<?php

class distance
{
    public function meters($lat1, $lng1, $lat2, $lng2) {
        // Radius of the Earth in meters :
        $earth_radius = 6378137;
        // Calculation of the distance between 2 GPS coordinates:
        $rlo1 = deg2rad($lng1);
        $rla1 = deg2rad($lat1);
        $rlo2 = deg2rad($lng2);
        $rla2 = deg2rad($lat2);
        $dlo = ($rlo2 - $rlo1) / 2;
        $dla = ($rla2 - $rla1) / 2;
        $a = (sin($dla) * sin($dla)) + cos($rla1) * cos($rla2) * (sin($dlo) * sin($dlo));
        $d = 2 * atan2(sqrt($a), sqrt(1 - $a));
        // Return the distance in meters between 2 GPS points
        return round($earth_radius * $d);
    }
}

class ListUser
{
    public function ListOfUser() {
        $listUser = ["001","002","003"];
        // Actual coordinates of User in $lat1 and $lng1
        $lat1 = 45.891773;
        $lng1 = 4.662613;
        //traverse of all the coordinates stored in the PHP server
        $userID = "004";
        $dist =  (new distance)->meters($lat1,$lng1,45.777222,3.087025);
        if ($dist <= 100 ){
            $listUser[] = $userID;
        }
        return $listUser;
    }
}


echo "Normalement pas bcp = ";
echo (new distance)->meters(45.762595,3.108837,45.762524,3.1088743);
/*
echo "Normalement pas beaucoup = ";
echo (new distance)->distentre2co(45.891773, 4.662613,45.777222,3.087025);
*/
echo "\nListe User = ";
echo implode(",",(new ListUser)->ListOfUser());