// Shared helpers for scrapers.

export const USER_AGENT =
  "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0 Safari/537.36";

// Upper half (0xA0-0xFF) of ISO-8859-2, which Bun's TextDecoder does not support.
const LATIN2_HIGH =
  " Ą˘Ł¤ĽŚ§¨ŠŞŤŹ­ŽŻ°ą˛ł´ľśˇ¸šşťź˝žżŔÁÂĂÄĹĆÇČÉĘËĚÍÎĎĐŃŇÓÔŐÖ×ŘŮÚŰÜÝŢßŕáâăäĺćçčéęëěíîďđńňóôőö÷řůúűüýţ˙";

function decodeLatin2(bytes: Uint8Array): string {
  let out = "";
  for (const b of bytes) out += b < 0xa0 ? String.fromCharCode(b) : LATIN2_HIGH[b - 0xa0];
  return out;
}

/** Fetch a page and decode it according to its declared charset. */
export async function fetchHtml(url: string): Promise<string> {
  const res = await fetch(url, { headers: { "User-Agent": USER_AGENT } });
  if (!res.ok) throw new Error(`GET ${url} -> HTTP ${res.status}`);
  const bytes = new Uint8Array(await res.arrayBuffer());
  const charset = /charset=([\w-]+)/i.exec(res.headers.get("content-type") ?? "")?.[1]?.toLowerCase() ?? "utf-8";
  if (charset === "iso-8859-2" || charset === "latin2") return decodeLatin2(bytes);
  try {
    return new TextDecoder(charset).decode(bytes);
  } catch {
    return new TextDecoder("utf-8").decode(bytes);
  }
}

const NAMED_ENTITIES: Record<string, string> = {
  amp: "&", lt: "<", gt: ">", quot: '"', apos: "'", nbsp: " ", raquo: "»", laquo: "«",
  scaron: "š", Scaron: "Š", zcaron: "ž", Zcaron: "Ž", ccaron: "č", Ccaron: "Č",
  ndash: "–", mdash: "—", lsquo: "‘", rsquo: "’", ldquo: "“", rdquo: "”", bdquo: "„", hellip: "…",
};

/** Decode HTML entities (HTMLRewriter text chunks are not decoded). */
export function decodeEntities(s: string): string {
  return s.replace(/&(#x[0-9a-f]+|#\d+|\w+);/gi, (m, e: string) => {
    if (e[0] === "#") {
      const code = e[1] === "x" || e[1] === "X" ? parseInt(e.slice(2), 16) : parseInt(e.slice(1), 10);
      return Number.isFinite(code) ? String.fromCodePoint(code) : m;
    }
    return NAMED_ENTITIES[e] ?? NAMED_ENTITIES[e.toLowerCase()] ?? m;
  });
}

export const clean = (s: string) => decodeEntities(s).replace(/\s+/g, " ").trim();

/** ASCII URL/ID slug: "Inženir (m/ž)" -> "inzenir-m-z". */
export const slugify = (s: string) =>
  s
    .normalize("NFD")
    .replace(/[̀-ͯ]/g, "")
    .replace(/[^A-Za-z0-9]+/g, "-")
    .replace(/^-|-$/g, "")
    .toLowerCase();