class Base64Encoder

class Base64Encoder implements EncoderInterface {
    
    /**
     * Takes an unencoded string and produces a Base64 encoded string from it.
     *
     * Base64 encoded strings have a maximum line length of 76 characters.
     * If the first line needs to be shorter, indicate the difference with
     * $firstLineOffset.
     */
    public function encodeString(string $string, ?string $charset = 'utf-8', int $firstLineOffset = 0, int $maxLineLength = 0) : string {
        if (0 >= $maxLineLength || 76 < $maxLineLength) {
            $maxLineLength = 76;
        }
        $encodedString = base64_encode($string);
        $firstLine = '';
        if (0 !== $firstLineOffset) {
            $firstLine = substr($encodedString, 0, $maxLineLength - $firstLineOffset) . "\r\n";
            $encodedString = substr($encodedString, $maxLineLength - $firstLineOffset);
        }
        return $firstLine . trim(chunk_split($encodedString, $maxLineLength, "\r\n"));
    }

}