////////////////////////////////////////////////////////////////////////////////
///                                                                          ///
///  This routine calculates the distance between two points (given the      ///
///  latitude/longitude of those points). It is being used to calculate      ///
///  the distance between two location using GeoDataSource(TM)               ///
///  products.                                                               ///
///                                                                          ///
///  Definitions:                                                            ///
///    South latitudes are negative, east longitudes are positive            ///
///                                                                          ///
///  Passed to function:                                                     ///
///    lat1, lon1 = Latitude and Longitude of point 1 (in decimal degrees)   ///
///    lat2, lon2 = Latitude and Longitude of point 2 (in decimal degrees)   ///
///    unit = the unit you desire for results                                ///
///           where: 'M' is statute miles (default)                          ///
///                  'K' is kilometers                                       ///
///                  'N' is nautical miles                                   ///
///                                                                          ///
///  Worldwide cities and other features databases with latitude longitude   ///
///  are available at https://www.geodatasource.com                          ///
///                                                                          ///
///  For enquiries, please contact sales@geodatasource.com                   ///
///                                                                          ///
///  Official Web site: https://www.geodatasource.com                        ///
///                                                                          ///
///  GeoDataSource.com (C) All Rights Reserved 2022                          ///
///                                                                          ///
////////////////////////////////////////////////////////////////////////////////

///////////////////////////////////////////////////////////////////////
///  This function converts decimal degrees to radians              ///
///////////////////////////////////////////////////////////////////////
func deg2rad(deg:Double) -> Double {
    return deg * M_PI / 180
}

///////////////////////////////////////////////////////////////////////
///  This function converts radians to decimal degrees              ///
///////////////////////////////////////////////////////////////////////
func rad2deg(rad:Double) -> Double {
    return rad * 180.0 / M_PI
}

func distance(lat1:Double, lon1:Double, lat2:Double, lon2:Double, unit:String) -> Double {
    let theta = lon1 - lon2
    var dist = sin(deg2rad(lat1)) * sin(deg2rad(lat2)) + cos(deg2rad(lat1)) * cos(deg2rad(lat2)) * cos(deg2rad(theta))
    dist = acos(dist)
    dist = rad2deg(dist)
    dist = dist * 60 * 1.1515
    if (unit == "K") {
        dist = dist * 1.609344
    }
    else if (unit == "N") {
        dist = dist * 0.8684
    }
    return dist
}

print(distance(Double(32.9697), lon1: Double(-96.80322), lat2: Double(29.46786), lon2: Double(-98.53506), unit: "M"), "Miles")
print(distance(Double(32.9697), lon1: Double(-96.80322), lat2: Double(29.46786), lon2: Double(-98.53506), unit: "K"), "Kilometers")
print(distance(Double(32.9697), lon1: Double(-96.80322), lat2: Double(29.46786), lon2: Double(-98.53506), unit: "N"), "Nautical Miles")