Clicking "View details" leads to catalog.php

<?php 

include("inc/data.php");
include("inc/functions.php");




if (isset($_GET["is"])) {
    $id = $_GET["id"];
    if (isset($catalog[$id])) {
        $item = $catalog[$id];
    }
} 

if (!isset($item)) {
    header("location:catalog.php");
    exit;
}


$pageTitle = $item['title'];
$section = null;
include ("inc/header.php"); ?>

<div calss="section page">
    <div class="wrapper">
        <div class="media-picture">
            <span>
<img src="<?php echo $item["img"]; ?>" alt="<?php echo $item["title"]; ?>"/>
</span>
</div>
<div class="meadia-details"></div>
<h1><?php echo $item["title"]; ?></h1>
<table>
    <tr>
        <th>Category</th>
        <td><?php echo $item["category"]; ?></td>
    </tr>
    <tr>
        <th>Genre</th>
        <td><?php echo $item["genre"]; ?></td>
    </tr>
    <tr>
        <th>Format</th>
        <td><?php echo $item["format"]; ?></td>
    </tr>
    <tr>
        <th>Year</th>
        <td><?php echo $item["year"]; ?></td>
    </tr>
    <?php 
    if (strtolower($item["category"]) == "books") {
        ?>
    <tr>
        <th>Category</th>
        <td><?php echo $item["authors"]; ?></td>
    </tr>
    <tr>
        <th>Category</th>
        <td><?php echo $item["publisher"]; ?></td>
    </tr>
    <tr>
        <th>Category</th>
        <td><?php echo $item["isbn"]; ?></td>
    </tr>
    <?php }
    ?>
</table>


    </div>
</div>

<?php 

include("inc/data.php");
include("inc/functions.php");

$pageTitle = "Catalog";
$section = null;



if (isset($_GET["cat"])) {
if ($_GET["cat"] == "books") {
    $pageTitle = "Books";
    $section = "books";
} else if ($_GET["cat"] == "movies") {
    $pageTitle = "Movies";
    $section = "movies";
} else if ($_GET["cat"] == "music") {
    $pageTitle = "Music";
    $section = "music";
}
} 
include ("inc/header.php"); ?>

<div class="section catalog page">
    <div class ="wrapper">

    <h1><?php 
    if ($section != null) {
        echo "<a href='catalog.php'>Full Catalog</a> &gt; ";
    }
    echo $pageTitle; ?></h1>

    <ul class="items">
        <?php 
        $categories = array_category($catalog,$section);
                        foreach ($categories as $id) {
                        echo get_item_html($id,$catalog[$id]);
        }
        ?>
    </ul>


    </div>
</div>
<?php include ("inc/footer.php"); ?>