index/src/Serialisation/Base62.php

<?php
// Base62.php
// Created: 2022-01-28
// Updated: 2023-07-21

namespace Index\Serialisation;

use Index\IO\Stream;

/**
 * Provides a Base62 serialiser.
 */
final class Base62 {
    private const CHARS = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

    /**
     * Encodes an integer as a Base62 string.
     *
     * @param int $input Integer.
     * @return string Base64 string representing the integer.
     */
    public static function encode(int $input): string {
        $output = '';

        for($i = floor(log10($input) / log10(62)); $i >= 0; --$i) {
            $index = (int)floor($input / (62 ** $i));
            $output .= substr(self::CHARS, $index, 1);
            $input -= $index * (62 ** $i);
        }

        return $output;
    }

    /**
     * Decodes a Base62 string back to an integer.
     *
     * @param Stream|string $input Input Base62 string.
     * @return int Integer.
     */
    public static function decode(Stream|string $input): int {
        $input = (string)$input;
        $output = 0;
        $length = strlen($input) - 1;

        for($i = 0; $i <= $length; ++$i)
            $output += strpos(self::CHARS, $input[$i]) * (62 ** ($length - $i));

        return $output;
    }
}