version.
			 * @param string $useragent           The useragent.
			 * @param string $pingback_server_url The server URL being linked to.
			 * @param string $pagelinkedto        URL of page linked to.
			 * @param string $pagelinkedfrom      URL of page linked from.
			 */
			$client->useragent = apply_filters( 'pingback_useragent', $client->useragent . ' -- WordPress/' . get_bloginfo( 'version' ), $client->useragent, $pingback_server_url, $pagelinkedto, $pagelinkedfrom );
			// When set to true, this outputs debug messages by itself.
			$client->debug = false;

			if ( $client->query( 'pingback.ping', $pagelinkedfrom, $pagelinkedto ) || ( isset( $client->error->code ) && 48 == $client->error->code ) ) { // Already registered.
				add_ping( $post, $pagelinkedto );
			}
		}
	}
}

/**
 * Checks whether blog is public before returning sites.
 *
 * @since 2.1.0
 *
 * @param mixed $sites Will return if blog is public, will not return if not public.
 * @return mixed Empty string if blog is not public, returns $sites, if site is public.
 */
function privacy_ping_filter( $sites ) {
	if ( '0' != get_option( 'blog_public' ) ) {
		return $sites;
	} else {
		return '';
	}
}

/**
 * Sends a Trackback.
 *
 * Updates database when sending trackback to prevent duplicates.
 *
 * @since 0.71
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $trackback_url URL to send trackbacks.
 * @param string $title         Title of post.
 * @param string $excerpt       Excerpt of post.
 * @param int    $ID            Post ID.
 * @return int|false|void Database query from update.
 */
function trackback( $trackback_url, $title, $excerpt, $ID ) {
	global $wpdb;

	if ( empty( $trackback_url ) ) {
		return;
	}

	$options            = array();
	$options['timeout'] = 10;
	$options['body']    = array(
		'title'     => $title,
		'url'       => get_permalink( $ID ),
		'blog_name' => get_option( 'blogname' ),
		'excerpt'   => $excerpt,
	);

	$response = wp_safe_remote_post( $trackback_url, $options );

	if ( is_wp_error( $response ) ) {
		return;
	}

	$wpdb->query( $wpdb->prepare( "UPDATE $wpdb->posts SET pinged = CONCAT(pinged, '\n', %s) WHERE ID = %d", $trackback_url, $ID ) );
	return $wpdb->query( $wpdb->prepare( "UPDATE $wpdb->posts SET to_ping = TRIM(REPLACE(to_ping, %s, '')) WHERE ID = %d", $trackback_url, $ID ) );
}

/**
 * Sends a pingback.
 *
 * @since 1.2.0
 *
 * @param string $server Host of blog to connect to.
 * @param string $path Path to send the ping.
 */
function weblog_ping( $server = '', $path = '' ) {
	require_once ABSPATH . WPINC . '/class-IXR.php';
	require_once ABSPATH . WPINC . '/class-wp-http-ixr-client.php';

	// Using a timeout of 3 seconds should be enough to cover slow servers.
	$client             = new WP_HTTP_IXR_Client( $server, ( ( ! strlen( trim( $path ) ) || ( '/' === $path ) ) ? false : $path ) );
	$client->timeout    = 3;
	$client->useragent .= ' -- WordPress/' . get_bloginfo( 'version' );

	// When set to true, this outputs debug messages by itself.
	$client->debug = false;
	$home          = trailingslashit( home_url() );
	if ( ! $client->query( 'weblogUpdates.extendedPing', get_option( 'blogname' ), $home, get_bloginfo( 'rss2_url' ) ) ) { // Then try a normal ping.
		$client->query( 'weblogUpdates.ping', get_option( 'blogname' ), $home );
	}
}

/**
 * Default filter attached to pingback_ping_source_uri to validate the pingback's Source URI.
 *
 * @since 3.5.1
 *
 * @see wp_http_validate_url()
 *
 * @param string $source_uri
 * @return string
 */
function pingback_ping_source_uri( $source_uri ) {
	return (string) wp_http_validate_url( $source_uri );
}

/**
 * Default filter attached to xmlrpc_pingback_error.
 *
 * Returns a generic pingback error code unless the error code is 48,
 * which reports that the pingback is already registered.
 *
 * @since 3.5.1
 *
 * @link https://www.hixie.ch/specs/pingback/pingback#TOC3
 *
 * @param IXR_Error $ixr_error
 * @return IXR_Error
 */
function xmlrpc_pingback_error( $ixr_error ) {
	if ( 48 === $ixr_error->code ) {
		return $ixr_error;
	}
	return new IXR_Error( 0, '' );
}

