functions.php

<?php

function getGenres($sql) {
    return $sql->query("SELECT * FROM genres ORDER BY name")->fetchAll();
}

function getBooks($sql) {
    return $sql->query("
        SELECT books.*, genres.name AS genre
        FROM books
        JOIN genres ON books.genre_id = genres.id
        ORDER BY books.id DESC
    ")->fetchAll();
}

function searchBooks($sql, $search, $genre_id) {
    $stmt = $sql->prepare("
        SELECT books.*, genres.name AS genre
        FROM books
        JOIN genres ON books.genre_id = genres.id
        WHERE (books.title LIKE ? OR books.author LIKE ?)
        AND (? = '' OR books.genre_id = ?)
        ORDER BY books.id DESC
    ");

    $stmt->execute([
        "%" . $search . "%",
        "%" . $search . "%",
        $genre_id,
        $genre_id
    ]);

    return $stmt->fetchAll();
}

?>