Source

// Page ranges people type for splitting, like "1-3, 5, 8-".

/**
 * Reads ranges against `total` pages. Returns 1-based inclusive pairs,
 * or a sentence saying what is wrong.
 */
export function parseRanges(text: string, total: number): [number, number][] | string {
  const parts = text.split(/[,;]+/).map((s) => s.trim()).filter(Boolean);
  if (!parts.length) return "Type the pages for each new PDF, like 1-3, 4-6.";
  const out: [number, number][] = [];
  for (const part of parts) {
    const m = part.match(/^(\d*)\s*[-–]\s*(\d*)$|^(\d+)$/);
    if (!m) return `"${part}" is not a page or a range. Use numbers like 2 or 4-7.`;
    const a = Number(m[3] ?? (m[1] || 1));
    const b = Number(m[3] ?? (m[2] || total));
    if (a < 1 || b < 1 || a > total || b > total) return `There ${total === 1 ? "is 1 page" : `are ${total} pages`}, so ${part} is out of range.`;
    if (a > b) return `${part} goes backwards. Write it as ${b}-${a}.`;
    out.push([a, b]);
  }
  return out;
}