Ajuda para colocar imagem upada como destaque em post na criação de plugin

Estou construindo um plugin e está dando tudo certo, consegui bons resultados na postagem de videos e com o codigo, consigo fazer o upload de uma imagem atraves de uma url, no entaanto não estou conseguindo ligar a imagem upada ao post que é criado com o envio do formulário. Gostaria muito que me ajudassem. Obrigado.

Segue o código do plugin.

<h1>Vídeos ---ôs PRO</h1>
<!-- New Post Form -->

<div id="postbox">
<form id="new_post" name="new_post" method="post" action="">
<label for="title">Titulo do video</label>
<input type="text" id="title" value="" tabindex="1" size="40" name="title" />

<label for="description">Descrição do Video</label>
<textarea id="description" tabindex="3" name="description" cols="50" rows="6"></textarea>

<label for="site">Site</label>
<select id="site" name="site" size="1">
<option selected="selected">Selecione o site</option>
<option value="xvideos">xvideos</option>
<option value="redtube">redtube</option>
<option value="xhamster">xhamster</option>
<option value="---hub">---hub</option>
<option value="---ocarioca">---ocarioca</option>
<option value="you---">you---</option>
<option value="tube8">tube8</option>
<option value="xtube">xtube</option>
</select>

<label for="categoria">Categoria da postagem</label>
<?php wp_dropdown_categories( 'show_option_none=Slecione a categoria&tab_index=4&taxonomy=category' ); ?>

<label for="url">URL do video</label>
<input type="text" id="url" value="" tabindex="1" size="40" name="url" />

<label for="post_tags">Tags</label>
<input type="text" value="" tabindex="5" size="16" name="post_tags" id="post_tags" />

<label for="url">Status do Video</label>
<input id="status" name="status" type="radio" value="draft" checked="checked">Deixar como Rascunho &nbsp;&nbsp;
<input id="status" name="status" type="radio" value="publish"> Publicar Agora

<br>
<p align="left"><input type="submit" value="Enviar" tabindex="6" id="submit" name="submit" size="10" />

<input type="hidden" name="post_type" id="post_type" value="post" />
<input type="hidden" name="action" value="post" />
<?php wp_nonce_field( 'new-post' ); ?>
</form>
</div>

<!--// New Post Form -->

<?php
if( 'POST' == $_SERVER['REQUEST_METHOD'] && !empty( $_POST['action'] )) {

 // Do some minor form validation to make sure there is content
 if (isset ($_POST['title'])) {
 $title = $_POST['title'];
 } else {
 echo 'Por favor preencha o título!';
 }
 if (isset ($_POST['description'])) {

 $description = $_POST['description'];

 } else {
 echo 'Please enter the content';
 }
 if (isset ($_POST['site'])) {
 $site = $_POST['site'];

 if (isset ($_POST['cat'])) {
 $cat = $_POST['cat'];
 } else {
 echo 'Por favor selecione a categoria!';
 }
 if (isset ($_POST['url'])) {

 //inicio condição
 if ( $site == "xvideos" ) {
 $src = $_POST['url'];
 $video = substr(@parse_url($src, PHP_URL_PATH), 6);
 $video_id = strtok($video, '/');

//inicio da captura e envio da imagemao servidor

$endereco = file_get_contents($src);
$pegar = preg_match_all('/<meta property="og:image" content=(.+)\/>/', $endereco, $conteudo);

$image_s1 = $conteudo[1][0]; // Define the image URL here

$image_s2 = substr($image_s1, 1);
$image_s3 = strtok($image_s2, '"');
$image_url = $image_s3;
$image_name = $video_id.'.jpg';

$upload_dir = wp_upload_dir(); // Set upload folder
$image_data = file_get_contents($image_url); // Get image data
$unique_file_name = wp_unique_filename( $upload_dir['path'], $image_name ); // Generate unique name
$filename = basename( $unique_file_name ); // Create image file name
$file_path = get_site_url() . '/wp-content/uploads/' . $image_name; // Get the futur file path of the image
if( !file_exists($file_path) ){ // Check if image is already in upload_dir
// Check folder permission and define file location
if( wp_mkdir_p( $upload_dir['path'] ) ) {
$file = $upload_dir['path'] . '/' . $filename;
} else {

