[PHP] Databaseless User Online Counter

<?php
$timeout = 2;
$time = time();
$ip = $_SERVER["REMOTE_ADDR"];
$file = "users.txt";
$arr = file($file);
$users = 0;

for ($i = 0; $i < count($arr); $i++){
    if ($time - intval(substr($arr[$i], strpos($arr[$i], "    ") + 4)) > $timeout){
        unset($arr[$i]);
        $arr = array_values($arr);
        file_put_contents($file, implode($arr));
    }
    $users++;
}

//if($_GET["sts"] === "")
echo $users;

for ($i = 1; $i < count($arr); $i++){
    if (substr($arr[$i], 0, strlen($ip)) == $ip){
        $arr[$i] = substr($arr[$i], 0, strlen($ip))."    ".$time."\n";
        $arr = array_values($arr);
        file_put_contents($file, implode($arr));
        exit;
    }
}

file_put_contents($file, $ip."    ".$time."\n", FILE_APPEND);
?>