import 'package:flutter/material.dart';

/// Retains all tab states and scroll positions, with no page-swipe recognizer.
class TabDeck extends StatefulWidget {
  const TabDeck({super.key, required this.index, required this.children});
  final int index;
  final List<Widget> children;
  @override
  State<TabDeck> createState() => _TabDeckState();
}

class _TabDeckState extends State<TabDeck> with SingleTickerProviderStateMixin {
  late final AnimationController _motion = AnimationController(
    vsync: this,
    duration: const Duration(milliseconds: 330),
    value: 1,
  );
  int? _outgoing;
  int _direction = 1;
  @override
  void didUpdateWidget(TabDeck oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.index != widget.index) {
      _outgoing = oldWidget.index;
      _direction = widget.index > oldWidget.index ? 1 : -1;
      if (MediaQuery.disableAnimationsOf(context)) {
        _motion.value = 1;
      } else {
        _motion.forward(from: 0);
      }
    }
  }

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

  @override
  Widget build(BuildContext context) => AnimatedBuilder(
    animation: _motion,
    builder: (context, _) {
      final t = Curves.easeOutCubic.transform(_motion.value);
      return Stack(
        fit: StackFit.expand,
        children: [
          for (var i = 0; i < widget.children.length; i++)
            Offstage(
              offstage:
                  i != widget.index && (i != _outgoing || _motion.isCompleted),
              child: TickerMode(
                enabled: i == widget.index,
                child: IgnorePointer(
                  ignoring: i != widget.index,
                  child: ExcludeSemantics(
                    excluding: i != widget.index,
                    child: Opacity(
                      opacity: i == widget.index
                          ? t
                          : (i == _outgoing ? 1 - t : 0),
                      child: Transform.translate(
                        offset: Offset(
                          (i == widget.index ? 1 - t : -t) * 22 * _direction,
                          0,
                        ),
                        child: widget.children[i],
                      ),
                    ),
                  ),
                ),
              ),
            ),
        ],
      );
    },
  );
}