def _email_address(block):
    if not isinstance(block,dict):
        return None,None
    inner=block.get("emailAddress") or block.get("email_address") or block
    if not isinstance(inner,dict):
        return None,None
    email=(inner.get("address") or inner.get("email") or "").strip() or None
    name=(inner.get("name") or "").strip() or None
    return email,name


def participants_from_event(payload):
    """Graph event dict -> (organizer, attendees) as {name, email} snapshots."""
    if not isinstance(payload,dict):
        payload={}
    org_email,org_name=_email_address(payload.get("organizer") or {})
    organizer=None
    if org_email or org_name:
        organizer={"name":org_name,"email":org_email}
    attendees=[]
    seen=set()
    for item in payload.get("attendees") or []:
        email,name=_email_address(item)
        key=(email or "").lower()
        if not email or key in seen:
            continue
        seen.add(key)
        attendees.append({"name":name,"email":email})
    return organizer,attendees


def serialize_event(payload) -> dict:
    """Upstream calendar event -> the fields the interview row stores."""
    if not isinstance(payload,dict):
        payload={}
    online=payload.get("onlineMeeting") or payload.get("online_meeting") or {}
    if not isinstance(online,dict):
        online={}
    start=payload.get("start")
    end=payload.get("end")
    if isinstance(start,dict):
        start=start.get("dateTime") or start.get("date_time")
    if isinstance(end,dict):
        end=end.get("dateTime") or end.get("date_time")
    if hasattr(start,"isoformat"):
        start=start.isoformat()
    if hasattr(end,"isoformat"):
        end=end.isoformat()
    event_id=payload.get("id")
    return {
        "id": str(event_id) if event_id is not None else None,
        "web_link": payload.get("webLink") or payload.get("web_link") or None,
        "online_meeting_url": (
            payload.get("onlineMeetingUrl")
            or payload.get("online_meeting_url")
            or online.get("joinUrl")
            or online.get("join_url")
            or None
        ),
        "subject": payload.get("subject"),
        "start": start,
        "end": end,
    }