//
// Cache.
//

/**
 * Removes a comment from the object cache.
 *
 * @since 2.3.0
 *
 * @param int|array $ids Comment ID or an array of comment IDs to remove from cache.
 */
function clean_comment_cache( $ids ) {
	$comment_ids = (array) $ids;
	wp_cache_delete_multiple( $comment_ids, 'comment' );
	foreach ( $comment_ids as $id ) {
		/**
		 * Fires immediately after a comment has been removed from the object cache.
		 *
		 * @since 4.5.0
		 *
		 * @param int $id Comment ID.
		 */
		do_action( 'clean_comment_cache', $id );
	}

	wp_cache_set_comments_last_changed();
}

/**
 * Updates the comment cache of given comments.
 *
 * Will add the comments in $comments to the cache. If comment ID already exists
 * in the comment cache then it will not be updated. The comment is added to the
 * cache using the comment group with the key using the ID of the comments.
 *
 * @since 2.3.0
 * @since 4.4.0 Introduced the `$update_meta_cache` parameter.
 *
 * @param WP_Comment[] $comments          Array of comment objects
 * @param bool         $update_meta_cache Whether to update commentmeta cache. Default true.
 */
function update_comment_cache( $comments, $update_meta_cache = true ) {
	$data = array();
	foreach ( (array) $comments as $comment ) {
		$data[ $comment->comment_ID ] = $comment;
	}
	wp_cache_add_multiple( $data, 'comment' );

	if ( $update_meta_cache ) {
		// Avoid `wp_list_pluck()` in case `$comments` is passed by reference.
		$comment_ids = array();
		foreach ( $comments as $comment ) {
			$comment_ids[] = $comment->comment_ID;
		}
		update_meta_cache( 'comment', $comment_ids );
	}
}

/**
 * Adds any comments from the given IDs to the cache that do not already exist in cache.
 *
 * @since 4.4.0
 * @since 6.1.0 This function is no longer marked as "private".
 * @since 6.3.0 Use wp_lazyload_comment_meta() for lazy-loading of comment meta.
 *
 * @see update_comment_cache()
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param int[] $comment_ids       Array of comment IDs.
 * @param bool  $update_meta_cache Optional. Whether to update the meta cache. Default true.
 */
function _prime_comment_caches( $comment_ids, $update_meta_cache = true ) {
	global $wpdb;

	$non_cached_ids = _get_non_cached_ids( $comment_ids, 'comment' );
	if ( ! empty( $non_cached_ids ) ) {
		$fresh_comments = $wpdb->get_results( sprintf( "SELECT $wpdb->comments.* FROM $wpdb->comments WHERE comment_ID IN (%s)", implode( ',', array_map( 'intval', $non_cached_ids ) ) ) );

		update_comment_cache( $fresh_comments, false );
	}

	if ( $update_meta_cache ) {
		wp_lazyload_comment_meta( $comment_ids );
	}
}

//
// Internal.
//

/**
 * Closes comments on old posts on the fly, without any extra DB queries. Hooked to the_posts.
 *
 * @since 2.7.0
 * @access private
 *
 * @param WP_Post  $posts Post data object.
 * @param WP_Query $query Query object.
 * @return array
 */
function _close_comments_for_old_posts( $posts, $query ) {
	if ( empty( $posts ) || ! $query->is_singular() || ! get_option( 'close_comments_for_old_posts' ) ) {
		return $posts;
	}

	/**
	 * Filters the list of post types to automatically close comments for.
	 *
	 * @since 3.2.0
	 *
	 * @param string[] $post_types An array of post type names.
	 */
	$post_types = apply_filters( 'close_comments_for_post_types', array( 'post' ) );
	if ( ! in_array( $posts[0]->post_type, $post_types, true ) ) {
		return $posts;
	}

	$days_old = (int) get_option( 'close_comments_days_old' );
	if ( ! $days_old ) {
		return $posts;
	}

	if ( time() - strtotime( $posts[0]->post_date_gmt ) > ( $days_old * DAY_IN_SECONDS ) ) {
		$posts[0]->comment_status = 'closed';
		$posts[0]->ping_status    = 'closed';
	}

	return $posts;
}

/**
 * Closes comments on an old post. Hooked to comments_open and pings_open.
 *
 * @since 2.7.0
 * @access private
 *
 * @param bool $open    Comments open or closed.
 * @param int  $post_id Post ID.
 * @return bool $open
 */
function _close_comments_for_old_post( $open, $post_id ) {
	if ( ! $open ) {
		return $open;
	}

	if ( ! get_option( 'close_comments_for_old_posts' ) ) {
		return $open;
	}

	$days_old = (int) get_option( 'close_comments_days_old' );
	if ( ! $days_old ) {
		return $open;
	}

