import 'package:flutter/material.dart';

/// Moves the week body without adding a second horizontal scroll surface.
/// Rapid requests are coalesced to the latest week after the current movement.
class DirectionalWeekTransition extends StatefulWidget {
  const DirectionalWeekTransition({
    super.key,
    required this.week,
    required this.child,
  });

  final int week;
  final Widget child;

  @override
  State<DirectionalWeekTransition> createState() =>
      _DirectionalWeekTransitionState();
}

class _DirectionalWeekTransitionState extends State<DirectionalWeekTransition>
    with SingleTickerProviderStateMixin {
  late final AnimationController _motion = AnimationController(
    vsync: this,
    duration: const Duration(milliseconds: 280),
    value: 1,
  )..addStatusListener(_onStatus);
  late Widget _incoming;
  Widget? _outgoing;
  late int _incomingWeek;
  double _direction = 1;
  bool _reduceMotion = false;

  @override
  void initState() {
    super.initState();
    _incoming = widget.child;
    _incomingWeek = widget.week;
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    _reduceMotion = MediaQuery.disableAnimationsOf(context);
    if (_reduceMotion) _snap();
  }

  void _snap() {
    _motion.stop();
    _outgoing = null;
    _incoming = widget.child;
    _incomingWeek = widget.week;
    _motion.value = 1;
  }

  void _start() {
    _outgoing = _incoming;
    _direction = widget.week > _incomingWeek ? 1 : -1;
    _incoming = widget.child;
    _incomingWeek = widget.week;
    _motion.forward(from: 0);
  }

  @override
  void didUpdateWidget(DirectionalWeekTransition oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (_reduceMotion) {
      _snap();
    } else if (widget.week == _incomingWeek) {
      _incoming = widget.child;
    } else if (!_motion.isAnimating) {
      _start();
    }
    // While moving, widget holds the latest request. Do not restart a tween or
    // accumulate outgoing grids every time another swipe/arrow arrives.
  }

  void _onStatus(AnimationStatus status) {
    if (status != AnimationStatus.completed ||
        !mounted ||
        _reduceMotion ||
        _outgoing == null) {
      return;
    }
    setState(() {
      _outgoing = null;
      if (widget.week != _incomingWeek) _start();
    });
  }

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

  @override
  Widget build(BuildContext context) => ClipRect(
    child: AnimatedBuilder(
      animation: _motion,
      builder: (context, _) {
        final progress = Curves.easeInOutCubic.transform(_motion.value);
        final stale = widget.week != _incomingWeek;
        return Stack(
          alignment: Alignment.topLeft,
          children: [
            if (_outgoing != null)
              ExcludeSemantics(
                child: ExcludeFocus(
                  child: IgnorePointer(
                    child: FractionalTranslation(
                      key: const Key('week-transition-outgoing'),
                      translation: Offset(-_direction * 0.08 * progress, 0),
                      child: Opacity(opacity: 1 - progress, child: _outgoing),
                    ),
                  ),
                ),
              ),
            ExcludeSemantics(
              excluding: stale,
              child: ExcludeFocus(
                excluding: stale,
                child: IgnorePointer(
                  ignoring: stale,
                  child: FractionalTranslation(
                    key: const Key('week-transition-incoming'),
                    translation: Offset(_direction * 0.08 * (1 - progress), 0),
                    child: Opacity(opacity: progress, child: _incoming),
                  ),
                ),
              ),
            ),
          ],
        );
      },
    ),
  );
}