String Nth-position Laravel

MacroProvider.php

Str::macro('nth_position',function($str, $letter, $n, $offset = 0){
            $str_arr = str_split($str);
            $letter_size = array_count_values(str_split(substr($str, $offset)));
            if( !isset($letter_size[$letter])){
                return false;
            } else if($letter_size[$letter] < $n) {
                return false;
            }
            for($i = $offset, $x = 0, $count = (count($str_arr) - $offset); $i < $count, $x != $n; $i++){
                if($str_arr[$i] == $letter){
                    $x++;
                }
            }
            return $i - 1;
        });