/**
 * Default per-account send rate, mirroring `BOT_MAX_SEND_PER_MINUTE`
 * in the bot env. The web bundle hardcodes this — operators who tune
 * the bot env are expected to redeploy web with the matching value.
 */
export const ASSUMED_RATE_PER_MINUTE = 40;

const ETA_BUFFER = 1.15;

/**
 * Pure ETA helper. Given a target count and a fire time, returns the
 * estimated duration in whole minutes and the projected finish
 * timestamp.
 *
 * Calculation:
 *   ceil((targetCount / ratePerMinute) * 1.15)   minutes
 *   estimatedFinishAt = fireAt + that many minutes
 *
 * Floor of 1 minute when targetCount > 0 (anything non-zero takes at
 * least a minute to feel real). Returns 0 minutes when targetCount
 * is zero — the run is a no-op.
 */
export function estimateRunDuration(opts: {
  targetCount: number;
  ratePerMinute?: number;
  fireAt: Date;
}): { durationMinutes: number; estimatedFinishAt: Date } {
  const rate = opts.ratePerMinute ?? ASSUMED_RATE_PER_MINUTE;
  if (rate <= 0) throw new Error("ratePerMinute must be > 0");
  if (opts.targetCount <= 0) {
    return { durationMinutes: 0, estimatedFinishAt: new Date(opts.fireAt) };
  }
  const raw = (opts.targetCount / rate) * ETA_BUFFER;
  const durationMinutes = Math.max(1, Math.ceil(raw));
  const estimatedFinishAt = new Date(
    opts.fireAt.getTime() + durationMinutes * 60_000,
  );
  return { durationMinutes, estimatedFinishAt };
}