// Author: fruit.com.cn

import 'package:flutter/material.dart';

import '../../../core/theme/app_colors.dart';
import '../../../core/theme/app_dimens.dart';

const double _maxPull = 96;
const double _refreshThreshold = 56;
const double _firstPageEpsilon = 0.01;

/// 第一条已经到顶时，向下的拖动不再翻页。
class FeedRefreshPhysics extends PageScrollPhysics {
  const FeedRefreshPhysics({super.parent});

  @override
  FeedRefreshPhysics applyTo(ScrollPhysics? ancestor) {
    return FeedRefreshPhysics(parent: buildParent(ancestor));
  }

  @override
  double applyPhysicsToUserOffset(ScrollMetrics position, double offset) {
    if (position.pixels <= position.minScrollExtent && offset > 0) {
      return 0;
    }
    return super.applyPhysicsToUserOffset(position, offset);
  }

  @override
  Simulation? createBallisticSimulation(
    ScrollMetrics position,
    double velocity,
  ) {
    if (position.pixels <= position.minScrollExtent && velocity < 0) {
      return super.createBallisticSimulation(position, 0);
    }
    return super.createBallisticSimulation(position, velocity);
  }
}

/// 竖滑到第一条后继续下拉时刷新，其它页仍交给翻页。
class FeedPullRefresh extends StatefulWidget {
  const FeedPullRefresh({
    super.key,
    required this.pageController,
    required this.onRefresh,
    required this.child,
    this.topInset = 0,
  });

  final PageController pageController;
  final Future<void> Function() onRefresh;
  final Widget child;
  final double topInset;

  @override
  State<FeedPullRefresh> createState() => _FeedPullRefreshState();
}

class _FeedPullRefreshState extends State<FeedPullRefresh> {
  Offset? _origin;
  double _pull = 0;
  bool _tracking = false;
  bool _refreshing = false;

  bool _atFirstPage() {
    final controller = widget.pageController;
    if (!controller.hasClients) return false;
    return (controller.page ?? 0) <= _firstPageEpsilon;
  }

  void _setPull(double value) {
    final next = value.clamp(0.0, _maxPull);
    if (next == _pull) return;
    setState(() => _pull = next);
  }

  void _onPointerDown(PointerDownEvent event) {
    if (_refreshing || !_atFirstPage()) {
      _tracking = false;
      return;
    }
    _origin = event.position;
    _tracking = true;
  }

  void _onPointerMove(PointerMoveEvent event) {
    final origin = _origin;
    if (!_tracking || origin == null || _refreshing) return;
    final delta = event.position - origin;
    if (delta.dx.abs() > delta.dy.abs() && delta.dy < _refreshThreshold) {
      _tracking = false;
      _setPull(0);
      return;
    }
    if (delta.dy > 0) _holdFirstPage();
    _setPull(delta.dy);
  }

  void _holdFirstPage() {
    final controller = widget.pageController;
    if (!controller.hasClients) return;
    final position = controller.position;
    if (position.pixels <= position.minScrollExtent) return;
    controller.jumpTo(position.minScrollExtent);
  }

  void _onPointerEnd() {
    final shouldRefresh = _tracking && _pull >= _refreshThreshold;
    _origin = null;
    _tracking = false;
    if (shouldRefresh) {
      _refresh();
      return;
    }
    _setPull(0);
  }

  Future<void> _refresh() async {
    if (_refreshing) return;
    _refreshing = true;
    _setPull(_refreshThreshold);
    try {
      await widget.onRefresh();
    } finally {
      _refreshing = false;
      if (mounted) _setPull(0);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Listener(
      onPointerDown: _onPointerDown,
      onPointerMove: _onPointerMove,
      onPointerUp: (_) => _onPointerEnd(),
      onPointerCancel: (_) => _onPointerEnd(),
      child: Stack(
        fit: StackFit.expand,
        children: [
          widget.child,
          if (_pull > 0)
            Positioned(
              top: widget.topInset,
              left: 0,
              right: 0,
              child: IgnorePointer(
                child: Align(
                  alignment: Alignment.topCenter,
                  child: Container(
                    key: const Key('pull-refresh-indicator'),
                    width: AppDimens.refreshIndicatorSize,
                    height: AppDimens.refreshIndicatorSize,
                    padding: const EdgeInsets.all(
                      (AppDimens.refreshIndicatorSize -
                              AppDimens.refreshSpinnerSize) /
                          2,
                    ),
                    decoration: BoxDecoration(
                      color: AppColors.refreshIndicatorSurface,
                      borderRadius: BorderRadius.circular(
                        AppDimens.refreshIndicatorRadius,
                      ),
                    ),
                    child: const SizedBox.square(
                      dimension: AppDimens.refreshSpinnerSize,
                      child: CircularProgressIndicator(
                        strokeWidth: AppDimens.refreshSpinnerStroke,
                        color: AppColors.textPrimary,
                      ),
                    ),
                  ),
                ),
              ),
            ),
        ],
      ),
    );
  }
}