import 'dart:math' as math;
import 'dart:ui' show Offset;

/// The HUD's pure geometry, kept out of the painters so it can be unit-tested
/// (plan §4: "attitude-ball geometry (bearing/distance → dot position)").
abstract final class HudGeometry {
  static const double _earthRadius = 6371000; // m

  static double _rad(double deg) => deg * math.pi / 180;

  /// Great-circle distance in metres.
  static double distance(double lat1, double lon1, double lat2, double lon2) {
    final double dLat = _rad(lat2 - lat1), dLon = _rad(lon2 - lon1);
    final double h = math.pow(math.sin(dLat / 2), 2) +
        math.cos(_rad(lat1)) * math.cos(_rad(lat2)) * math.pow(math.sin(dLon / 2), 2);
    return 2 * _earthRadius * math.asin(math.min(1, math.sqrt(h)));
  }

  /// Initial bearing from point 1 to point 2, degrees clockwise from north, 0…360.
  static double bearing(double lat1, double lon1, double lat2, double lon2) {
    final double p1 = _rad(lat1), p2 = _rad(lat2), dLon = _rad(lon2 - lon1);
    final double y = math.sin(dLon) * math.cos(p2);
    final double x = math.cos(p1) * math.sin(p2) - math.sin(p1) * math.cos(p2) * math.cos(dLon);
    return (math.atan2(y, x) * 180 / math.pi + 360) % 360;
  }

  /// The attitude ball's distance scales, in metres from centre to rim.
  static const List<double> ballRanges = <double>[25, 50, 100, 200, 500, 1000, 2000, 5000, 10000];

  /// The smallest scale that fits [farthest] on the ball; the largest when nothing does.
  static double ballRange(double farthest) {
    for (final double r in ballRanges) {
      if (farthest <= r) return r;
    }
    return ballRanges.last;
  }

  /// Where a point [distanceM] away at [bearingDeg] lands on a ball of [radius]
  /// px scaled to [rangeM], relative to the centre, with screen y pointing down.
  /// [upDeg] is the bearing drawn at the top: 0 for north-up, the aircraft's
  /// heading for heading-up. Points past the range are pinned to the rim, so
  /// the direction still reads.
  static Offset ballOffset({
    required double bearingDeg,
    required double distanceM,
    required double radius,
    required double rangeM,
    double upDeg = 0,
  }) {
    final double r = radius * (distanceM / rangeM).clamp(0.0, 1.0);
    final double a = _rad(bearingDeg - upDeg);
    return Offset(r * math.sin(a), -r * math.cos(a));
  }

  /// Where the horizon crosses the ball's vertical axis, as a fraction of the
  /// radius from the centre (positive = below centre). As on an artificial
  /// horizon, a nose-down pitch (negative in the SDK) shows more ground, so the
  /// horizon moves *up*; ±[fullScaleDeg] reaches the rim.
  static double horizonShift(double pitchDeg, {double fullScaleDeg = 45}) =>
      (pitchDeg / fullScaleDeg).clamp(-1.0, 1.0);
}

/// Where the smart battery bar draws its fill and markers, as 0…1 fractions of
/// its width. A null marker is one the flight controller has not reported.
class BatteryBarLayout {
  const BatteryBarLayout({required this.fill, this.landMarker, this.homeMarker, this.lowMarker, this.criticalMarker});

  factory BatteryBarLayout.from({
    int? percent,
    int? batteryNeededToLand,
    int? batteryNeededToGoHome,
    int? lowThreshold,
    int? criticalThreshold,
  }) {
    double? f(int? v) => v == null || v <= 0 ? null : (v.clamp(0, 100) / 100.0);
    return BatteryBarLayout(
      fill: (percent ?? 0).clamp(0, 100) / 100.0,
      landMarker: f(batteryNeededToLand),
      homeMarker: f(batteryNeededToGoHome),
      lowMarker: f(lowThreshold),
      criticalMarker: f(criticalThreshold),
    );
  }

  final double fill;

  /// Charge needed to land from the current height.
  final double? landMarker;

  /// Charge needed to fly home and land — GO 4's "H" marker.
  final double? homeMarker;
  final double? lowMarker;
  final double? criticalMarker;

  /// The bar's colour band: 0 = fine, 1 = only enough to go home, 2 = only enough to land.
  int get band {
    if (landMarker != null && fill <= landMarker!) return 2;
    if (criticalMarker != null && fill <= criticalMarker!) return 2;
    if (homeMarker != null && fill <= homeMarker!) return 1;
    if (lowMarker != null && fill <= lowMarker!) return 1;
    return 0;
  }
}

/// `mm:ss`, or `h:mm:ss` past the hour; `--:--` when unknown.
String formatDuration(int? seconds) {
  if (seconds == null || seconds < 0) return '--:--';
  final int h = seconds ~/ 3600, m = (seconds % 3600) ~/ 60, s = seconds % 60;
  final String mm = m.toString().padLeft(2, '0'), ss = s.toString().padLeft(2, '0');
  return h > 0 ? '$h:$mm:$ss' : '$mm:$ss';
}