	$post = get_post( $post_id );

	/** This filter is documented in wp-includes/comment.php */
	$post_types = apply_filters( 'close_comments_for_post_types', array( 'post' ) );
	if ( ! in_array( $post->post_type, $post_types, true ) ) {
		return $open;
	}

	// Undated drafts should not show up as comments closed.
	if ( '0000-00-00 00:00:00' === $post->post_date_gmt ) {
		return $open;
	}

	if ( time() - strtotime( $post->post_date_gmt ) > ( $days_old * DAY_IN_SECONDS ) ) {
		return false;
	}

	return $open;
}

/**
 * Handles the submission of a comment, usually posted to wp-comments-post.php via a comment form.
 *
 * This function expects unslashed data, as opposed to functions such as `wp_new_comment()` which
 * expect slashed data.
 *
 * @since 4.4.0
 *
 * @param array $comment_data {
 *     Comment data.
 *
 *     @type string|int $comment_post_ID             The ID of the post that relates to the comment.
 *     @type string     $author                      The name of the comment author.
 *     @type string     $email                       The comment author email address.
 *     @type string     $url                         The comment author URL.
 *     @type string     $comment                     The content of the comment.
 *     @type string|int $comment_parent              The ID of this comment's parent, if any. Default 0.
 *     @type string     $_wp_unfiltered_html_comment The nonce value for allowing unfiltered HTML.
 * }
 * @return WP_Comment|WP_Error A WP_Comment object on success, a WP_Error object on failure.
 */
function wp_handle_comment_submission( $comment_data ) {
	$comment_post_id      = 0;
	$comment_author       = '';
	$comment_author_email = '';
	$comment_author_url   = '';
	$comment_content      = '';
	$comment_parent       = 0;
	$user_id              = 0;

	if ( isset( $comment_data['comment_post_ID'] ) ) {
		$comment_post_id = (int) $comment_data['comment_post_ID'];
	}
	if ( isset( $comment_data['author'] ) && is_string( $comment_data['author'] ) ) {
		$comment_author = trim( strip_tags( $comment_data['author'] ) );
	}
	if ( isset( $comment_data['email'] ) && is_string( $comment_data['email'] ) ) {
		$comment_author_email = trim( $comment_data['email'] );
	}
	if ( isset( $comment_data['url'] ) && is_string( $comment_data['url'] ) ) {
		$comment_author_url = trim( $comment_data['url'] );
	}
	if ( isset( $comment_data['comment'] ) && is_string( $comment_data['comment'] ) ) {
		$comment_content = trim( $comment_data['comment'] );
	}
	if ( isset( $comment_data['comment_parent'] ) ) {
		$comment_parent        = absint( $comment_data['comment_parent'] );
		$comment_parent_object = get_comment( $comment_parent );

		if (
			0 !== $comment_parent &&
			(
				! $comment_parent_object instanceof WP_Comment ||
				0 === (int) $comment_parent_object->comment_approved
			)
		) {
			/**
			 * Fires when a comment reply is attempted to an unapproved comment.
			 *
			 * @since 6.2.0
			 *
			 * @param int $comment_post_id Post ID.
			 * @param int $comment_parent  Parent comment ID.
			 */
			do_action( 'comment_reply_to_unapproved_comment', $comment_post_id, $comment_parent );

			return new WP_Error( 'comment_reply_to_unapproved_comment', __( 'Sorry, replies to unapproved comments are not allowed.' ), 403 );
		}
	}

	$post = get_post( $comment_post_id );

	if ( empty( $post->comment_status ) ) {

		/**
		 * Fires when a comment is attempted on a post that does not exist.
		 *
		 * @since 1.5.0
		 *
		 * @param int $comment_post_id Post ID.
		 */
		do_action( 'comment_id_not_found', $comment_post_id );

		return new WP_Error( 'comment_id_not_found' );

	}

	// get_post_status() will get the parent status for attachments.
	$status = get_post_status( $post );

	if ( ( 'private' === $status ) && ! current_user_can( 'read_post', $comment_post_id ) ) {
		return new WP_Error( 'comment_id_not_found' );
	}

