import 'dart:math'; // Import for sin, cos, atan2, radians

/// Extracts latitude and longitude from a comma-separated string.
///
/// The input string is expected to be in the format "latitude,longitude".
/// For example: "35.8389801,10.5975386"
///
/// Parameters:
///   - [locationString]: The string containing the latitude and longitude.
///
/// Returns:
///   A Map with 'latitude' and 'longitude' as double values, or null
///   if the string format is invalid or parsing fails.
Map<String, double>? extractLatLngFromString(String locationString) {
  final cleanedString = locationString.trim();
  final parts = cleanedString.split(',');

  if (parts.length == 2) {
    try {
      final latitude = double.parse(parts[0].trim());
      final longitude = double.parse(parts[1].trim());
      return {'latitude': latitude, 'longitude': longitude};
    } catch (e) {
      print('Error parsing latitude or longitude from "$locationString": $e');
      return null;
    }
  } else {
    print('Invalid location string format: "$locationString". Expected "latitude,longitude".');
    return null;
  }
}

/// Calculates the distance between a driver's location and a user's location
/// using the Haversine formula.
///
/// This function takes the driver's current location string and the user's
/// start location string (both in "latitude,longitude" format) and
/// returns the great-circle distance between them in kilometers.
///
/// Returns:
///   The distance between the driver and the user in kilometers, or null
///   if either location string is invalid.
double? calculateDistanceBetweenDriverAndUser(
    String driverLocationString,
    String userLocationString,
    ) {
  const double earthRadiusKm = 6371; // Earth's mean radius in kilometers

  // Extract coordinates for the driver
  final Map<String, double>? driverCoords = extractLatLngFromString(driverLocationString);
  if (driverCoords == null) {
    print("Invalid driver location string provided: $driverLocationString");
    return null;
  }
  final double driverLatitude = driverCoords['latitude']!;
  final double driverLongitude = driverCoords['longitude']!;

  // Extract coordinates for the user
  final Map<String, double>? userCoords = extractLatLngFromString(userLocationString);
  if (userCoords == null) {
    print("Invalid user location string provided: $userLocationString");
    return null;
  }
  final double userLatitude = userCoords['latitude']!;
  final double userLongitude = userCoords['longitude']!;

  // Convert degrees to radians
  final double driverLatRad = _toRadians(driverLatitude);
  final double driverLonRad = _toRadians(driverLongitude);
  final double userLatRad = _toRadians(userLatitude);
  final double userLonRad = _toRadians(userLongitude);

  // Differences in coordinates
  final double deltaLat = userLatRad - driverLatRad;
  final double deltaLon = userLonRad - driverLonRad;

  // Haversine formula components
  final double a = pow(sin(deltaLat / 2), 2) +
      cos(driverLatRad) * cos(userLatRad) * pow(sin(deltaLon / 2), 2);
  final double c = 2 * atan2(sqrt(a), sqrt(1 - a));

  // Calculate the distance
  final double distance = earthRadiusKm * c;

  return distance;
}

/// Helper function to convert degrees to radians.
double _toRadians(double degree) {
  return degree * pi / 180;
}