/** "1.4 MB" in the UI's language. */
export function formatBytes(bytes: number, locale: string): string {
  const units = ["byte", "kilobyte", "megabyte", "gigabyte"] as const;
  let value = bytes;
  let unit = 0;
  while (value >= 1024 && unit < units.length - 1) {
    value /= 1024;
    unit++;
  }
  return new Intl.NumberFormat(locale, {
    style: "unit",
    unit: units[unit],
    unitDisplay: "short",
    maximumFractionDigits: unit === 0 ? 0 : 1,
  }).format(value);
}

/** "3 days ago" / "منذ 3 أيام", or null for never. */
export function timeAgo(iso: string | null, locale: string): string | null {
  if (!iso) return null;
  const seconds = (new Date(iso).getTime() - Date.now()) / 1000;
  const rtf = new Intl.RelativeTimeFormat(locale, { numeric: "auto" });
  const steps: [Intl.RelativeTimeFormatUnit, number][] = [
    ["year", 31536000],
    ["month", 2592000],
    ["week", 604800],
    ["day", 86400],
    ["hour", 3600],
    ["minute", 60],
  ];
  for (const [unit, size] of steps) {
    if (Math.abs(seconds) >= size) return rtf.format(Math.round(seconds / size), unit);
  }
  return rtf.format(0, "minute");
}

/** "Apr 2026" from "2026-04". */
export function monthLabel(month: string, locale: string): string {
  const [year, m] = month.split("-").map(Number);
  return new Intl.DateTimeFormat(locale, { month: "short", year: "numeric" }).format(
    new Date(year, m - 1, 1)
  );
}

export function formatDateTime(iso: string, locale: string): string {
  return new Intl.DateTimeFormat(locale, { dateStyle: "medium", timeStyle: "short" }).format(
    new Date(iso)
  );
}