Install on Flutter

// lib/analytics/veritametrics_observer.dart
import 'dart:async';
import 'dart:html' as html;
import 'dart:js' as js;
import 'package:flutter/widgets.dart';

/// VeritaMetrics Analytics Observer for Flutter Web.
///
/// How to use:
/// 1. Add this file to your project.
/// 2. In your main MaterialApp (or CupertinoApp), add an instance of this
///    class to the navigatorObservers list.
///
/// MaterialApp(
///   navigatorObservers: [
///     VeritaMetricsObserver(
///       siteId: 'YOUR-SITE-ID',
///       trackingDomain: 'www.veritametrics.com',
///     ),
///   ],
///   // ... other properties
/// );
///
class VeritaMetricsObserver extends RouteObserver<PageRoute<dynamic>> {
  final String siteId;
  final String trackingDomain;

  VeritaMetricsObserver({
    required this.siteId,
    required this.trackingDomain,
  });

  void _trackPageView() {
    // We delay tracking slightly to ensure the document title has been updated by Flutter.
    Timer(const Duration(milliseconds: 100), () {
      if (siteId.isEmpty || trackingDomain.isEmpty) return;

      // 1. Initialize the Async Command Queue (if it doesn't exist)
      // This JS shim makes window.verita() available immediately.
      final shimScript = html.ScriptElement()
      ..text = 'window.verita=window.verita||function(){(window.verita.q=window.verita.q||[]).push(arguments)};window.verita.l=new Date().getTime();';
      html.document.head?.append(shimScript);

      // 2. Load the enhanced tracker script.
      // We check if it's already been loaded to avoid duplicates on navigation.
      final scriptId = 'veritametrics-tracker';
      if (html.document.getElementById(scriptId) == null) {
        final script = html.ScriptElement()
        ..id = scriptId
        ..src = 'https://${trackingDomain}/api/tracker.js?siteId=$siteId'
        ..async = true
        ..defer = true;
        script.dataset['siteId'] = siteId;
        script.dataset['trackingDomain'] = trackingDomain;
        html.document.head?.append(script);
      }

      // 3. Send the pageview command using the queue.
      // js.context.callMethod reaches window.verita directly. dart:html's Window
      // has no eval(), so calling one does not compile.
      js.context.callMethod('verita', ['trackPageView']);
    });
  }

  @override
  void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
    super.didPush(route, previousRoute);
    // This fires for the initial route and all subsequent pushes.
    _trackPageView();
  }

  @override
  void didReplace({Route<dynamic>? newRoute, Route<dynamic>? oldRoute}) {
    super.didReplace(newRoute: newRoute, oldRoute: oldRoute);
    if (newRoute!= null) {
      _trackPageView();
    }
  }

  @override
  void didPop(Route<dynamic> route, Route<dynamic>? previousRoute) {
    super.didPop(route, previousRoute);
    if (previousRoute!= null) {
      _trackPageView();
    }
  }
}

/*
  A note on <noscript> support:
  Similar to React, a <noscript> tag cannot be managed from Dart code.
  The fallback pixel should be placed in the static web/index.html file
  of your Flutter project.

  <noscript>
    <img
      src="https://www.veritametrics.com/api/track-pageview?siteId=YOUR-SITE-ID"
      referrerpolicy="unsafe-url"
      alt=""
      width="1"
      height="1"
      style="display:none"
      aria-hidden="true"
    />
  </noscript>
*/