def classify_price(robux: int) -> str:
    if robux <= 99:
        return "low"
    elif robux <= 499:
        return "medium"
    else:
        return "high"

def enrich_event(event, game: str):
    """Adds game tag and derived fields."""
    event.data = event.data or {}
    # Inject game name into event data as a tag
    event.data["game"] = game
    # Derive price group for robux purchases
    if event.type == "robux_purchase" and "robux" in event.data:
        event.data["priceGroup"] = classify_price(event.data["robux"])
    return event