// The page counter's browser end. One beacon per page view, one per click on an
// element that carries a `data-key` — that attribute is already on nearly every
// control, so it doubles as the feature's name. Nothing here may break the app:
// every path is wrapped, a refused beacon is simply not counted, and a visitor
// who asked not to be tracked is left alone.
const ENDPOINT = '/api/events';

type Kind = 'view' | 'click';

function send(kind: Kind, path: string, target?: string): void {
  try {
    if (navigator.doNotTrack === '1') return;
    const body = JSON.stringify({ kind, path, target });
    const blob = new Blob([body], { type: 'application/json' });
    // sendBeacon survives the page unload a click often triggers; the fetch is
    // the fallback for a browser that has no beacon (or refuses this one).
    if (navigator.sendBeacon?.(ENDPOINT, blob)) return;
    void fetch(ENDPOINT, {
      method: 'POST',
      body,
      keepalive: true,
      headers: { 'content-type': 'application/json' },
    }).catch(() => {});
  } catch {
    // Analytics is best-effort — a failure here must never reach the app.
  }
}

export function track(kind: Kind, path: string, target?: string): void {
  send(kind, path, target);
}

// Call once, before the first render. The view is recorded now; the click is
// recorded from one capturing listener on the document, so a control keeps its
// own handler and needs no tracking code of its own.
export function installTracking(): void {
  send('view', window.location.pathname);
  document.addEventListener(
    'click',
    (event) => {
      const node = event.target;
      const el = node instanceof Element ? node.closest('[data-key]') : null;
      const target = el?.getAttribute('data-key');
      if (target) send('click', window.location.pathname, target);
    },
    true,
  );
}