Batch Set External Images in Content as Featured Images

plugin.php

<?php
/**
 * Batch Set External Images in Content as Featured Images
 *
 * Look for external images shoved into the content, upload them to the Media Library, and assign it as the featured post.
 *
 * @package   batch_upload_featured
 * @author    Cliff Seal <cliff@evermo.re>
 * @link      http://evermo.re
 * @copyright 2015 Logos Creative
 *
 * @wordpress-plugin
 * Plugin Name: Batch Set External Images in Content as Featured Images
 * Plugin URI:   http://evermo.re
 * Description: Look for external images shoved into the content, upload them to the Media Library, and assign it as the featured post.
 * Version:     1.0.0
 * Author:      Evermore <cliff@evermo.re>
 * Author URI:  http://evermo.re
 */

// If this file is called directly, abort.
if ( ! defined( 'WPINC' ) ) {
	die;
}

/**
 * Plugin class.
 *
 * @package batch_upload_featured
 * @author  Cliff Seal <cliff@evermo.re>
 */
class batch_upload_featured {

	/**
	 * Plugin version, used for cache-busting of style and script file references.
	 *
	 * @since   1.0.0
	 *
	 * @const   string
	 */
	const VERSION = '1.0.0';

	/**
	 * Instance of this class.
	 *
	 * @since    1.0.0
	 *
	 * @var      object
	 */
	protected static $instance = null;

	/**
	 * Initialize the plugin by setting localization, filters, and administration functions.
	 *
	 * @since     1.0.0
	 */
	private function __construct() {

		add_action( 'wp_footer', array( $this, 'batch_upload_featured_batch_media_migrate' ), 35);

		add_action( 'wp_ajax_batch_upload_featured_do_migration_media', array( $this, 'batch_upload_featured_do_migration_media' ) );

	}

	/**
	 * Return an instance of this class.
	 *
	 * @since     1.0.0
	 *
	 * @return    object    A single instance of this class.
	 */
	public static function get_instance() {

		// If the single instance hasn't been set, set it now.
		if ( null == self::$instance ) {
			self::$instance = new self;
		}

		return self::$instance;
	}

	/**
	 * Add the Javascript call to the footer
	 *
	 * @since     1.0.0
	 *
	 * @return    object    An instance of the form
	 */

	public function batch_upload_featured_batch_media_migrate() {
		if ( isset($_GET['batchthumbnail']) && $_GET['batchthumbnail'] === 'run' ) {
			?>
			<script>

				jQuery(document).ready(function () {
					batch_upload_featured_migration_media();
				});
				function batch_upload_featured_migration_media() {
					return jQuery.ajax({
						url: "<?php echo admin_url( 'admin-ajax.php' ); ?>",
						data: {
							action: 'batch_upload_featured_do_migration_media',
							time: '<?php echo time(); ?>'
						},
						success: function (response) {
							batch_upload_featured_migration_media();
							console.log(response);
						},
						failure: function (response) {
							console.log('fail?');
							console.log(response);
						},
						cache: false

					});
				}

			</script>
		<?php
		}
	}

	public function batch_upload_featured_do_migration_media() {

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

		$offset = (int) get_option( 'batch_upload_featured_media_offset_counter', 0 );
		if ( !$offset ) {
			$offset = 0;
		}
		$count_posts = wp_count_posts();
		$highest = $count_posts->publish;

		if( $offset > $highest ) {
			echo 'VICTORY!' . $offset . ' ' . $highest;
			status_header( 404 );
			die();
		}

		$args = array(
			'posts_per_page' => 5,
			'offset' => $offset
		);

		$allposts = get_posts($args);

		foreach ( $allposts as $thispost ) {

			if ( !has_post_thumbnail($thispost->ID) ) {

				preg_match_all( '/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $thispost->post_content, $thispostsimages );

				if ( $thispostsimages[1] ) {

					foreach ( $thispostsimages[1] as $oneimagetag ) {

						$fullsizeimage = preg_replace('/-[0-9]{1,4}x[0-9]{1,4}/i', '', $oneimagetag);

						if ( file_exists($fullsizeimage) ) {

							$oneimagetag = $fullsizeimage;

						}

						$image = media_sideload_image($oneimagetag, $thispost->ID);

						if ( !is_wp_error($image) ) {

							$attachedimages = get_attached_media( 'image', $thispost->ID );

							if ( $attachedimages ) {

								$i = 0;

								foreach ( $attachedimages as $attachedimage ) {

									if ( $i === 0 ) {

										$postthumbnail = set_post_thumbnail( $thispost->ID, $attachedimage->ID );

										if ( $postthumbnail ) {

											echo 'Changed post thumbnail on post ' . $postthumbnail . '. ';

										} else {

											echo 'Did not change post thumbnail on post ' . $thispost->ID . '. ';

										}

									}

									$i++;

								}

							}

						}

					}

				}

			}

			$offset++;

		}

		update_option( 'batch_upload_featured_media_offset_counter', $offset );
		status_header( 200 );
		die();

	}

}

batch_upload_featured::get_instance();