import 'dart:math' as math;

import 'package:flutter/material.dart';
import 'package:latlong2/latlong.dart' hide Path;

import '../../domain/waypoint/flat_waypoint_list.dart';

/// Vollbild-Chart zum Anpassen von Hoehe/Geschwindigkeit per Drag auf den
/// Punkten (HTML-Demonstrator: buildFullChart()/attachChartDrag()). Jeder
/// Punkt entspricht einem Wegpunkt, X-Position proportional zur
/// zurueckgelegten Distanz entlang der Route.
///
/// Terrain-Overlay und Wind-Diamanten aus dem Demonstrator sind nicht
/// portiert, da Terrain- (Doku 3.9) und Wind-System (Doku 3.8) in der
/// Flutter-App noch nicht existieren.
class FullValueChart extends StatefulWidget {
  const FullValueChart({
    super.key,
    required this.waypoints,
    required this.values,
    required this.legBad,
    required this.vertexBad,
    required this.activeIndex,
    required this.min,
    required this.max,
    required this.step,
    required this.pxPerUnit,
    required this.unit,
    required this.onChanged,
  });

  final List<Waypoint> waypoints;
  final List<double> values;
  final List<bool> legBad;
  final List<bool> vertexBad;
  final int activeIndex;
  final double min;
  final double max;
  final double step;
  final double pxPerUnit;
  final String unit;
  final void Function(int index, double value) onChanged;

  static const _distance = Distance(roundResult: false);

  static List<double> cumulativeDistances(List<Waypoint> waypoints) {
    final cum = <double>[0];
    for (var i = 1; i < waypoints.length; i++) {
      final a = LatLng(waypoints[i - 1].lat, waypoints[i - 1].lon);
      final b = LatLng(waypoints[i].lat, waypoints[i].lon);
      cum.add(cum[i - 1] + _distance(a, b));
    }
    return cum;
  }

  @override
  State<FullValueChart> createState() => _FullValueChartState();
}

class _FullValueChartState extends State<FullValueChart> {
  int? _dragIndex;
  double _dragStartY = 0;
  double _dragStartValue = 0;

  static const _padX = 50.0;
  static const _hitToleranceX = 28.0;

  ({double lo, double hi}) _range() {
    if (widget.values.isEmpty) return (lo: widget.min, hi: widget.max);
    final dataMin = widget.values.reduce(math.min);
    final dataMax = widget.values.reduce(math.max);
    final span = dataMax - dataMin;
    final pad = math.max(span * 0.35, widget.step * 2);
    var lo = dataMin - pad;
    var hi = dataMax + pad;
    final minSpan = widget.step * 6;
    if (hi - lo < minSpan) {
      final mid = (lo + hi) / 2;
      lo = mid - minSpan / 2;
      hi = mid + minSpan / 2;
    }
    if (lo < widget.min) lo = widget.min;
    if (hi > widget.max) hi = widget.max;
    if (hi <= lo) {
      lo = widget.min;
      hi = widget.max;
    }
    return (lo: lo, hi: hi);
  }

  double _xAt(int idx, List<double> cumDist, double boxW) {
    final n = widget.waypoints.length;
    if (n <= 1) return boxW / 2;
    final total = cumDist.last == 0 ? 1.0 : cumDist.last;
    return _padX + (cumDist[idx] / total) * (boxW - 2 * _padX);
  }

  int? _nearestIndex(Offset local, List<double> cumDist, double boxW) {
    var best = -1;
    var bestDist = double.infinity;
    for (var i = 0; i < widget.waypoints.length; i++) {
      final dx = (_xAt(i, cumDist, boxW) - local.dx).abs();
      if (dx < bestDist) {
        bestDist = dx;
        best = i;
      }
    }
    return bestDist <= _hitToleranceX ? best : null;
  }

  @override
  Widget build(BuildContext context) {
    if (widget.waypoints.isEmpty) {
      return const Center(
        child: Text('No waypoints yet', style: TextStyle(color: Colors.white60)),
      );
    }

    final cumDist = FullValueChart.cumulativeDistances(widget.waypoints);
    final range = _range();

    return LayoutBuilder(
      builder: (context, constraints) {
        final size = Size(constraints.maxWidth, constraints.maxHeight);
        return GestureDetector(
          onPanStart: (details) {
            final idx = _nearestIndex(details.localPosition, cumDist, size.width);
            if (idx == null) return;
            _dragIndex = idx;
            _dragStartY = details.localPosition.dy;
            _dragStartValue = widget.values[idx];
          },
          onPanUpdate: (details) {
            final idx = _dragIndex;
            if (idx == null) return;
            final deltaY = _dragStartY - details.localPosition.dy;
            final deltaVal = deltaY / widget.pxPerUnit;
            var val = _dragStartValue + deltaVal;
            val = (val / widget.step).round() * widget.step;
            val = val.clamp(widget.min, widget.max);
            widget.onChanged(idx, val);
          },
          onPanEnd: (_) => _dragIndex = null,
          onPanCancel: () => _dragIndex = null,
          child: CustomPaint(
            size: size,
            painter: _ChartPainter(
              waypoints: widget.waypoints,
              values: widget.values,
              cumDist: cumDist,
              legBad: widget.legBad,
              vertexBad: widget.vertexBad,
              activeIndex: widget.activeIndex,
              lo: range.lo,
              hi: range.hi,
              unit: widget.unit,
            ),
          ),
        );
      },
    );
  }
}