	$status_obj = get_post_status_object( $status );

	if ( ! comments_open( $comment_post_id ) ) {

		/**
		 * Fires when a comment is attempted on a post that has comments closed.
		 *
		 * @since 1.5.0
		 *
		 * @param int $comment_post_id Post ID.
		 */
		do_action( 'comment_closed', $comment_post_id );

		return new WP_Error( 'comment_closed', __( 'Sorry, comments are closed for this item.' ), 403 );

	} elseif ( 'trash' === $status ) {

		/**
		 * Fires when a comment is attempted on a trashed post.
		 *
		 * @since 2.9.0
		 *
		 * @param int $comment_post_id Post ID.
		 */
		do_action( 'comment_on_trash', $comment_post_id );

		return new WP_Error( 'comment_on_trash' );

	} elseif ( ! $status_obj->public && ! $status_obj->private ) {

		/**
		 * Fires when a comment is attempted on a post in draft mode.
		 *
		 * @since 1.5.1
		 *
		 * @param int $comment_post_id Post ID.
		 */
		do_action( 'comment_on_draft', $comment_post_id );

		if ( current_user_can( 'read_post', $comment_post_id ) ) {
			return new WP_Error( 'comment_on_draft', __( 'Sorry, comments are not allowed for this item.' ), 403 );
		} else {
			return new WP_Error( 'comment_on_draft' );
		}
	} elseif ( post_password_required( $comment_post_id ) ) {

		/**
		 * Fires when a comment is attempted on a password-protected post.
		 *
		 * @since 2.9.0
		 *
		 * @param int $comment_post_id Post ID.
		 */
		do_action( 'comment_on_password_protected', $comment_post_id );

		return new WP_Error( 'comment_on_password_protected' );

	} else {
		/**
		 * Fires before a comment is posted.
		 *
		 * @since 2.8.0
		 *
		 * @param int $comment_post_id Post ID.
		 */
		do_action( 'pre_comment_on_post', $comment_post_id );
	}

	// If the user is logged in.
	$user = wp_get_current_user();
	if ( $user->exists() ) {
		if ( empty( $user->display_name ) ) {
			$user->display_name = $user->user_login;
		}

		$comment_author       = $user->display_name;
		$comment_author_email = $user->user_email;
		$comment_author_url   = $user->user_url;
		$user_id              = $user->ID;

		if ( current_user_can( 'unfiltered_html' ) ) {
			if ( ! isset( $comment_data['_wp_unfiltered_html_comment'] )
				|| ! wp_verify_nonce( $comment_data['_wp_unfiltered_html_comment'], 'unfiltered-html-comment_' . $comment_post_id )
			) {
				kses_remove_filters(); // Start with a clean slate.
				kses_init_filters();   // Set up the filters.
				remove_filter( 'pre_comment_content', 'wp_filter_post_kses' );
				add_filter( 'pre_comment_content', 'wp_filter_kses' );
			}
		}
	} else {
		if ( get_option( 'comment_registration' ) ) {
			return new WP_Error( 'not_logged_in', __( 'Sorry, you must be logged in to comment.' ), 403 );
		}
	}

	$comment_type = 'comment';

	if ( get_option( 'require_name_email' ) && ! $user->exists() ) {
		if ( '' == $comment_author_email || '' == $comment_author ) {
			return new WP_Error( 'require_name_email', __( '<strong>Error:</strong> Please fill the required fields.' ), 200 );
		} elseif ( ! is_email( $comment_author_email ) ) {
			return new WP_Error( 'require_valid_email', __( '<strong>Error:</strong> Please enter a valid email address.' ), 200 );
		}
	}

	$commentdata = array(
		'comment_post_ID' => $comment_post_id,
	);

	$commentdata += compact(
		'comment_author',
		'comment_author_email',
		'comment_author_url',
		'comment_content',
		'comment_type',
		'comment_parent',
		'user_id'
	);

	/**
	 * Filters whether an empty comment should be allowed.
	 *
	 * @since 5.1.0
	 *
	 * @param bool  $allow_empty_comment Whether to allow empty comments. Default false.
	 * @param array $commentdata         Array of comment data to be sent to wp_insert_comment().
	 */
	$allow_empty_comment = apply_filters( 'allow_empty_comment', false, $commentdata );
	if ( '' === $comment_content && ! $allow_empty_comment ) {
		return new WP_Error( 'require_valid_comment', __( '<strong>Error:</strong> Please type your comment text.' ), 200 );
	}

