<?php
# Original source: https://github.com/bbars/utils/tree/master/php-base32-encode-decode

namespace lfkeitel\phptotp;

class Base32
{
    const BITS_5_RIGHT = 31;
    protected static $CHARS = 'abcdefghijklmnopqrstuvwxyz234567';

    public static function encode($data)
    {
        $dataSize = strlen($data);
        $res = '';
        $remainder = 0;
        $remainderSize = 0;

        for ($i = 0; $i < $dataSize; $i++) {
            $b = ord($data[$i]);
            $remainder = ($remainder << 8) | $b;
            $remainderSize += 8;
            while ($remainderSize > 4) {
                $remainderSize -= 5;
                $c = $remainder & (self::BITS_5_RIGHT << $remainderSize);
                $c >>= $remainderSize;
                $res .= self::$CHARS[$c];
            }
        }
        if ($remainderSize > 0) {
            // remainderSize < 5:
            $remainder <<= (5 - $remainderSize);
            $c = $remainder & self::BITS_5_RIGHT;
            $res .= self::$CHARS[$c];
        }

        return $res;
    }

    public static function decode($data)
    {
        $data = strtolower($data);
        $dataSize = strlen($data);
        $buf = 0;
        $bufSize = 0;
        $res = '';

        for ($i = 0; $i < $dataSize; $i++) {
            $c = $data[$i];
            $b = strpos(self::$CHARS, $c);
            if ($b === false) {
                throw new \Exception('Encoded string is invalid, it contains unknown char #'.ord($c));
            }
            $buf = ($buf << 5) | $b;
            $bufSize += 5;
            if ($bufSize > 7) {
                $bufSize -= 8;
                $b = ($buf & (0xff << $bufSize)) >> $bufSize;
                $res .= chr($b);
            }
        }

        return $res;
    }
}