"""Internal demonstration: deterministic ordering of replayed events."""
from datetime import datetime, timezone

def normalize_events(events):
    seen = {}
    for event in events:
        if not isinstance(event, dict):
            raise ValueError('Each event must be an object')
        key, at, kind = (event.get(k) for k in ('id','at','type'))
        if not all(isinstance(v,str) and v.strip() for v in (key,at,kind)):
            raise ValueError('id, at and type must be non-empty strings')
        try:
            stamp = datetime.fromisoformat(at.replace('Z','+00:00'))
            if stamp.tzinfo is None or stamp.utcoffset() is None:
                raise ValueError('A timezone offset is required')
            stamp = stamp.astimezone(timezone.utc)
        except (ValueError, OverflowError) as error:
            raise ValueError('Invalid timestamp') from error
        value = (stamp, kind)
        if key in seen and seen[key] != value:
            raise ValueError('Conflicting duplicate id: ' + key)
        seen[key] = value
    return [{'id': key, 'at': stamp.isoformat(timespec='microseconds').replace('+00:00','Z'), 'type': kind}
            for key, (stamp, kind) in sorted(seen.items(), key=lambda pair:(pair[1][0],pair[0]))]