import 'dart:math' as math;

// ---------------------------------------------------------------------------
// Attendance math + filter rules (shared by UI and background service).
//
// Simple version:
//  - Wake every 5 min, take ONE gps reading, sleep again (battery safe).
//  - Throw away weak readings (error > 50 m).
//  - Throw away tiny jumps (< 20 m) so sitting still never invents fake km.
// ---------------------------------------------------------------------------

/// How often the background service takes one GPS reading.
const Duration kFixInterval = Duration(minutes: 5);

/// Max seconds to wait for a single GPS fix before giving up.
const Duration kFixTimeout = Duration(seconds: 30);

/// Discard any fix whose own accuracy error is worse than this (meters).
const double kMaxAcceptableAccuracyMeters = 50.0;

/// Ignore movement smaller than this (meters) - kills stationary drift.
const double kMinMoveMeters = 20.0;

/// Straight-line distance between two lat/lng points, in meters.
double haversineMeters(double lat1, double lon1, double lat2, double lon2) {
  const double earthRadius = 6371000.0; // meters
  final double dLat = _toRadians(lat2 - lat1);
  final double dLon = _toRadians(lon2 - lon1);
  final double a = math.sin(dLat / 2) * math.sin(dLat / 2) +
      math.cos(_toRadians(lat1)) *
          math.cos(_toRadians(lat2)) *
          math.sin(dLon / 2) *
          math.sin(dLon / 2);
  final double c = 2 * math.atan2(math.sqrt(a), math.sqrt(1 - a));
  return earthRadius * c;
}

double _toRadians(double degrees) => degrees * math.pi / 180.0;

/// Decides whether a new fix is worth storing. Returns true only when the
/// reading is strong enough AND the person actually moved.
bool shouldStorePoint({
  required double accuracy,
  required double distanceFromLastMeters,
  required bool isFirstPoint,
}) {
  if (accuracy > kMaxAcceptableAccuracyMeters) return false; // weak signal
  if (!isFirstPoint && distanceFromLastMeters < kMinMoveMeters) {
    return false; // standing still (drift)
  }
  return true;
}