index/src/Serialisation/Base32.php

<?php
// Base32.php
// Created: 2022-01-13
// Updated: 2024-07-31

namespace Index\Serialisation;

/**
 * Provides Base32 encoding.
 */
final class Base32 {
    private const CHARS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';

    /**
     * Encodes data with RFC4648 base32.
     *
     * @param string $string The data to encode.
     * @return string The encoded data, as a string.
     */
    public static function encode(string $string): string {
        $length = strlen($string);
        $bin = '';
        $output = '';

        for($i = 0; $i < $length; $i++)
            $bin .= sprintf('%08b', ord($string[$i]));

        $bin = str_split($bin, 5);
        $last = array_pop($bin);
        $bin[] = str_pad((string)$last, 5, '0', STR_PAD_RIGHT);

        foreach($bin as $part)
            $output .= self::CHARS[bindec($part)];

        return $output;
    }

    /**
     * Decodes data encoded with RFC4648 base32.
     *
     * @param string $string The encoded data.
     * @return string|false Returns the decoded data or false on failure. The returned data may be binary.
     */
    public static function decode(string $string): string|false {
        $length = strlen($string);
        $char = $shift = 0;
        $output = '';

        for($i = 0; $i < $length; $i++) {
            $pos = stripos(self::CHARS, $string[$i]);
            if($pos === false)
                return false;

            $char <<= 5;
            $char += $pos;
            $shift = ($shift + 5) % 8;
            $output .= $shift < 5 ? chr(($char & (0xFF << $shift)) >> $shift) : '';
        }

        return $output;
    }
}