export function formatDuration(ms: number): string {
  const totalSec = Math.floor(ms / 1000);
  const h = Math.floor(totalSec / 3600);
  const m = Math.floor((totalSec % 3600) / 60);
  const s = totalSec % 60;
  if (h > 0)
    return `${h}:${String(m).padStart(2, '0')}:${String(s).padStart(2, '0')}`;
  return `${m}:${String(s).padStart(2, '0')}`;
}

export function formatFileSize(bytes: number): string {
  if (bytes < 1024) return `${bytes} B`;
  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
  if (bytes < 1024 * 1024 * 1024)
    return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
  return `${(bytes / (1024 * 1024 * 1024)).toFixed(2)} GB`;
}

export function formatDateTime(iso: string | undefined): string | undefined {
  if (!iso) return undefined;
  const d = new Date(iso);
  if (Number.isNaN(d.getTime())) return undefined;
  return new Intl.DateTimeFormat(undefined, {
    dateStyle: 'medium',
    timeStyle: 'short',
  }).format(d);
}

/** Human "X days Y hours" style for big spans (e.g. total library playtime).
 * Shows the two most-significant non-zero units; falls back to "0m". */
export function formatLongDuration(seconds: number): string {
  if (seconds <= 0) return '0m';
  const days = Math.floor(seconds / 86400);
  const hours = Math.floor((seconds % 86400) / 3600);
  const mins = Math.floor((seconds % 3600) / 60);
  const parts: string[] = [];
  if (days) parts.push(`${days}d`);
  if (hours) parts.push(`${hours}h`);
  if (mins && parts.length < 2) parts.push(`${mins}m`);
  return parts.slice(0, 2).join(' ') || '0m';
}

export function formatCount(n: number): string {
  if (n < 1000) return String(n);
  if (n < 1_000_000) return `${(n / 1000).toFixed(1)}K`;
  return `${(n / 1_000_000).toFixed(1)}M`;
}