yanting/lib/app.dart

import 'package:flutter/material.dart';

import 'data/api/report_data_source.dart';
import 'features/shell_page.dart';
import 'theme/app_theme.dart';

class MyApp extends StatelessWidget {
  const MyApp({required this.dataSource, super.key});

  final ReportDataSource dataSource;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: '研听',
      debugShowCheckedModeBanner: false,
      theme: buildAppTheme(),
      scrollBehavior: const WhitespaceStretchScrollBehavior(),
      home: ShellPage(dataSource: dataSource),
    );
  }
}

class WhitespaceStretchScrollBehavior extends MaterialScrollBehavior {
  const WhitespaceStretchScrollBehavior();

  @override
  Widget buildOverscrollIndicator(
    BuildContext context,
    Widget child,
    ScrollableDetails details,
  ) {
    return _WhitespaceStretchIndicator(child: child);
  }
}

class _WhitespaceStretchIndicator extends StatefulWidget {
  const _WhitespaceStretchIndicator({required this.child});

  final Widget child;

  @override
  State<_WhitespaceStretchIndicator> createState() =>
      _WhitespaceStretchIndicatorState();
}

class _WhitespaceStretchIndicatorState
    extends State<_WhitespaceStretchIndicator>
    with SingleTickerProviderStateMixin {
  static const double _maxStretch = 64;
  static const double _dragResistance = 0.38;

  late final AnimationController _offsetController =
      AnimationController.unbounded(vsync: this)..addListener(_onTick);

  @override
  Widget build(BuildContext context) {
    return NotificationListener<ScrollNotification>(
      onNotification: _handleScrollNotification,
      child: ClipRect(
        child: Transform.translate(
          offset: Offset(0, _offsetController.value),
          child: widget.child,
        ),
      ),
    );
  }

  @override
  void dispose() {
    _offsetController.dispose();
    super.dispose();
  }

  bool _handleScrollNotification(ScrollNotification notification) {
    if (notification.metrics.axis != Axis.vertical) {
      return false;
    }
    if (notification is OverscrollNotification) {
      final overscroll = notification.overscroll;
      final atTop =
          notification.metrics.pixels <= notification.metrics.minScrollExtent;
      final atBottom =
          notification.metrics.pixels >= notification.metrics.maxScrollExtent;
      if (atTop && overscroll < 0) {
        _setOffset(
          (_offsetController.value - overscroll * _dragResistance).clamp(
            0,
            _maxStretch,
          ),
        );
      } else if (atBottom && overscroll > 0) {
        _setOffset(
          (_offsetController.value - overscroll * _dragResistance).clamp(
            -_maxStretch,
            0,
          ),
        );
      }
    }
    if (notification is ScrollUpdateNotification &&
        notification.dragDetails == null) {
      _releaseOffset();
    }
    if (notification is ScrollEndNotification) {
      _releaseOffset();
    }
    return false;
  }

  void _setOffset(num next) {
    if (next == _offsetController.value) {
      return;
    }
    _offsetController.stop();
    _offsetController.value = next.toDouble();
  }

  void _releaseOffset() {
    if (_offsetController.value == 0) {
      return;
    }
    _offsetController.animateTo(
      0,
      duration: const Duration(milliseconds: 260),
      curve: Curves.easeOutCubic,
    );
  }

  void _onTick() {
    if (mounted) {
      setState(() {});
    }
  }
}