<?php
/**
 * @package    Grav.Common.Helpers
 *
 * @copyright  Copyright (C) 2015 - 2018 Trilby Media, LLC. All rights reserved.
 * @license    MIT License; see LICENSE file for details.
 */

namespace Grav\Common\Helpers;

class Base32 {
    protected static $base32Chars =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
    protected static $base32Lookup = array(
        0xFF,0xFF,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F, // '0', '1', '2', '3', '4', '5', '6', '7'
        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF, // '8', '9', ':', ';', '<', '=', '>', '?'
        0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06, // '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G'
        0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E, // 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O'
        0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16, // 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W'
        0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF, // 'X', 'Y', 'Z', '[', '\', ']', '^', '_'
        0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06, // '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g'
        0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E, // 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o'
        0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16, // 'p', 'q', 'r', 's', 't', 'u', 'v', 'w'
        0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF  // 'x', 'y', 'z', '{', '|', '}', '~', 'DEL'
    );

    /**
     * Encode in Base32
     *
     * @param $bytes
     * @return string
     */
    public static function encode( $bytes ) {
        $i = 0; $index = 0; $digit = 0;
        $base32 = '';
        $bytes_len = strlen($bytes);
        while( $i < $bytes_len ) {
            $currByte = ord($bytes{$i});
            /* Is the current digit going to span a byte boundary? */
            if( $index > 3 ) {
                if( ($i + 1) < $bytes_len ) {
                    $nextByte = ord($bytes{$i+1});
                } else {
                    $nextByte = 0;
                }
                $digit = $currByte & (0xFF >> $index);
                $index = ($index + 5) % 8;
                $digit <<= $index;
                $digit |= $nextByte >> (8 - $index);
                $i++;
            } else {
                $digit = ($currByte >> (8 - ($index + 5))) & 0x1F;
                $index = ($index + 5) % 8;
                if( $index === 0 ) $i++;
            }
            $base32 .= self::$base32Chars{$digit};
        }
        return $base32;
    }

    /**
     * Decode in Base32
     *
     * @param $base32
     * @return string
     */
    public static function decode( $base32 ) {
        $bytes = array();
        $base32_len = strlen($base32);
        for( $i=$base32_len*5/8-1; $i>=0; --$i ) {
            $bytes[] = 0;
        }
        for( $i = 0, $index = 0, $offset = 0; $i < $base32_len; $i++ ) {
            $lookup = ord($base32{$i}) - ord('0');
            /* Skip chars outside the lookup table */
            if( $lookup < 0 || $lookup >= count(self::$base32Lookup) ) {
                continue;
            }
            $digit = self::$base32Lookup[$lookup];
            /* If this digit is not in the table, ignore it */
            if( $digit == 0xFF ) continue;
            if( $index <= 3 ) {
                $index = ($index + 5) % 8;
                if( $index == 0) {
                    $bytes[$offset] |= $digit;
                    $offset++;
                    if( $offset >= count($bytes) ) break;
                } else {
                    $bytes[$offset] |= $digit << (8 - $index);
                }
            } else {
                $index = ($index + 5) % 8;
                $bytes[$offset] |= ($digit >> $index);
                $offset++;
                if ($offset >= count($bytes) ) break;
                $bytes[$offset] |= $digit << (8 - $index);
            }
        }
        $bites = '';
        foreach( $bytes as $byte ) $bites .= chr($byte);
        return $bites;
    }
}
