// Small, forgiving HTML helpers. Not a parser: enough for <meta>, <link>, <div style>, <img src>.

const NAMED: Readonly<Record<string, string>> = { amp: "&", lt: "<", gt: ">", quot: '"', apos: "'" };

export function decodeEntities(s: string): string {
  return s.replace(/&(#x[0-9a-f]+|#\d+|[a-z]+);/gi, (match, entity: string) => {
    const e = entity.toLowerCase();
    if (e.startsWith("#")) {
      const code = e.startsWith("#x") ? parseInt(e.slice(2), 16) : parseInt(e.slice(1), 10);
      // Malformed pages carry entities like &#99999999;: leave them as written rather than throw.
      return Number.isInteger(code) && code >= 0 && code <= 0x10ffff ? String.fromCodePoint(code) : match;
    }
    return NAMED[e] ?? match;
  });
}

export function parseAttributes(tag: string): Record<string, string> {
  const out: Record<string, string> = {};
  const body = tag.replace(/^<\s*[\w-]+/, "").replace(/\/?\s*>$/, "");
  for (const m of body.matchAll(/([^\s=/"'>]+)(?:\s*=\s*(?:"([^"]*)"|'([^']*)'|([^\s"'>]+)))?/g)) {
    const name = m[1]!.toLowerCase();
    if (!(name in out)) out[name] = decodeEntities(m[2] ?? m[3] ?? m[4] ?? "");
  }
  return out;
}

export function findTags(html: string, name: string): Record<string, string>[] {
  return [...html.matchAll(new RegExp(`<${name}\\b[^>]*>`, "gi"))].map((m) => parseAttributes(m[0]));
}

/** `<meta property|name="key" content="…">` */
export function metaContent(html: string, key: string): string | undefined {
  for (const a of findTags(html, "meta")) {
    if ((a.property ?? a.name) === key && a.content) return a.content;
  }
  return undefined;
}

export function textOf(fragment: string): string {
  return decodeEntities(fragment.replace(/<[^>]*>/g, " ")).replace(/\s+/g, " ").trim();
}