import { useEffect, useState } from 'react';
import { useLocation } from 'react-router-dom';
import { fetchConfig } from './api';
import { useCustomerAuth } from './customer/CustomerAuthContext';
import { brevoPage, startBrevoTracking, stopBrevoTracking } from './brevo';

/**
 * Drives the Brevo tracker from the two things that decide whether it may run
 * at all: the environment's key and the signed-in customer's consent (#56).
 *
 * Renders nothing. It exists as a component rather than a hook because it needs
 * both the router and the auth context, and mounting it inside `AppRoutes` is
 * what guarantees it sits under both — a hook called from the wrong place would
 * fail at runtime instead of being impossible to misplace.
 *
 * ## Why the gate is a server-computed field
 *
 * `analytics_consent` is not `marketing_consent`. The consent sentence was
 * widened to mention analytics, and the server reports this flag by comparing
 * the wording each customer actually agreed to against the current text. A
 * customer who consented to the older, email-only wording is not tracked. Never
 * substitute `marketing_consent` here — that is the exact retroactive widening
 * the field exists to prevent.
 *
 * A signed-out visitor has no consent record, so no key is ever used and the
 * script is never injected. Anonymous browsing is not reported at all.
 */
export default function BrevoTracking() {
  const { customer } = useCustomerAuth();
  const location = useLocation();
  const [trackerKey, setTrackerKey] = useState<string | null>(null);

  useEffect(() => {
    let cancelled = false;
    // Swallowed for the same reason main.tsx swallows its warm-up call: a
    // config that cannot be fetched is a broken deployment every other request
    // will report, and losing analytics is not worth surfacing to a customer.
    void fetchConfig()
      .then(config => { if (!cancelled) setTrackerKey(config.brevoTrackerKey); })
      .catch(() => {});
    return () => { cancelled = true; };
  }, []);

  const consented = customer?.analytics_consent === true;
  const email = customer?.email;

  // Start and stop are driven by the same effect so there is no state in which
  // consent has gone away and nothing has acted on it. Withdrawing consent,
  // signing out, and deleting the account all arrive here as `consented`
  // turning false, because each one ends with the customer no longer being a
  // consenting signed-in customer.
  useEffect(() => {
    if (consented && trackerKey && email) {
      startBrevoTracking(trackerKey, email);
    } else {
      stopBrevoTracking();
    }
  }, [consented, trackerKey, email]);

  // Declared after the effect above so that on the render where consent or the
  // key first arrives, tracking is started before this reports the route.
  //
  // The storefront is a single-page app: without this, the tracker's own
  // initial call would be the only page view it ever saw, and every customer
  // would look like they viewed one page and left.
  useEffect(() => {
    brevoPage(location.pathname);
  }, [location.pathname, consented, trackerKey]);

  return null;
}