import 'package:flutter/material.dart';

/// 「加入购物车」式飞行动画：把某个组件的副本从原位置缩小飞到目标位置。
///
/// 挂在 Overlay 上而不是弹窗内部——先测量、再关弹窗、最后飞，这样蒙层干净消失，
/// 飞行层浮在真实页面之上；放弹窗里做的话背景遮罩会一直压着，不像"收进去"。
class FlyToOverlay {
  FlyToOverlay._();

  /// [context] 调用方(弹窗)的 context，用来找根 Overlay —— 不能用 Get.overlayContext，
  /// 那拿到的是 Overlay 自身的 context，而 Overlay.of 只往祖先找，必然抛 "No Overlay widget found"
  /// [sourceKey] 起飞组件（**必须在关闭弹窗前调用**，否则拿不到位置）
  /// [target] 目标区域（屏幕坐标）；[child] 飞行途中显示的内容，通常是起飞组件的副本
  static void play({
    required BuildContext context,
    required GlobalKey sourceKey,
    required Rect target,
    required Widget child,
    Duration duration = const Duration(milliseconds: 700),
  }) {
    final box = sourceKey.currentContext?.findRenderObject() as RenderBox?;
    if (box == null || !box.hasSize) return; // 量不到就不飞，不能因为动画报错
    final begin = box.localToGlobal(Offset.zero) & box.size;

    // rootOverlay：挂到最顶层，弹窗 pop 掉之后飞行层还得继续存活
    final overlay = Overlay.maybeOf(context, rootOverlay: true);
    if (overlay == null) return;

    late OverlayEntry entry;
    entry = OverlayEntry(
      builder: (_) => _FlyView(
        begin: begin,
        end: target,
        duration: duration,
        // Overlay 被整体销毁时 entry 已不在树上，再 remove 会踩 assert
        onDone: () {
          if (entry.mounted) entry.remove();
        },
        child: child,
      ),
    );
    overlay.insert(entry);
  }
}

class _FlyView extends StatefulWidget {
  final Rect begin;
  final Rect end;
  final Duration duration;
  final VoidCallback onDone;
  final Widget child;

  const _FlyView({
    required this.begin,
    required this.end,
    required this.duration,
    required this.onDone,
    required this.child,
  });

  @override
  State<_FlyView> createState() => _FlyViewState();
}

class _FlyViewState extends State<_FlyView> with SingleTickerProviderStateMixin {
  late final AnimationController _ctr = AnimationController(vsync: this, duration: widget.duration);

  // easeInOutCubic：起步慢、中段快、**末尾减速**。不用 easeIn 系是因为那样末尾越飞越快，
  // 到落点时一闪而过，用户来不及把弹窗和浮窗对应起来
  late final Animation<Rect?> _rect = RectTween(begin: widget.begin, end: widget.end)
      .animate(CurvedAnimation(parent: _ctr, curve: Curves.easeInOutCubic));

  @override
  void initState() {
    super.initState();
    _ctr.addStatusListener((s) {
      if (s == AnimationStatus.completed) widget.onDone();
    });
    _ctr.forward();
  }

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

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: _ctr,
      builder: (_, child) {
        final r = _rect.value ?? widget.begin;
        // 全程基本保持不透明，只在最后 12% 收尾淡出：太早淡出会让人看不清落到哪儿了
        final t = _ctr.value;
        final opacity = t < 0.88 ? 1.0 : (1 - (t - 0.88) / 0.12).clamp(0.0, 1.0);
        return Positioned(
          left: r.left,
          top: r.top,
          width: r.width,
          height: r.height,
          child: IgnorePointer(
            child: Opacity(opacity: opacity, child: child),
          ),
        );
      },
      // 内容按起飞尺寸渲染一次，交给 FittedBox 等比缩放，避免每帧重新布局图片
      child: FittedBox(
        fit: BoxFit.fill,
        child: SizedBox(
          width: widget.begin.width,
          height: widget.begin.height,
          child: widget.child,
        ),
      ),
    );
  }
}