Google Tag Manager setup

<script>
  window.dataLayer = window.dataLayer || [];
  window.OneSignalDeferred = window.OneSignalDeferred || [];

  OneSignalDeferred.push(function (OneSignal) {
    var rawExternalId = "{{ONESIGNAL_EXTERNAL_ID}}";

    // ---- Helpers ----
    function log() {
      console.log.apply(console, ["[OneSignal External ID]"].concat([].slice.call(arguments)));
    }

    function normalizeExternalId(v) {
      // GTM commonly substitutes these as strings
      if (
        v === undefined ||
        v === null ||
        v === "undefined" ||
        v === "null"
      ) return null;

      var s = String(v).trim();
      if (!s.length) return null;

      return s;
    }

    function pushDL(eventName, extra) {
      try {
        var payload = Object.assign({ event: eventName }, extra || {});
        window.dataLayer.push(payload);
      } catch (e) {
        // no-op
      }
    }

    function readStateSnapshot() {
      var snapshot = {
        onesignalId: null,
        externalId: null,
        pushSubscriptionId: null
      };

      try {
        snapshot.onesignalId = OneSignal.User && OneSignal.User.onesignalId;
        snapshot.externalId = OneSignal.User && OneSignal.User.externalId;
        snapshot.pushSubscriptionId =
          OneSignal.User &&
          OneSignal.User.PushSubscription &&
          OneSignal.User.PushSubscription.id;
      } catch (e) {
        log("Error reading OneSignal.User state", e);
      }

      return snapshot;
    }

    function isExternalIdApplied(targetExternalId) {
      var current = normalizeExternalId(OneSignal.User && OneSignal.User.externalId);
      return current === targetExternalId;
    }

    // ---- Initial logging ----
    log("Tag fired. rawExternalId:", rawExternalId, "type:", typeof rawExternalId);

    var externalId = normalizeExternalId(rawExternalId);
    log("Normalized externalId:", externalId, "type:", typeof externalId);

    if (!externalId) {
      log("Not calling login(): externalId missing/invalid");
      pushDL("OneSignalExternalIdMissing", { reason: "invalid_or_missing_external_id" });
      return;
    }

    // Optional: enable verbose OneSignal logs during testing
    if (OneSignal.Debug && OneSignal.Debug.setLogLevel) {
      OneSignal.Debug.setLogLevel("trace");
      log("Enabled OneSignal Debug log level: trace");
    }

    // ---- Attach User State observer ----
    var changeFired = false;

    OneSignal.User.addEventListener("change", function (event) {
      changeFired = true;

      log("User change event fired:", event);

      var snapshot = readStateSnapshot();
      log("User state snapshot:", snapshot);

      // Helpful: push snapshot-ish DL event (optional)
      pushDL("OneSignalUserStateChanged", {
        onesignal_id: snapshot.onesignalId || "",
        external_id: normalizeExternalId(snapshot.externalId) || "",
        push_subscription_id: snapshot.pushSubscriptionId || ""
      });
    });

    // ---- Login + confirm + retry ----
    var attempt = 0;
    var MAX_RETRIES = 3;
    var CONFIRM_WINDOW_MS = 1500;
    var BASE_BACKOFF_MS = 500;

    function doLogin() {
      attempt += 1;
      changeFired = false;

      log("Calling OneSignal.login()", { externalId: externalId, attempt: attempt });

      OneSignal.login(externalId)
        .then(function () {
          log("OneSignal.login() promise resolved");
          waitForConfirmation();
        })
        .catch(function (e) {
          log("OneSignal.login() promise rejected", e);
          retry("promise_rejected");
        });
    }

    function waitForConfirmation() {
      var start = Date.now();

      (function check() {
        if (isExternalIdApplied(externalId)) {
          log("Confirmed externalId applied via state check:", externalId);

          var snapshot = readStateSnapshot();
          log("Final state snapshot:", snapshot);

          pushDL("OneSignalExternalIdSet", {
            external_id: externalId,
            attempt: attempt,
            push_subscription_id: snapshot.pushSubscriptionId || ""
          });

          return;
        }

        if (changeFired) {
          log("Change event observed but externalId not yet reflected; waiting...");
        }

        if (Date.now() - start >= CONFIRM_WINDOW_MS) {
          log("No confirmation within window", {
            attempt: attempt,
            changeFired: changeFired,
            currentExternalId: normalizeExternalId(OneSignal.User && OneSignal.User.externalId)
          });

          retry("no_confirmation");
          return;
        }

        setTimeout(check, 100);
      })();
    }

    function retry(reason) {
      if (attempt >= MAX_RETRIES) {
        log("Giving up after max retries", { attempts: attempt, reason: reason });

        var snapshot = readStateSnapshot();
        log("State at give-up:", snapshot);

        pushDL("OneSignalExternalIdSetFailed", {
          external_id: externalId,
          reason: reason,
          attempts: attempt,
          push_subscription_id: snapshot.pushSubscriptionId || ""
        });

        return;
      }

      var delay = BASE_BACKOFF_MS * Math.pow(2, attempt - 1);
      log("Retrying login after delay", { delayMs: delay, reason: reason, nextAttempt: attempt + 1 });

      setTimeout(doLogin, delay);
    }

    // If already applied, don't spam login()
    if (isExternalIdApplied(externalId)) {
      log("ExternalId already applied; skipping login.", externalId);

      var snapshot = readStateSnapshot();
      log("Current state snapshot:", snapshot);

      pushDL("OneSignalExternalIdAlreadySet", {
        external_id: externalId,
        push_subscription_id: snapshot.pushSubscriptionId || ""
      });

      return;
    }

    // Kick it off
    doLogin();
  });
</script>