Grab and Insert Image to a post in wordpress

if (isset($IMG_URL) {
    $upload_dir = wp_upload_dir();
    $image_data = file_get_contents($IMG_URL);
    $filename = basename($IMG_URL);
    if(wp_mkdir_p($upload_dir['path']))
        $file = $upload_dir['path'] . '/' . $filename;
    else
        $file = $upload_dir['basedir'] . '/' . $filename;
    file_put_contents($file, $image_data);

    $wp_filetype = wp_check_filetype($filename, null );
    $attachment = array(
        'post_mime_type' => $wp_filetype['type'],
        'post_title' => sanitize_file_name($filename),
        'post_content' => '',
        'post_status' => 'inherit'
    );
    $attach_id = wp_insert_attachment( $attachment, $file, $post_id );
    require_once(ABSPATH . 'wp-admin/includes/image.php');
    $attach_data = wp_generate_attachment_metadata( $attach_id, $file );
    wp_update_attachment_metadata( $attach_id, $attach_data );

    set_post_thumbnail( $post_id, $attach_id );
}