import re

_ISO8601_DURATION_RE = re.compile(
    r"P(?:(?P<days>\d+)D)?"
    r"(?:T(?:(?P<hours>\d+)H)?(?:(?P<minutes>\d+)M)?(?:(?P<seconds>\d+)S)?)?"
)


def parse_iso8601_duration(value: str | None) -> int | None:
    if not value:
        return None
    match = _ISO8601_DURATION_RE.fullmatch(value)
    if not match:
        return None
    parts = match.groupdict()
    if not any(parts.values()):
        return None
    days = int(parts["days"] or 0)
    hours = int(parts["hours"] or 0)
    minutes = int(parts["minutes"] or 0)
    seconds = int(parts["seconds"] or 0)
    return days * 86400 + hours * 3600 + minutes * 60 + seconds