$file = $upload_dir['basedir'] . '/' . $filename;
}

// Create the image file on the server
file_put_contents( $file, $image_data );
// Check image file type
$wp_filetype = wp_check_filetype( $filename, null );
// Set attachment data
$attachment = array(
'post_mime_type' => $wp_filetype['type'],
'post_title' => sanitize_file_name( $filename ),
'post_content' => '',
'post_status' => 'inherit'
);
// Create the attachment
$attach_id = wp_insert_attachment( $attachment, $file, $post_id );
// Include image.php

require_once(ABSPATH . 'wp-admin/includes/media.php');
require_once(ABSPATH . 'wp-admin/includes/file.php');
require_once(ABSPATH . 'wp-admin/includes/image.php');

// Define attachment metadata
$attach_data = wp_generate_attachment_metadata( $attach_id, $file );
// Assign metadata to attachment
wp_update_attachment_metadata( $attach_id, $attach_data );
// And finally assign featured image to post

set_post_thumbnail( $post_id, $attach_id );
}

 }
 elseif ( $site == "redtube" ) {
 $src = $_POST['url'];
 $video_id = (int) substr(@parse_url($src, PHP_URL_PATH), 1);

 }
 elseif ( $site == "xhamster" ) {
 $src = $_POST['url'];
 $video = substr(@parse_url($src, PHP_URL_PATH), 8);
 $video_id = strtok($video, '/');
 }
 elseif ( $site == "---hub" ) {
 $src = $_POST['url'];
 $posicao = strpos($src, '=');
 $video_id = substr($src, $posicao+1);
 }
 elseif ( $site == "---ocarioca" ) {
 $src = $_POST['url'];
 $posicao = strpos($src, 'video/');
 $video = substr($src, $posicao+6);
 $video_id = strtok($video, '"');
 }
 elseif ( $site == "your---" ) {
 $src = $_POST['url'];
 $video = substr(@parse_url($src, PHP_URL_PATH), 7);
 $video_id = strtok($video, '/');
 }
 elseif ( $site == "tube8" ) {
 $src = $_POST['url'];
 $video_id = substr(@parse_url($src, PHP_URL_PATH), 1);
 }
 elseif ( $site == "xtube" ) {
 $src = $_POST['url'];
 $video_id = substr(@parse_url($src, PHP_URL_PATH), 13);
 }
 //fim condição

 //$src = $_POST['url'];
 //$video = substr(@parse_url($src, PHP_URL_PATH), 6);
 //$video_id = strtok($video, '/');

 } else {
 echo 'Por favor preencha o endereço do video!';
 }
 }
 $tags = $_POST['post_tags'];
 if (isset ($_POST['status'])) {
 $status = $_POST['status'];
 } else {
 echo 'Por favor selecione a categoria!';
 }

 // Add the content of the form to $post as an array
 $post = array(
 'post_title'	=> $title,
 'post_content'	=> ''.$description.'[videoin site='.$site.' width=660 height=460 id='.$video_id.'][/videoin]
<br><br>O melhor conteúdo ---ô você encontra aqui. As melhores fotos e os videos mais picantes. Atualizações diárias!',
 'post_category'	=> array($_POST['cat']), // Usable for custom taxonomies too
 'tags_input'	=> $tags,
 'post_status'	=> $status, // Choose: publish, preview, future, etc.
 'post_type'	=> $_POST['post_type'] // Use a custom post type if you want to
 );

 wp_insert_post($post); // Pass the value of $post to WordPress the insert function
 // http://codex.wordpress.org/Function_Reference/wp_insert_post
 wp_redirect( home_url() );

} // end IF

// Do the wp_insert_post action to insert it

do_action('wp_insert_post', 'wp_insert_post');

?>