cofounderella/lib/utils/math.dart

import 'dart:math';

import '../models/user_profile.dart';

/// Approximate determination of age
int calcAge(int? birthYear) {
  if (birthYear != null) {
    return (DateTime.now().year - birthYear);
  }
  return 0;
}

/// Returns the approximate age in parentheses,
/// or an empty string if [birthYear] is the current year or null.
String ageInfo(int? birthYear) {
  int age = calcAge(birthYear);
  String ageInfo = age > 0 ? '($age)' : '';
  return ageInfo;
}

///
/// Convert decimal coordinate to degrees minutes seconds (DMS).
///
String convertDecimalToDMS(double decimalValue, {required bool isLatitude}) {
  bool isNegative = decimalValue < 0;
  double absoluteValue = decimalValue.abs();

  int degrees = absoluteValue.toInt();
  double minutesDecimal = (absoluteValue - degrees) * 60;
  int minutes = minutesDecimal.toInt();
  double secondsDecimal = (minutesDecimal - minutes) * 60;
  double seconds = double.parse(secondsDecimal.toStringAsFixed(2));

  String direction;
  if (isLatitude) {
    direction = isNegative ? 'S' : 'N';
  } else {
    direction = isNegative ? 'W' : 'E';
  }

  // return formatted string
  return '${degrees.abs()}° ${minutes.abs()}\' ${seconds.abs().toStringAsFixed(2)}" $direction';
}

///
/// Distance in kilometers between two location coordinates
///
double calculateDistance(double lat1, double lon1, double lat2, double lon2) {
  const R = 6371; // earth radius in kilometers

  // distance between latitudes and longitudes
  final dLat = _degreesToRadians(lat2 - lat1);
  final dLon = _degreesToRadians(lon2 - lon1);

  final a = sin(dLat / 2) * sin(dLat / 2) +
      cos(_degreesToRadians(lat1)) *
          cos(_degreesToRadians(lat2)) *
          sin(dLon / 2) *
          sin(dLon / 2);
  final c = 2 * atan2(sqrt(a), sqrt(1 - a));

  return R * c;
}

double _degreesToRadians(double degrees) {
  return degrees * pi / 180;
}

///
/// Shortest distance between two users locations
///
double shortestDistanceBetweenUsers(
    UserProfile currentUser, UserProfile otherUser) {
  try {
    if (currentUser.locations.isEmpty || otherUser.locations.isEmpty) {
      return double.nan;
    }

    double shortestDistance = double.nan;
    // locations currentUser
    for (var loc1 in currentUser.locations.values) {
      if (loc1 != null && loc1.latitude != null && loc1.longitude != null) {
        for (var loc2 in otherUser.locations.values) {
          if (loc2 != null && loc2.latitude != null && loc2.longitude != null) {
            double distance = calculateDistance(loc1.latitude!, loc1.longitude!,
                loc2.latitude!, loc2.longitude!);
            if (shortestDistance.isNaN || distance < shortestDistance) {
              shortestDistance = distance;
            }
          }
        }
      }
    }

    return shortestDistance;
  } catch (e) {
    return double.nan;
  }
}