Add segment observer

lib/segment_observer.dart

@@ -0,0 +1,47 @@
+import 'package:flutter/widgets.dart';
+import 'package:flutter_segment_plus/flutter_segment_plus.dart';
+
+typedef ScreenNameExtractor = String? Function(RouteSettings settings);
+
+String? defaultNameExtractor(RouteSettings settings) => settings.name;
+
+class SegmentObserver extends RouteObserver<PageRoute<dynamic>> {
+  SegmentObserver({
+    required this.segment,
+    this.nameExtractor = defaultNameExtractor,
+  });
+
+  final ScreenNameExtractor nameExtractor;
+  final FlutterSegmentPlus segment;
+
+  void _sendScreenView(PageRoute<dynamic> route) {
+    final String? screenName = nameExtractor(route.settings);
+    if (screenName != null) {
+      segment.screen(screenName: screenName);
+    }
+  }
+
+  @override
+  void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
+    super.didPush(route, previousRoute);
+    if (route is PageRoute) {
+      _sendScreenView(route);
+    }
+  }
+
+  @override
+  void didReplace({Route<dynamic>? newRoute, Route<dynamic>? oldRoute}) {
+    super.didReplace(newRoute: newRoute, oldRoute: oldRoute);
+    if (newRoute is PageRoute) {
+      _sendScreenView(newRoute);
+    }
+  }
+
+  @override
+  void didPop(Route<dynamic> route, Route<dynamic>? previousRoute) {
+    super.didPop(route, previousRoute);
+    if (previousRoute is PageRoute && route is PageRoute) {
+      _sendScreenView(previousRoute);
+    }
+  }
+}