	$check_max_lengths = wp_check_comment_data_max_lengths( $commentdata );
	if ( is_wp_error( $check_max_lengths ) ) {
		return $check_max_lengths;
	}

	$comment_id = wp_new_comment( wp_slash( $commentdata ), true );
	if ( is_wp_error( $comment_id ) ) {
		return $comment_id;
	}

	if ( ! $comment_id ) {
		return new WP_Error( 'comment_save_error', __( '<strong>Error:</strong> The comment could not be saved. Please try again later.' ), 500 );
	}

	return get_comment( $comment_id );
}

/**
 * Registers the personal data exporter for comments.
 *
 * @since 4.9.6
 *
 * @param array[] $exporters An array of personal data exporters.
 * @return array[] An array of personal data exporters.
 */
function wp_register_comment_personal_data_exporter( $exporters ) {
	$exporters['wordpress-comments'] = array(
		'exporter_friendly_name' => __( 'WordPress Comments' ),
		'callback'               => 'wp_comments_personal_data_exporter',
	);

	return $exporters;
}

/**
 * Finds and exports personal data associated with an email address from the comments table.
 *
 * @since 4.9.6
 *
 * @param string $email_address The comment author email address.
 * @param int    $page          Comment page number.
 * @return array {
 *     An array of personal data.
 *
 *     @type array[] $data An array of personal data arrays.
 *     @type bool    $done Whether the exporter is finished.
 * }
 */
function wp_comments_personal_data_exporter( $email_address, $page = 1 ) {
	// Limit us to 500 comments at a time to avoid timing out.
	$number = 500;
	$page   = (int) $page;

	$data_to_export = array();

	$comments = get_comments(
		array(
			'author_email'              => $email_address,
			'number'                    => $number,
			'paged'                     => $page,
			'orderby'                   => 'comment_ID',
			'order'                     => 'ASC',
			'update_comment_meta_cache' => false,
		)
	);

	$comment_prop_to_export = array(
		'comment_author'       => __( 'Comment Author' ),
		'comment_author_email' => __( 'Comment Author Email' ),
		'comment_author_url'   => __( 'Comment Author URL' ),
		'comment_author_IP'    => __( 'Comment Author IP' ),
		'comment_agent'        => __( 'Comment Author User Agent' ),
		'comment_date'         => __( 'Comment Date' ),
		'comment_content'      => __( 'Comment Content' ),
		'comment_link'         => __( 'Comment URL' ),
	);

	foreach ( (array) $comments as $comment ) {
		$comment_data_to_export = array();

		foreach ( $comment_prop_to_export as $key => $name ) {
			$value = '';

			switch ( $key ) {
				case 'comment_author':
				case 'comment_author_email':
				case 'comment_author_url':
				case 'comment_author_IP':
				case 'comment_agent':
				case 'comment_date':
					$value = $comment->{$key};
					break;

				case 'comment_content':
					$value = get_comment_text( $comment->comment_ID );
					break;

				case 'comment_link':
					$value = get_comment_link( $comment->comment_ID );
					$value = sprintf(
						'<a href="%s" target="_blank" rel="noopener">%s</a>',
						esc_url( $value ),
						esc_html( $value )
					);
					break;
			}

			if ( ! empty( $value ) ) {
				$comment_data_to_export[] = array(
					'name'  => $name,
					'value' => $value,
				);
			}
		}

		$data_to_export[] = array(
			'group_id'          => 'comments',
			'group_label'       => __( 'Comments' ),
			'group_description' => __( 'User&#8217;s comment data.' ),
			'item_id'           => "comment-{$comment->comment_ID}",
			'data'              => $comment_data_to_export,
		);
	}

