import 'package:flutter/material.dart';

class ExpandablePageView extends StatefulWidget {
  const ExpandablePageView({
    super.key,
    required this.itemCount,
    required this.itemBuilder,
    this.onPageChanged,
  });

  final int itemCount;
  final IndexedWidgetBuilder itemBuilder;
  final ValueChanged<int>? onPageChanged;

  @override
  State<ExpandablePageView> createState() => _ExpandablePageViewState();
}

class _ExpandablePageViewState extends State<ExpandablePageView> {
  late List<double> _heights;
  int _currentPage = 0;

  double get _currentHeight {
    if (_heights.isEmpty) {
      return 0;
    }
    final page = _currentPage.clamp(0, _heights.length - 1);
    return _heights[page];
  }

  @override
  void initState() {
    super.initState();
    _heights = List<double>.filled(widget.itemCount, 0, growable: true);
  }

  @override
  void didUpdateWidget(covariant ExpandablePageView oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (widget.itemCount != oldWidget.itemCount) {
      _heights = List<double>.filled(widget.itemCount, 0, growable: true);
      if (widget.itemCount == 0) {
        _currentPage = 0;
      } else {
        _currentPage = _currentPage.clamp(0, widget.itemCount - 1);
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: _currentHeight,
      child: PageView.builder(
        itemCount: widget.itemCount,
        onPageChanged: (int index) {
          setState(() {
            _currentPage = index;
          });
          widget.onPageChanged?.call(index);
        },
        itemBuilder: (BuildContext context, int index) {
          return OverflowBox(
            alignment: Alignment.topCenter,
            minHeight: 0,
            maxHeight: double.infinity,
            child: _SizeReportingWidget(
              onSizeChange: (Size size) {
                if (index >= _heights.length ||
                    _heights[index] == size.height) {
                  return;
                }
                setState(() {
                  _heights[index] = size.height;
                });
              },
              child: widget.itemBuilder(context, index),
            ),
          );
        },
      ),
    );
  }
}

class _SizeReportingWidget extends StatefulWidget {
  const _SizeReportingWidget({required this.child, required this.onSizeChange});

  final Widget child;
  final ValueChanged<Size> onSizeChange;

  @override
  State<_SizeReportingWidget> createState() => _SizeReportingWidgetState();
}

class _SizeReportingWidgetState extends State<_SizeReportingWidget> {
  Size? _oldSize;

  @override
  Widget build(BuildContext context) {
    WidgetsBinding.instance.addPostFrameCallback((_) => _notifySize());
    return widget.child;
  }

  void _notifySize() {
    if (!mounted) {
      return;
    }
    final size = context.size;
    if (size != null && _oldSize != size) {
      _oldSize = size;
      widget.onSizeChange(size);
    }
  }
}