/**
 * Defines what a slug is: the readable name of a category, a dump or a
 * playlist in a page URL. The server makes and checks slugs with it, and the
 * edit forms prefill their slug field with {@link slugify}.
 *
 * @module
 */

/** The longest a dump's or a playlist's slug may be. */
export const SLUG_MAX = 60;

/**
 * Matches a well-formed slug: lowercase letters and digits, in words joined by
 * single hyphens. Categories, dumps and playlists share it.
 */
export const SLUG_RE: RegExp = /^[a-z0-9]+(?:-[a-z0-9]+)*$/;

/**
 * Checks whether `slug` matches {@link SLUG_RE} and is at most `max`
 * characters long.
 */
export function isValidSlug(slug: string, max: number = SLUG_MAX): boolean {
  return slug.length <= max && SLUG_RE.test(slug);
}

/**
 * Turns `title` into lowercase ASCII words joined by hyphens, at most `max`
 * characters long, cut at a hyphen when it must be cut. Accents are dropped,
 * and a title with no ASCII letter or digit gives `untitled`. The result
 * always passes {@link isValidSlug}.
 */
export function slugify(title: string, max: number = SLUG_MAX): string {
  const slug = title
    .toLowerCase()
    .normalize("NFD")
    // NFD splits an accented letter into the letter and a combining mark.
    .replace(/[\u0300-\u036f]/g, "")
    .replace(/[^a-z0-9]+/g, "-")
    .substring(0, max + 1)
    .replace(/^-+/, "");
  // Cut at the last hyphen within `max` rather than in the middle of a word,
  // unless the first word alone is longer.
  const cut = slug.length > max
    ? slug.substring(
      0,
      slug.lastIndexOf("-", max) > 0 ? slug.lastIndexOf("-", max) : max,
    )
    : slug;
  return cut.replace(/-+$/, "") || "untitled";
}