index/src/Serialisation/Base32.php

<?php
// Base32.php
// Created: 2022-01-13
// Updated: 2023-07-21

namespace Index\Serialisation;

use Index\IO\Stream;

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

    /**
     * Encodes binary data as a Base32 string.
     *
     * @param Stream|string $input Input binary data.
     * @return string Base32 string representing the binary data.
     */
    public static function encode(Stream|string $input): string {
        $input = (string)$input;
        $length = strlen($input);
        $bin = '';
        $output = '';

        for($i = 0; $i < $length; $i++)
            $bin .= sprintf('%08b', ord($input[$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 a Base32 string back to binary data.
     *
     * @param Stream|string $input Input Base32 string.
     * @return string Binary data.
     */
    public static function decode(Stream|string $input): string {
        $input = (string)$input;
        $length = strlen($input);
        $char = $shift = 0;
        $output = '';

        for($i = 0; $i < $length; $i++) {
            $char <<= 5;
            $char += stripos(self::CHARS, $input[$i]);
            $shift = ($shift + 5) % 8;
            $output .= $shift < 5 ? chr(($char & (0xFF << $shift)) >> $shift) : '';
        }

        return $output;
    }
}