calculate dst offset with icu api

ucal_dst.py

# calculate dst offset with icu api
#
# /// script
# dependencies = ["win32more"]
# ///

from win32more import String
from win32more.Windows.Win32.Globalization import (
    UCAL_DEFAULT,
    UCAL_DST_OFFSET,
    UErrorCode,
    ucal_close,
    ucal_get,
    ucal_open,
    ucal_setDateTime,
)


def U_FAILURE(x):
    return x > 0


def ucal_dst(zone_id, year, month, day, hour, minute, second):
    status = UErrorCode()
    cal = ucal_open(String(zone_id), -1, None, UCAL_DEFAULT, status)
    if U_FAILURE(status.value):
        raise RuntimeError(status.value)
    ucal_setDateTime(cal, year, month, day, hour, minute, second, status)
    if U_FAILURE(status.value):
        raise RuntimeError(status.value)
    dst = ucal_get(cal, UCAL_DST_OFFSET, status)
    if U_FAILURE(status.value):
        raise RuntimeError(status.value)
    ucal_close(cal)
    return dst


assert ucal_dst("America/New_York", 2006, 1, 1, 12, 0, 0) == 0
assert ucal_dst("America/New_York", 2006, 5, 1, 12, 0, 0) == 3600000
assert ucal_dst("America/New_York", 1918, 3, 29, 8, 0, 0) == 3600000  # ?
assert ucal_dst("America/New_York", 1918, 3, 31, 8, 0, 0) == 3600000  # ?
assert ucal_dst("America/New_York", 1918, 4, 1, 8, 0, 0) == 3600000  # ?
assert ucal_dst("America/New_York", 1918, 4, 6, 8, 0, 0) == 3600000  # ?
assert ucal_dst("America/New_York", 1918, 4, 7, 8, 0, 0) == 3600000