import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

/// The full-screen "spotlight" shown by one step of the first-launch
/// guided tour: a dimmed barrier with a cut-out hole around each of
/// [targetKeys]' current on-screen positions (or, for any key that isn't
/// laid out yet / doesn't resolve, no hole for it — falling back to a
/// plain dimmed barrier with the card centered if none resolve), plus a
/// card explaining the step with Next/Skip controls. Most steps highlight
/// a single element, but [targetKeys] can hold more than one — e.g. the
/// first step highlights both the "+" button and the Receipts tab it
/// lives on, together.
///
/// This widget is purely presentational — it doesn't know about tabs,
/// routes, or persistence. `MainShell` is responsible for sequencing
/// steps, navigating to the right screen/route before each one, and
/// recording that the tour's been seen once it ends.
class OnboardingTourOverlay extends StatelessWidget {
  final List<GlobalKey> targetKeys;
  final String title;
  final String description;
  final int stepNumber;
  final int totalSteps;
  final VoidCallback onNext;
  final VoidCallback onSkip;

  const OnboardingTourOverlay({
    super.key,
    required this.targetKeys,
    required this.title,
    required this.description,
    required this.stepNumber,
    required this.totalSteps,
    required this.onNext,
    required this.onSkip,
  });

  List<Rect> _targetRects() {
    final rects = <Rect>[];
    for (final key in targetKeys) {
      final renderObject = key.currentContext?.findRenderObject();
      if (renderObject is RenderBox && renderObject.hasSize) {
        rects.add((renderObject.localToGlobal(Offset.zero) & renderObject.size).inflate(6));
      }
    }
    return rects;
  }

  @override
  Widget build(BuildContext context) {
    final rects = _targetRects();
    final media = MediaQuery.of(context);
    final isLastStep = stepNumber >= totalSteps;
    final colorScheme = Theme.of(context).colorScheme;

    final screenMid = media.size.height / 2;
    final topGroup = rects.where((r) => r.center.dy < screenMid);
    final bottomGroup = rects.where((r) => r.center.dy >= screenMid);

    double? cardTop;
    double? cardBottom;
    if (topGroup.isNotEmpty && bottomGroup.isNotEmpty) {
      // Highlighted elements exist both above and below the screen's
      // midpoint (e.g. an AppBar action + a bottom-nav destination) — the
      // union of every rect would span almost the full screen height in
      // this case, which the plain below/above logic below handles badly.
      // Anchor the card just under the topmost group instead, into the
      // open band between the two.
      cardTop = topGroup.map((r) => r.bottom).reduce((a, b) => a > b ? a : b) + 16;
    } else {
      final unionRect = rects.isEmpty ? null : rects.reduce((a, b) => a.expandToInclude(b));
      // Prefer placing the card below the highlighted element(s); only
      // flip above if there's not enough room below on this screen.
      final cardBelow = unionRect == null || (unionRect.bottom + 260) < media.size.height;
      if (cardBelow) {
        cardTop = (unionRect?.bottom ?? media.size.height * 0.38) + 16;
      } else {
        cardBottom = media.size.height - unionRect.top + 16;
      }
    }

    return Stack(
      children: [
        Positioned.fill(
          child: GestureDetector(
            behavior: HitTestBehavior.opaque,
            // Swallows every tap on the barrier (and the spotlight holes
            // themselves) so a highlighted element can't be accidentally
            // triggered mid-tour — Next/Skip on the card are the only way
            // to advance.
            onTap: () {},
            child: CustomPaint(
              painter: _SpotlightPainter(
                targetRects: rects,
                color: Colors.black.withValues(alpha: 0.75),
              ),
            ),
          ),
        ),
        for (final rect in rects)
          Positioned(
            left: rect.left,
            top: rect.top,
            width: rect.width,
            height: rect.height,
            child: IgnorePointer(
              child: DecoratedBox(
                decoration: BoxDecoration(
                  border: Border.all(color: colorScheme.primary, width: 2.5),
                  borderRadius: BorderRadius.circular(12),
                ),
              ),
            ),
          ),
        Positioned(
          left: 20,
          right: 20,
          top: cardTop,
          bottom: cardBottom,
          child: SafeArea(
            child: Card(
              elevation: 8,
              child: Padding(
                padding: const EdgeInsets.all(20),
                child: Column(
                  mainAxisSize: MainAxisSize.min,
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Text(
                      'Step $stepNumber of $totalSteps',
                      style: Theme.of(context).textTheme.labelMedium?.copyWith(
                            color: colorScheme.primary,
                            fontWeight: FontWeight.w700,
                          ),
                    ),
                    const SizedBox(height: 6),
                    Text(title, style: Theme.of(context).textTheme.titleLarge),
                    const SizedBox(height: 8),
                    Text(description, style: Theme.of(context).textTheme.bodyMedium),
                    const SizedBox(height: 20),
                    Row(
                      mainAxisAlignment: MainAxisAlignment.spaceBetween,
                      children: [
                        TextButton(onPressed: onSkip, child: const Text('Skip Tour')),
                        FilledButton(onPressed: onNext, child: Text(isLastStep ? 'Got It' : 'Next')),
                      ],
                    ),
                  ],
                ),
              ),
            ),
          ),
        ),
      ],
    );
  }
}

class _SpotlightPainter extends CustomPainter {
  final List<Rect> targetRects;
  final Color color;

  const _SpotlightPainter({required this.targetRects, required this.color});

  @override
  void paint(Canvas canvas, Size size) {
    final barrierPaint = Paint()..color = color;
    var path = Path()..addRect(Offset.zero & size);
    for (final rect in targetRects) {
      final holePath = Path()..addRRect(RRect.fromRectAndRadius(rect, const Radius.circular(12)));
      path = Path.combine(PathOperation.difference, path, holePath);
    }
    canvas.drawPath(path, barrierPaint);
  }

  @override
  bool shouldRepaint(covariant _SpotlightPainter oldDelegate) =>
      !listEquals(oldDelegate.targetRects, targetRects) || oldDelegate.color != color;
}