tako zone redirect script (it sucks)

_base62.php

<?php
define('BASE62_CHARS', '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');

function base62_encode(int $input): string {
    $output = '';

    for($i = floor(log10($input) / log10(62)); $i >= 0; --$i) {
        $index = (int)floor($input / (62 ** $i));
        $output .= substr(BASE62_CHARS, $index, 1);
        $input -= $index * (62 ** $i);
    }

    return $output;
}

function base62_decode(string $input): int {
    $output = 0;
    $length = strlen($input) - 1;

    for($i = 0; $i <= $length; ++$i)
        $output += strpos(BASE62_CHARS, $input[$i]) * (62 ** ($length - $i));

    return $output;
}

// whoa is this pytohn !!?
if(basename($_SERVER['PHP_SELF']) === basename(__FILE__)) {
    if(!empty($_GET['decode']) && is_string($_GET['decode']))
        echo base62_decode($_GET['decode']);
    elseif(!empty($_GET['encode']) && is_string($_GET['encode']))
        echo base62_encode($_GET['encode']);
}

go.php

<?php
require_once '_base62.php';

try {
    $pdo = new PDO('mysql:unix_socket=/var/run/mysqld/mysqld.sock;dbname=takozone;charset=utf8mb4', 'takozone', 'secret~', [
        PDO::ATTR_CASE => PDO::CASE_NATURAL,
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_ORACLE_NULLS => PDO::NULL_NATURAL,
        PDO::ATTR_STRINGIFY_FETCHES => false,
        PDO::ATTR_EMULATE_PREPARES => false,
        PDO::MYSQL_ATTR_INIT_COMMAND => "
            SET SESSION
                sql_mode = 'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION',
                time_zone = '+00:00';
        ",
    ]);
} catch(Exception $ex) {
    echo '<h3>Unable to connect to database</h3>';
    die($ex->getMessage());
}

$horrendous = substr($_SERVER['HTTP_USER_AGENT'], 0, 7) === 'Satori/';

if(!empty($_GET['create']) && is_string($_GET['create']) && ($horrendous || in_array($_SERVER['REMOTE_ADDR'], ['188.166.77.99', '2a03:b0c0:2:d0::d62:2001']))) {
    /*$getExisting = $pdo->prepare('
        SELECT `link_id` FROM `tako_links` WHERE `link_target` = :target
    ');
    $getExisting->bindValue('target', $_GET['create']);
    $linkId = $getExisting->execute() ? (int)$getExisting->fetchColumn() : 0;

    if($linkId < 1) {
        $insertLink = $pdo->prepare('
            INSERT INTO `tako_links` (`link_target`)
            VALUES (:target)
        ');
        $insertLink->bindValue('target', $_GET['create']);
        $insertLink->execute();
        $linkId = (int)$pdo->lastInsertId();
    }
    
    echo 'https://tako.zone/g/' . base62_encode($linkId);*/
    exit;
}

$linkId = filter_input(INPUT_GET, 'id');
$linkId = base62_decode($linkId);

if($linkId > 0) {
    $getLink = $pdo->prepare('
        SELECT `link_target`
        FROM `tako_links`
        WHERE `link_id` = :id
    ');
    $getLink->bindValue('id', $linkId);
    $linkTarget = $getLink->execute() ? $getLink->fetchColumn() : '';
}

if(empty($linkTarget))
    $linkTarget = '/';

header("Location: $linkTarget");