add.php

<?php
/** @var string $userName */
/** @var bool $isAuth */

require_once __DIR__ . '/init.php';

/** @var mysqli $dbConnection */
if (!$dbConnection) {
    exit('Не удалось подключиться к базе данных');
}

$categories = getCategories($dbConnection);

if (!$categories) {
    exit('Не удалось получить категории товаров');
}

$formData = [];
$fileData = [];
$errors = [];

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    // получаем данные
    $formData = $_POST;
    $fileData = $_FILES;
    $errors = validateFormAddLot($formData, $fileData);
    $file = uploadFile($fileData['lot-img']);

    if (empty($errors) && $file !== false) {
        $formData['lot-img'] = $file;
        $formData['author'] = 1;

        $id = addLot($dbConnection, $formData);
        header("Location: /lot.php?id=$id");
    }
}

$content = includeTemplate('add-lot.php',
    [
        'categories' => $categories,
        'formData' => $formData,
        'fileData' => $fileData,
        'errors' => $errors,
    ]
);

$layout = includeTemplate('layout.php',
    [
        'title' => 'Главная',
        'userName' => $userName,
        'isAuth' => $isAuth,
        'content' => $content,
        'categories' => $categories,
        'cssClass' => '',
    ]
);

print($layout);