import 'dart:ui';

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

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

/// A frosted-glass segmented control for use on the brand header.
///
/// The track is translucent and blurs whatever sits behind it, with a bright
/// top edge and a darker bottom edge so it reads as a pane of glass rather
/// than a flat tint. The selected segment is a brighter frosted pill that
/// slides between positions.
class GlassSegments<T> extends StatelessWidget {
  const GlassSegments({
    super.key,
    required this.segments,
    required this.value,
    required this.onChanged,
    this.height = 44,
  });

  /// Each segment as `(value, label)`.
  final List<(T, String)> segments;
  final T value;
  final ValueChanged<T> onChanged;
  final double height;

  static const _radius = 15.0;
  static const _pad = 4.0;

  @override
  Widget build(BuildContext context) {
    final index = segments.indexWhere((s) => s.$1 == value);

    return SizedBox(
      height: height,
      child: ClipRRect(
        borderRadius: BorderRadius.circular(_radius),
        child: BackdropFilter(
          filter: ImageFilter.blur(sigmaX: 16, sigmaY: 16),
          child: Container(
            decoration: BoxDecoration(
              borderRadius: BorderRadius.circular(_radius),
              // Light falling across the pane: brighter at the top edge.
              gradient: LinearGradient(
                begin: Alignment.topLeft,
                end: Alignment.bottomRight,
                colors: [
                  Colors.white.withValues(alpha: 0.26),
                  Colors.white.withValues(alpha: 0.12),
                ],
              ),
              border: Border.all(
                color: Colors.white.withValues(alpha: 0.28),
                width: 1,
              ),
            ),
            padding: const EdgeInsets.all(_pad),
            child: LayoutBuilder(
              builder: (context, constraints) {
                final segmentWidth = constraints.maxWidth / segments.length;

                // One animation drives everything: the pill's position, its
                // stretch, and each label's colour. Animating the selected
                // index as a double — rather than moving the pill and flipping
                // the labels separately — is what makes the labels light up
                // exactly as the pill arrives over them. Retargeting mid-flight
                // continues from wherever the pill currently is.
                return TweenAnimationBuilder<double>(
                  tween: Tween(end: index.toDouble()),
                  duration: const Duration(milliseconds: 340),
                  curve: Curves.easeOutQuint,
                  builder: (context, position, _) {
                    // Squash and stretch: the pill widens at speed and settles
                    // back to size as it lands.
                    final travel = (position - position.roundToDouble()).abs();
                    final stretch = segmentWidth * 0.12 * (travel * 2);

                    return Stack(
                      children: [
                        if (index >= 0)
                          Positioned(
                            left: position * segmentWidth - stretch / 2,
                            width: segmentWidth + stretch,
                            top: 0,
                            bottom: 0,
                            child: const _SelectedPill(),
                          ),
                        Row(
                          children: [
                            for (var i = 0; i < segments.length; i++)
                              Expanded(
                                child: _Segment(
                                  label: segments[i].$2,
                                  // 1 when the pill is centred on this label,
                                  // 0 once it has moved a full segment away.
                                  selectedAmount: (1 - (position - i).abs())
                                      .clamp(0.0, 1.0),
                                  onTap: () {
                                    if (segments[i].$1 == value) return;
                                    HapticFeedback.selectionClick();
                                    onChanged(segments[i].$1);
                                  },
                                ),
                              ),
                          ],
                        ),
                      ],
                    );
                  },
                );
              },
            ),
          ),
        ),
      ),
    );
  }
}

class _SelectedPill extends StatelessWidget {
  const _SelectedPill();

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(11),
        gradient: LinearGradient(
          begin: Alignment.topCenter,
          end: Alignment.bottomCenter,
          colors: [
            Colors.white.withValues(alpha: 0.96),
            Colors.white.withValues(alpha: 0.86),
          ],
        ),
        border: Border.all(color: Colors.white.withValues(alpha: 0.9)),
        boxShadow: [
          BoxShadow(
            color: KrowPalette.blueDeep.withValues(alpha: 0.28),
            blurRadius: 12,
            offset: const Offset(0, 4),
          ),
        ],
      ),
    );
  }
}

class _Segment extends StatelessWidget {
  const _Segment({
    required this.label,
    required this.selectedAmount,
    required this.onTap,
  });

  final String label;

  /// How far the travelling pill has arrived over this label, 0 to 1.
  final double selectedAmount;
  final VoidCallback onTap;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      behavior: HitTestBehavior.opaque,
      onTap: onTap,
      child: Center(
        child: Text(
          label,
          maxLines: 1,
          overflow: TextOverflow.ellipsis,
          style: TextStyle(
            fontSize: 12.5,
            // Weight is snapped to the nearest real weight; the eye reads the
            // colour ramp as the smooth part.
            fontWeight: selectedAmount > 0.5
                ? FontWeight.w700
                : FontWeight.w600,
            color: Color.lerp(
              Colors.white.withValues(alpha: 0.82),
              KrowPalette.blue,
              Curves.easeIn.transform(selectedAmount),
            ),
          ),
        ),
      ),
    );
  }
}