/// Skips building while another route covers this one, then rebuilds on pop.
library;

import 'package:flutter/material.dart';

/// Shared observer — register on [MaterialApp.navigatorObservers].
final RouteObserver<ModalRoute<void>> appRouteObserver =
    RouteObserver<ModalRoute<void>>();

/// Builds via [builder] only when this route is not covered by a pushed page.
class SkipBuildWhenCovered extends StatefulWidget {
  const SkipBuildWhenCovered({
    super.key,
    required this.builder,
    this.placeholder = const SizedBox.expand(),
  });

  final WidgetBuilder builder;
  final Widget placeholder;

  @override
  State<SkipBuildWhenCovered> createState() => _SkipBuildWhenCoveredState();
}

class _SkipBuildWhenCoveredState extends State<SkipBuildWhenCovered>
    with RouteAware {
  var _covered = false;

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    final route = ModalRoute.of(context);
    if (route is PageRoute) {
      appRouteObserver.subscribe(this, route);
    }
  }

  @override
  void dispose() {
    appRouteObserver.unsubscribe(this);
    super.dispose();
  }

  @override
  void didPushNext() {
    if (!_covered) setState(() => _covered = true);
  }

  @override
  void didPopNext() {
    if (_covered) setState(() => _covered = false);
  }

  @override
  Widget build(BuildContext context) {
    if (_covered) return widget.placeholder;
    return widget.builder(context);
  }
}