Dynamically set post featured image to existent posts

gistfile1.txt

<?php
/*
 * This script will process all images from the specified directory from your server and set them as featured images
 * for posts.
 *
 * 1) Upload all images to wp-content/uploads/DIR_NAME  -- Only images should be in that directory!
 * 2) Update BHWP_UPLOADS_DIR to match the name of your directory
 */

/*
 * Holds the full system path to the images directory
 * Replace DIR_NAME with your directory name
 */
define('BHWP_UPLOADS_DIR', ABSPATH.'wp-content/uploads/DIR_NAME');



/**
 * Retrieve all images from the directory
 * @return array
 */
function bhwp_getLocalFiles(){
    return glob(BHWP_UPLOADS_DIR.'/*');
}

/**
 * Set the featured image to the specified post
 * @param string     $localFilePath The system path to the image
 * @param int        $postID The post ID
 * @param bool|false $force Whether or not to replace the existent featured image if the post has one
 */
function bhwp_setPostThumbnail( $localFilePath, $postID, $force = false )
{
    if(! $force && has_post_thumbnail($postID)){
        return;
    }

    // The ID of the post this attachment is for.
    $parent_post_id = $postID;

    // Check the type of file. We'll use this as the 'post_mime_type'.
    $filetype = wp_check_filetype( basename( $localFilePath ), null );

    // Get the path to the upload directory.
    $wp_upload_dir = wp_upload_dir();

    // Prepare an array of post data for the attachment.
    $attachment = array(
        'guid'           => $wp_upload_dir['url'] . '/' . basename( $localFilePath ),
        'post_mime_type' => $filetype['type'],
        'post_title'     => preg_replace( '/\.[^.]+$/', '', basename( $localFilePath ) ),
        'post_content'   => '',
        'post_status'    => 'inherit'
    );

    // Insert the attachment.
    $attach_id = wp_insert_attachment( $attachment, $localFilePath, $parent_post_id );

    // Make sure that this file is included, as wp_generate_attachment_metadata() depends on it.
    require_once( ABSPATH . 'wp-admin/includes/image.php' );

    // Generate the metadata for the attachment, and update the database record.
    $attach_data = wp_generate_attachment_metadata( $attach_id, $localFilePath );
    wp_update_attachment_metadata( $attach_id, $attach_data );

    // Set post's featured image
    set_post_thumbnail($postID, $attach_id);
}

/*
 * Get all posts
 */
$posts = get_posts(array(
    'post_type'   => 'post',
    'numberposts' => -1, // Loop through all posts
));
/*
 * Loop through all posts and set a featured image to each of them
 */
if($posts){
    $images = bhwp_getLocalFiles();
    $ix = 0;
    $numImages = count($images);
    foreach($posts as $post)
    {
        setup_postdata($post);
        if($ix >= $numImages){
            $ix = 0;
        }
        $imagePath = $images[$ix];
        bhwp_setPostThumbnail($imagePath, $post->ID);
        $ix++;
    }
    wp_reset_postdata();
    echo 'Done';
}
else { echo 'no posts found';}