import 'package:flutter/material.dart';

import 'app_progress_indicator.dart';

/// Delays building [builder] until the enclosing route's enter animation has
/// finished. Some widgets (notably `SfPdfViewer`) call `localToGlobal` during
/// their first layout and assert with `RenderBox was not laid out` when an
/// ancestor page-transition `RenderTransform` still has no size mid-push.
/// Gating the mount behind the settled animation avoids that race.
class RouteTransitionGate extends StatefulWidget {
  const RouteTransitionGate({super.key, required this.builder, this.placeholder});

  final WidgetBuilder builder;

  /// Shown while the route is still animating in. Defaults to a centered
  /// large progress indicator.
  final Widget? placeholder;

  @override
  State<RouteTransitionGate> createState() => _RouteTransitionGateState();
}

class _RouteTransitionGateState extends State<RouteTransitionGate> {
  bool _ready = false;
  Animation<double>? _routeAnimation;

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    if (_ready || _routeAnimation != null) return;
    final animation = ModalRoute.of(context)?.animation;
    if (animation == null || animation.isCompleted) {
      _ready = true;
      return;
    }
    _routeAnimation = animation..addStatusListener(_onAnimationStatus);
  }

  void _onAnimationStatus(AnimationStatus status) {
    if (status == AnimationStatus.completed && mounted) {
      setState(() => _ready = true);
    }
  }

  @override
  void dispose() {
    _routeAnimation?.removeStatusListener(_onAnimationStatus);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    if (!_ready) {
      return widget.placeholder ??
          const Center(child: AppProgressIndicator.large());
    }
    return widget.builder(context);
  }
}