src/FirstClass.php
public function encodeString($string)
    {
        $string=strtolower($string);
        $src="abcdefghijklmnopqrstuvwxyz0123456789 ";
        $dst="jklmnopqrstuvwxyz0123456789abcdefghi ";
        for ($i=0; $i<strlen($string); $i++) {
            $pos=strpos($src, $string[$i]);
            if ($pos===false) {
                throw new \Exception("Please provide only numbers and alphanumerical characters");
            }
            $string[$i]=$dst[$pos];
        }
        return $string;
    }
public function encodeString($string)
    {
        $string=strtolower($string);
        $src="abcdefghijklmnopqrstuvwxyz0123456789 ";
        $dst="jklmnopqrstuvwxyz0123456789abcdefghi ";
        for ($i=0; $i<strlen($string); $i++) {
            $pos=strpos($src, $string[$i]);
            if ($pos===false) {
                throw new \Exception("Please provide only numbers and alphanumerical characters");
            }
            $string[$i]=$dst[$pos];
        }
        return $string;
    }
Encodes a string by a simple shift of characters

@param string $string
@return string
@throws \Exception