analytics.js

function getGoogleAnalyticsId() {
  const id = String(process.env.GOOGLE_ANALYTICS_ID || "").trim();
  return /^G-[A-Z0-9]+$/i.test(id) ? id : "";
}

function getGoogleAnalyticsTag() {
  const id = getGoogleAnalyticsId();
  if (!id) return "";

  return `
  <!-- Google Analytics -->
  <script async src="https://www.googletagmanager.com/gtag/js?id=${encodeURIComponent(id)}"></script>
  <script>
    window.dataLayer = window.dataLayer || [];
    function gtag(){dataLayer.push(arguments);}
    gtag("js", new Date());
    gtag("config", ${JSON.stringify(id)});
  </script>`;
}

function injectGoogleAnalytics(html) {
  const tag = getGoogleAnalyticsTag();
  if (!tag || typeof html !== "string" || !html.includes("</head>")) {
    return html;
  }

  return html.replace("</head>", `${tag}\n</head>`);
}

module.exports = { injectGoogleAnalytics };