// Website-Analyse: Skript-Tag in veröffentlichte HTML-Dateien einsetzen und Datenschutz-Zusatzseite schreiben.
import * as nodeFs from 'node:fs/promises';
import { join } from 'node:path';

export const RE_SITE_KEY = /^[a-z0-9]{16,40}$/;
export const RE_COLOR = /^#[0-9a-f]{6}$/;
const MAX_HTML_BYTES = 5 * 1024 * 1024;
const PAGE = 'datenschutz-analyse.html';
const TEMPLATE_URL = new URL('./templates/datenschutz-analyse.html', import.meta.url);

const esc = (s) => String(s).replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;').replace(/'/g, '&#39;');

// Interne Kommentare dürfen nie veröffentlicht werden.
export const stripComments = (t) => t.replace(/<!--[\s\S]*?-->\s*?\n?/g, '');

export const isValidBase = (b) => typeof b === 'string' && /^https:\/\/[^\s"'<>]+\/$/.test(b);

export function scriptTag(analytics, baseUrl) {
  // Attributwerte nur aus geprüften Eingaben (Regex), daher ohne Maskierung sicher.
  return `<script data-wk-analytics src="${baseUrl}w.js?s=${analytics.siteKey}" data-site="${analytics.siteKey}" data-color="${analytics.color}" defer></script>`;
}

// Spannen, in denen Marker nichts zu suchen haben: Kommentare, script, style, textarea, template (ohne Verschachtelungs-Logik).
function findSpans(s) {
  const spans = [];
  const re = /<!--|<(script|style|textarea|template)\b/gi;
  let m;
  while ((m = re.exec(s))) {
    let end;
    let kind = 'raw';
    if (m[0] === '<!--') {
      const e = s.indexOf('-->', m.index + 4);
      end = e < 0 ? s.length : e + 3;
      kind = 'comment';
    } else {
      const close = new RegExp(`</${m[1]}\\s*>`, 'ig');
      close.lastIndex = m.index + m[0].length;
      const c = close.exec(s);
      end = c ? c.index + c[0].length : s.length;
      if (m[1].toLowerCase() === 'script') kind = 'script';
    }
    spans.push({ start: m.index, end, kind });
    re.lastIndex = end;
  }
  return spans;
}

// Arbeitet auf latin1-Zeichenketten (1 Byte = 1 Zeichen), damit beliebige Kodierungen byte-genau erhalten bleiben.
export function injectIntoHtml(buf, tag) {
  let s = buf.toString('latin1');
  const spans = findSpans(s);
  const olds = spans.filter((x) => x.kind === 'script' && /\bdata-wk-analytics\b/i.test(s.slice(x.start, s.indexOf('>', x.start) + 1)));
  if (olds.length) {
    for (let i = olds.length - 1; i >= 0; i--) s = s.slice(0, olds[i].start) + (i === 0 ? tag : '') + s.slice(olds[i].end);
    return Buffer.from(s, 'latin1');
  }
  let masked = s;
  for (const x of spans) masked = masked.slice(0, x.start) + ' '.repeat(x.end - x.start) + masked.slice(x.end);
  const head = masked.search(/<\/head\s*>/i);
  if (head >= 0) s = s.slice(0, head) + tag + s.slice(head);
  else {
    const m = /<body\b[^>]*>/i.exec(masked);
    if (m) { const at = m.index + m[0].length; s = s.slice(0, at) + tag + s.slice(at); } else s = tag + s;
  }
  return Buffer.from(s, 'latin1');
}

async function* walk(fs, dir) {
  for (const e of await fs.readdir(dir, { withFileTypes: true })) {
    if (e.name.startsWith('.') || e.name === 'node_modules') continue;
    const p = join(dir, e.name);
    if (e.isDirectory()) yield* walk(fs, p);
    else if (e.isFile() && /\.html?$/i.test(e.name)) yield p;
  }
}

export async function injectAnalytics(dir, analytics, { baseUrl, onLine, fs = nodeFs } = {}) {
  if (!analytics) return;
  if (!RE_SITE_KEY.test(analytics.siteKey || '')) throw new Error('Analyse: ungültiger siteKey');
  if (!RE_COLOR.test(analytics.color || '')) throw new Error('Analyse: ungültige Farbe');
  if (!isValidBase(baseUrl)) throw new Error('Analyse: ungültige öffentliche Basis-URL');
  const tag = scriptTag(analytics, baseUrl);
  const p = analytics.privacy || {};
  const template = stripComments(await fs.readFile(TEMPLATE_URL, 'utf8'));
  const withAddr = p.address ? template.replace(/\{\{#address\}\}|\{\{\/address\}\}/g, '') : template.replace(/\{\{#address\}\}[\s\S]*?\{\{\/address\}\}/g, '');
  const page = withAddr.replace(/\{\{(company|address|email)\}\}/g, (_, k) => esc(p[k] ?? ''));
  await fs.writeFile(join(dir, PAGE), page, 'utf8');
  await fs.chmod(join(dir, PAGE), 0o644);
  let n = 0;
  for await (const file of walk(fs, dir)) {
    const rel = file.slice(dir.length + 1);
    if ((await fs.stat(file)).size > MAX_HTML_BYTES) { onLine?.(`Analyse: ${rel} übersprungen (größer als 5 MB)`); continue; }
    await fs.writeFile(file, injectIntoHtml(await fs.readFile(file), tag));
    n++;
  }
  onLine?.(`Analyse-Skript in ${n} HTML-Datei(en) eingesetzt`);
}