const SI_THRESHOLDS = [
  { limit: 1_000_000_000, divisor: 1_000_000_000, suffix: 'G' },
  { limit: 1_000_000, divisor: 1_000_000, suffix: 'M' },
  { limit: 1_000, divisor: 1_000, suffix: 'K' },
] as const;

export function formatSI(v: number, locale?: string, fractionDigits?: number): string {
  const abs = Math.abs(v);
  const fd = fractionDigits ?? 3;
  for (const { limit, divisor, suffix } of SI_THRESHOLDS) {
    if (abs >= limit) {
      const formatted = new Intl.NumberFormat(locale, {
        maximumFractionDigits: fd,
        minimumFractionDigits: 0,
      }).format(v / divisor);
      return `${formatted}${suffix}`;
    }
  }
  return new Intl.NumberFormat(locale, {
    maximumFractionDigits: fractionDigits != null ? fractionDigits : 0,
    minimumFractionDigits: 0,
  }).format(v);
}