# This code was originally contributed by Jeffrey Harris.
import datetime
import struct
import winreg


__all__ = ["tzwin", "tzwinlocal"]

ONEWEEK = datetime.timedelta(7)

TZKEYNAMENT = r"SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones"
TZKEYNAME9X = r"SOFTWARE\Microsoft\Windows\CurrentVersion\Time Zones"
TZLOCALKEYNAME = r"SYSTEM\CurrentControlSet\Control\TimeZoneInformation"

def _settzkeyname():
    global TZKEYNAME
    handle = winreg.ConnectRegistry(None, winreg.HKEY_LOCAL_MACHINE)
    try:
        winreg.OpenKey(handle, TZKEYNAMENT).Close()
        TZKEYNAME = TZKEYNAMENT
    except WindowsError:
        TZKEYNAME = TZKEYNAME9X
    handle.Close()

_settzkeyname()

class tzwinbase(datetime.tzinfo):
    """tzinfo class based on win32's timezones available in the registry."""

    def utcoffset(self, dt):
        if self._isdst(dt):
            return datetime.timedelta(minutes=self._dstoffset)
        else:
            return datetime.timedelta(minutes=self._stdoffset)

    def dst(self, dt):
        if self._isdst(dt):
            minutes = self._dstoffset - self._stdoffset
            return datetime.timedelta(minutes=minutes)
        else:
            return datetime.timedelta(0)
        
    def tzname(self, dt):
        if self._isdst(dt):
            return self._dstname
        else:
            return self._stdname

    def list():
        """Return a list of all time zones known to the system."""
        handle = winreg.ConnectRegistry(None, winreg.HKEY_LOCAL_MACHINE)
        tzkey = winreg.OpenKey(handle, TZKEYNAME)
        result = [winreg.EnumKey(tzkey, i)
                  for i in range(winreg.QueryInfoKey(tzkey)[0])]
        tzkey.Close()
        handle.Close()
        return result
    list = staticmethod(list)

    def display(self):
        return self._display
    
    def _isdst(self, dt):
        dston = picknthweekday(dt.year, self._dstmonth, self._dstdayofweek,
                               self._dsthour, self._dstminute,
                               self._dstweeknumber)
        dstoff = picknthweekday(dt.year, self._stdmonth, self._stddayofweek,
                                self._stdhour, self._stdminute,
                                self._stdweeknumber)
        if dston < dstoff:
            return dston <= dt.replace(tzinfo=None) < dstoff
        else:
            return not dstoff <= dt.replace(tzinfo=None) < dston


class tzwin(tzwinbase):

    def __init__(self, name):
        self._name = name

        handle = winreg.ConnectRegistry(None, winreg.HKEY_LOCAL_MACHINE)
        tzkey = winreg.OpenKey(handle, "%s\%s" % (TZKEYNAME, name))
        keydict = valuestodict(tzkey)
        tzkey.Close()
        handle.Close()

        self._stdname = keydict["Std"].encode("iso-8859-1")
        self._dstname = keydict["Dlt"].encode("iso-8859-1")

        self._display = keydict["Display"]
        
        # See http://ww_winreg.jsiinc.com/SUBA/tip0300/rh0398.htm
        tup = struct.unpack("=3l16h", keydict["TZI"])
        self._stdoffset = -tup[0]-tup[1]         # Bias + StandardBias * -1
        self._dstoffset = self._stdoffset-tup[2] # + DaylightBias * -1
        
        (self._stdmonth,
         self._stddayofweek,  # Sunday = 0
         self._stdweeknumber, # Last = 5
         self._stdhour,
         self._stdminute) = tup[4:9]

        (self._dstmonth,
         self._dstdayofweek,  # Sunday = 0
         self._dstweeknumber, # Last = 5
         self._dsthour,
         self._dstminute) = tup[12:17]

    def __repr__(self):
        return "tzwin(%s)" % repr(self._name)

    def __reduce__(self):
        return (self.__class__, (self._name,))


class tzwinlocal(tzwinbase):
    
    def __init__(self):

        handle = winreg.ConnectRegistry(None, winreg.HKEY_LOCAL_MACHINE)

        tzlocalkey = winreg.OpenKey(handle, TZLOCALKEYNAME)
        keydict = valuestodict(tzlocalkey)
        tzlocalkey.Close()

        self._stdname = keydict["StandardName"].encode("iso-8859-1")
        self._dstname = keydict["DaylightName"].encode("iso-8859-1")

        try:
            tzkey = winreg.OpenKey(handle, "%s\%s"%(TZKEYNAME, self._stdname))
            _keydict = valuestodict(tzkey)
            self._display = _keydict["Display"]
            tzkey.Close()
        except OSError:
            self._display = None

        handle.Close()
        
        self._stdoffset = -keydict["Bias"]-keydict["StandardBias"]
        self._dstoffset = self._stdoffset-keydict["DaylightBias"]


        # See http://ww_winreg.jsiinc.com/SUBA/tip0300/rh0398.htm
        tup = struct.unpack("=8h", keydict["StandardStart"])

        (self._stdmonth,
         self._stddayofweek,  # Sunday = 0
         self._stdweeknumber, # Last = 5
         self._stdhour,
         self._stdminute) = tup[1:6]

        tup = struct.unpack("=8h", keydict["DaylightStart"])

        (self._dstmonth,
         self._dstdayofweek,  # Sunday = 0
         self._dstweeknumber, # Last = 5
         self._dsthour,
         self._dstminute) = tup[1:6]

    def __reduce__(self):
        return (self.__class__, ())

def picknthweekday(year, month, dayofweek, hour, minute, whichweek):
    """dayofweek == 0 means Sunday, whichweek 5 means last instance"""
    first = datetime.datetime(year, month, 1, hour, minute)
    weekdayone = first.replace(day=((dayofweek-first.isoweekday())%7+1))
    for n in range(whichweek):
        dt = weekdayone+(whichweek-n)*ONEWEEK
        if dt.month == month:
            return dt

def valuestodict(key):
    """Convert a registry key's values to a dictionary."""
    dict = {}
    size = winreg.QueryInfoKey(key)[1]
    for i in range(size):
        data = winreg.EnumValue(key, i)
        dict[data[0]] = data[1]
    return dict