const MAX_SLUG_LENGTH = 96;

/**
 * Turns arbitrary text into a URL-safe slug: lowercase ASCII words joined
 * by single hyphens. Returns "" when nothing usable remains, so callers
 * can decide on a fallback.
 */
export function slugify(input: string): string {
  return input
    .normalize("NFKD")
    .replace(/[̀-ͯ]/g, "") // strip combining diacritics
    .toLowerCase()
    .replace(/[^a-z0-9]+/g, "-")
    .replace(/^-+|-+$/g, "")
    .slice(0, MAX_SLUG_LENGTH)
    .replace(/-+$/g, "");
}

/**
 * Finds a free slug by appending -2, -3, ... to the base while `isTaken`
 * reports a conflict. The base falls back to "untitled" when empty.
 */
export async function ensureUniqueSlug(
  base: string,
  isTaken: (slug: string) => Promise<boolean>,
): Promise<string> {
  const root = base || "untitled";
  let candidate = root;
  for (let suffix = 2; await isTaken(candidate); suffix++) {
    if (suffix > 500) {
      throw new Error(`Could not find a free slug for "${root}"`);
    }
    candidate = `${root}-${suffix}`;
  }
  return candidate;
}