/**
 * Whether a request announces itself as software rather than a person.
 *
 * The voice measurement divides durable use by impressions, and crawlers are
 * impressions that can never convert — every one that slips in drags each
 * weight toward zero. The dwell-or-scroll beat already filters most of them,
 * but Google's renderer runs timers, so a declared bot can pass a four-second
 * dwell without a person existing.
 *
 * Declared is the operative word. This reads the User-Agent string, which
 * catches every honest crawler — search engines, link unfurlers, validators —
 * and none of the dishonest ones. That is the right trade here: a liar gets
 * counted as a visitor who never signed up, which is noise the model already
 * survives; there is nothing worth defending beyond that, since the only
 * thing at stake is the quality of our own statistics.
 */
const BOT_UA =
  /bot|crawler|spider|crawling|slurp|bingpreview|headless|lighthouse|facebookexternalhit|whatsapp|telegram|skypeuripreview|discordbot|embedly|pinterest|linkedinbot|vkshare|validator|fetcher|monitor|scrape/i;

export function isDeclaredBot(userAgent: string | undefined): boolean {
  return userAgent !== undefined && BOT_UA.test(userAgent);
}