it inline with the enum
}

static LONG openTZRegKey(HKEY *hkey, const char *winid)
{
    char subKeyName[110]; /* TODO: why 96?? */
    char *name;
    LONG result;

    /* This isn't thread safe, but it's good enough because the result should be constant per system. */
    if (gWinType <= 0) {
        gWinType = detectWindowsType();
    }

    uprv_strcpy(subKeyName, TZ_REGKEY[(gWinType != WIN_9X_ME_TYPE)]);
    name = &subKeyName[strlen(subKeyName)];
    uprv_strcat(subKeyName, winid);

    if (gWinType == WIN_9X_ME_TYPE) {
        /* Remove " Standard Time" */
        char *pStd = uprv_strstr(subKeyName, STANDARD_TIME_REGKEY);
        if (pStd) {
            *pStd = 0;
        }
    }

    result = RegOpenKeyExA(HKEY_LOCAL_MACHINE,
                            subKeyName,
                            0,
                            KEY_QUERY_VALUE,
                            hkey);
    return result;
}

static LONG getTZI(const char *winid, TZI *tzi)
{
    DWORD cbData = sizeof(TZI);
    LONG result;
    HKEY hkey;

    result = openTZRegKey(&hkey, winid);

    if (result == ERROR_SUCCESS) {
        result = RegQueryValueExA(hkey,
                                    TZI_REGKEY,
                                    NULL,
                                    NULL,
                                    (LPBYTE)tzi,
                                    &cbData);

    }

    RegCloseKey(hkey);

    return result;
}

/*
  This code attempts to detect the Windows time zone, as set in the
  Windows Date and Time control panel.  It attempts to work on
  multiple flavors of Windows (9x, Me, NT, 2000, XP) and on localized
  installs.  It works by directly interrogating the registry and
  comparing the data there with the data returned by the
  GetTimeZoneInformation API, along with some other strategies.  The
  registry contains time zone data under one of two keys (depending on
  the flavor of Windows):

    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Time Zones\
    HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones\

  Under this key are several subkeys, one for each time zone.  These
  subkeys are named "Pacific" on Win9x/Me and "Pacific Standard Time"
  on WinNT/2k/XP.  There are some other wrinkles; see the code for
  details.  The subkey name is NOT LOCALIZED, allowing us to support
  localized installs.

  Under the subkey are data values.  We care about:

    Std   Standard time display name, localized
    TZI   Binary block of data

  The TZI data is of particular interest.  It contains the offset, two
  more offsets for standard and daylight time, and the start and end
  rules.  This is the same data returned by the GetTimeZoneInformation
  API.  The API may modify the data on the way out, so we have to be
  careful, but essentially we do a binary comparison against the TZI
  blocks of various registry keys.  When we find a match, we know what
  time zone Windows is set to.  Since the registry key is not
  localized, we can then translate the key through a simple table
  lookup into the corresponding ICU time zone.

  This strategy doesn't always work because there are zones which
  share an offset and rules, so more than one TZI block will match.
  For example, both Tokyo and Seoul are at GMT+9 with no DST rules;
  their TZI blocks are identical.  For these cases, we fall back to a
  name lookup.  We attempt to match the display name as stored in the
  registry for the current zone to the display name stored in the
  registry for various Windows zones.  By comparing the registry data
  directly we avoid conversion complications.

  Author: Alan Liu
  Since: ICU 2.6
  Based on original code by Carl Brown <cbrown@xnetinc.com>
*/

/**
 * Main Windows time zone detection function.  Returns the Windows
 * time zone, translated to an ICU time zone, or NULL upon failure.
 */
U_CFUNC const char* U_EXPORT2
uprv_detectWindowsTimeZone() {
    UErrorCode status = U_ZERO_ERROR;
    UResourceBundle* bundle = NULL;
    char* icuid = NULL;

    LONG result;
    TZI tziKey;
    TZI tziReg;
    TIME_ZONE_INFORMATION apiTZI;

    /* Obtain TIME_ZONE_INFORMATION from the API, and then convert it
       to TZI.  We could also interrogate the registry directly; we do
       this below if needed. */
    uprv_memset(&apiTZI, 0, sizeof(apiTZI));
    uprv_memset(&tziKey, 0, sizeof(tziKey));
    uprv_memset(&tziReg, 0, sizeof(tziReg));
    GetTimeZoneInformation(&apiTZI);
    tziKey.bias = apiTZI.Bias;
    uprv_memcpy((char *)&tziKey.standardDate, (char*)&apiTZI.StandardDate,
           sizeof(apiTZI.StandardDate));
    uprv_memcpy((char *)&tziKey.daylightDate, (char*)&apiTZI.DaylightDate,
           sizeof(apiTZI.DaylightDate));

    bundle = ures_openDirect(NULL, "supplementalData", &status);
    bundle = ures_getByKey(bundle, "mapTimezones", bundle, &status);
    bundle = ures_getByKey(bundle, "windows", bundle, &status);

    /* Note: We get the winid not from static tables but from resource bundle. */
    while (U_SUCCESS(status) && ures_hasNext(bundle)) {
        const char* winid;
        int32_t len;
        UResourceBundle* winTZ = ures_getNextResource(bundle, NULL, &status);
        if (U_FAILURE(status)) {
            break;
        }
        winid = ures_getKey(winTZ);
        result = getTZI(winid, &tziReg);

        if (result == ERROR_SUCCESS) {
            /* Windows alters the DaylightBias in some situations.
               Using the bias and the rules suffices, so overwrite
               these unreliable fields. */
            tziKey.standardBias = tziReg.standardBias;
            tziKey.daylightBias = tziReg.daylightBias;

            if (uprv_memcmp((char *)&tziKey, (char*)&tziReg, sizeof(tziKey)) == 0) {
                const UChar* icuTZ = ures_getString(winTZ, &len, &status);
                if (U_SUCCESS(status)) {
                    icuid = (char*)uprv_malloc(sizeof(char) * (len + 1));
                    uprv_memset(icuid, 0, len + 1);
                    u_austrncpy(icuid, icuTZ, len);
                }
            }
        }
        ures_close(winTZ);
        if (icuid != NULL) {
            break;
        }
    }

    ures_close(bundle);

    return icuid;
}

#endif /* #ifdef U_WINDOWS */