class _ChartPainter extends CustomPainter {
  const _ChartPainter({
    required this.waypoints,
    required this.values,
    required this.cumDist,
    required this.legBad,
    required this.vertexBad,
    required this.activeIndex,
    required this.lo,
    required this.hi,
    required this.unit,
  });

  final List<Waypoint> waypoints;
  final List<double> values;
  final List<double> cumDist;
  final List<bool> legBad;
  final List<bool> vertexBad;
  final int activeIndex;
  final double lo;
  final double hi;
  final String unit;

  static const _padX = 50.0;
  static const _padY = 20.0;

  double _xAt(int idx, double boxW) {
    final n = waypoints.length;
    if (n <= 1) return boxW / 2;
    final total = cumDist.last == 0 ? 1.0 : cumDist.last;
    return _padX + (cumDist[idx] / total) * (boxW - 2 * _padX);
  }

  double _yAt(double val, double boxH) =>
      boxH - _padY - ((val - lo) / (hi - lo)) * (boxH - 2 * _padY);

  double _niceStep(double range, int targetTicks) {
    if (range <= 0) return 1;
    final rough = range / targetTicks;
    final mag = math.pow(10, (math.log(rough) / math.ln10).floor()).toDouble();
    final norm = rough / mag;
    if (norm < 1.5) return mag;
    if (norm < 3) return 2 * mag;
    if (norm < 7) return 5 * mag;
    return 10 * mag;
  }

  @override
  void paint(Canvas canvas, Size size) {
    final boxW = size.width;
    final boxH = size.height;
    final n = waypoints.length;

    // Gridlines mit gerundeten Werten.
    final step = _niceStep(hi - lo, 5);
    final gridPaint = Paint()
      ..color = Colors.white.withValues(alpha: 0.14)
      ..strokeWidth = 1;
    final axisPaint = Paint()
      ..color = Colors.white.withValues(alpha: 0.35)
      ..strokeWidth = 1.5;
    canvas.drawLine(Offset(_padX, 0), Offset(_padX, boxH), axisPaint);

    final labelStyle = TextStyle(color: Colors.white.withValues(alpha: 0.6), fontSize: 10);
    var v = (lo / step).ceil() * step;
    while (v <= hi + 1e-6) {
      final y = _yAt(v, boxH);
      canvas.drawLine(Offset(_padX, y), Offset(boxW - _padX, y), gridPaint);
      final tp = TextPainter(
        text: TextSpan(text: '${v.round()}$unit', style: labelStyle),
        textDirection: TextDirection.ltr,
      )..layout();
      tp.paint(canvas, Offset(_padX - 8 - tp.width, y - tp.height / 2));
      v += step;
    }

    // Verbindungslinien (rot bei nicht fliegbarer Steig-/Sinkrate).
    for (var i = 0; i < n - 1; i++) {
      final bad = i < legBad.length && legBad[i];
      canvas.drawLine(
        Offset(_xAt(i, boxW), _yAt(values[i], boxH)),
        Offset(_xAt(i + 1, boxW), _yAt(values[i + 1], boxH)),
        Paint()
          ..color = bad ? const Color(0xFFE2574A) : Colors.white
          ..strokeWidth = 2.5,
      );
    }

    // Punkte (blau=aktiver Zielpunkt, rot=nicht fliegbar, sonst weiss).
    for (var i = 0; i < n; i++) {
      final active = i == activeIndex;
      final bad = i < vertexBad.length && vertexBad[i];
      final color =
          active ? const Color(0xFF4D9DFF) : (bad ? const Color(0xFFE2574A) : Colors.white);
      final center = Offset(_xAt(i, boxW), _yAt(values[i], boxH));
      canvas.drawCircle(center, active ? 9 : 7, Paint()..color = color);
      canvas.drawCircle(
        center,
        active ? 9 : 7,
        Paint()
          ..color = const Color(0xFF2F6FE0)
          ..style = PaintingStyle.stroke
          ..strokeWidth = 2,
      );
    }
  }

  @override
  bool shouldRepaint(covariant _ChartPainter oldDelegate) =>
      oldDelegate.values != values ||
      oldDelegate.activeIndex != activeIndex ||
      oldDelegate.lo != lo ||
      oldDelegate.hi != hi;
}