export function relativeTime(iso: string | null): string {
  if (!iso) return "";
  const then = new Date(iso).getTime();
  const secs = Math.max(0, (Date.now() - then) / 1000);
  const units: [number, string][] = [
    [60, "s"],
    [3600, "min"],
    [86400, "h"],
    [604800, "d"],
    [2592000, "wk"],
    [31536000, "mo"],
  ];
  if (secs < 60) return "just now";
  for (let i = 0; i < units.length - 1; i++) {
    const [, label] = units[i];
    const next = units[i + 1][0];
    if (secs < next) {
      const v = Math.floor(secs / units[i][0]);
      return `${v} ${label} ago`;
    }
  }
  const years = Math.floor(secs / 31536000);
  if (years >= 1) return `${years} yr ago`;
  const months = Math.floor(secs / 2592000);
  return `${months} mo ago`;
}

export function formatDuration(sec: number | null): string {
  if (sec == null) return "";
  const h = Math.floor(sec / 3600);
  const m = Math.floor((sec % 3600) / 60);
  const s = Math.floor(sec % 60);
  const pad = (n: number) => String(n).padStart(2, "0");
  return h > 0 ? `${h}:${pad(m)}:${pad(s)}` : `${m}:${pad(s)}`;
}

/** Coarse, human ETA for a remaining duration in seconds ("~3 hours", "~2 days"). */
export function formatEta(seconds: number): string {
  if (seconds <= 0) return "done";
  const hours = seconds / 3600;
  if (hours < 1) return "< 1 hour";
  if (hours < 24) {
    const h = Math.round(hours);
    return `~${h} hour${h === 1 ? "" : "s"}`;
  }
  const d = Math.round(hours / 24);
  return `~${d} day${d === 1 ? "" : "s"}`;
}

export function formatViews(n: number | null): string {
  if (n == null) return "";
  if (n >= 1e9) return `${(n / 1e9).toFixed(1).replace(/\.0$/, "")}B`;
  if (n >= 1e6) return `${(n / 1e6).toFixed(1).replace(/\.0$/, "")}M`;
  if (n >= 1e3) return `${(n / 1e3).toFixed(1).replace(/\.0$/, "")}K`;
  return String(n);
}