	$done = count( $comments ) < $number;

	return array(
		'data' => $data_to_export,
		'done' => $done,
	);
}

/**
 * Registers the personal data eraser for comments.
 *
 * @since 4.9.6
 *
 * @param array $erasers An array of personal data erasers.
 * @return array An array of personal data erasers.
 */
function wp_register_comment_personal_data_eraser( $erasers ) {
	$erasers['wordpress-comments'] = array(
		'eraser_friendly_name' => __( 'WordPress Comments' ),
		'callback'             => 'wp_comments_personal_data_eraser',
	);

	return $erasers;
}

/**
 * Erases personal data associated with an email address from the comments table.
 *
 * @since 4.9.6
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param string $email_address The comment author email address.
 * @param int    $page          Comment page number.
 * @return array {
 *     Data removal results.
 *
 *     @type bool     $items_removed  Whether items were actually removed.
 *     @type bool     $items_retained Whether items were retained.
 *     @type string[] $messages       An array of messages to add to the personal data export file.
 *     @type bool     $done           Whether the eraser is finished.
 * }
 */
function wp_comments_personal_data_eraser( $email_address, $page = 1 ) {
	global $wpdb;

	if ( empty( $email_address ) ) {
		return array(
			'items_removed'  => false,
			'items_retained' => false,
			'messages'       => array(),
			'done'           => true,
		);
	}

	// Limit us to 500 comments at a time to avoid timing out.
	$number         = 500;
	$page           = (int) $page;
	$items_removed  = false;
	$items_retained = false;

	$comments = get_comments(
		array(
			'author_email'       => $email_address,
			'number'             => $number,
			'paged'              => $page,
			'orderby'            => 'comment_ID',
			'order'              => 'ASC',
			'include_unapproved' => true,
		)
	);

	/* translators: Name of a comment's author after being anonymized. */
	$anon_author = __( 'Anonymous' );
	$messages    = array();

	foreach ( (array) $comments as $comment ) {
		$anonymized_comment                         = array();
		$anonymized_comment['comment_agent']        = '';
		$anonymized_comment['comment_author']       = $anon_author;
		$anonymized_comment['comment_author_email'] = '';
		$anonymized_comment['comment_author_IP']    = wp_privacy_anonymize_data( 'ip', $comment->comment_author_IP );
		$anonymized_comment['comment_author_url']   = '';
		$anonymized_comment['user_id']              = 0;

		$comment_id = (int) $comment->comment_ID;

		/**
		 * Filters whether to anonymize the comment.
		 *
		 * @since 4.9.6
		 *
		 * @param bool|string $anon_message       Whether to apply the comment anonymization (bool) or a custom
		 *                                        message (string). Default true.
		 * @param WP_Comment  $comment            WP_Comment object.
		 * @param array       $anonymized_comment Anonymized comment data.
		 */
		$anon_message = apply_filters( 'wp_anonymize_comment', true, $comment, $anonymized_comment );

		if ( true !== $anon_message ) {
			if ( $anon_message && is_string( $anon_message ) ) {
				$messages[] = esc_html( $anon_message );
			} else {
				/* translators: %d: Comment ID. */
				$messages[] = sprintf( __( 'Comment %d contains personal data but could not be anonymized.' ), $comment_id );
			}

			$items_retained = true;

			continue;
		}

		$args = array(
			'comment_ID' => $comment_id,
		);

		$updated = $wpdb->update( $wpdb->comments, $anonymized_comment, $args );

		if ( $updated ) {
			$items_removed = true;
			clean_comment_cache( $comment_id );
		} else {
			$items_retained = true;
		}
	}

	$done = count( $comments ) < $number;

	return array(
		'items_removed'  => $items_removed,
		'items_retained' => $items_retained,
		'messages'       => $messages,
		'done'           => $done,
	);
}

/**
 * Sets the last changed time for the 'comment' cache group.
 *
 * @since 5.0.0
 */
function wp_cache_set_comments_last_changed() {
	wp_cache_set_last_changed( 'comment' );
}

/**
 * Updates the comment type for a batch of comments.
 *
 * @since 5.5.0
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 */
function _wp_batch_update_comment_type() {
	global $wpdb;

	$lock_name = 'update_comment_type.lock';

	// Try to lock.
	$lock_result = $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO `$wpdb->options` ( `option_name`, `option_value`, `autoload` ) VALUES (%s, %s, 'no') /* LOCK */", $lock_name, time() ) );

	if ( ! $lock_result ) {
		$lock_result = get_option( $lock_name );

		// Bail if we were unable to create a lock, or if the existing lock is still valid.
		if ( ! $lock_result || ( $lock_result > ( time() - HOUR_IN_SECONDS ) ) ) {
			wp_schedule_single_event( time() + ( 5 * MINUTE_IN_SECONDS ), 'wp_update_comment_type_batch' );
			return;
		}
	}

	// Update the lock, as by this point we've definitely got a lock, just need to fire the actions.
	update_option( $lock_name, time() );

	// Check if there's still an empty comment type.
	$empty_comment_type = $wpdb->get_var(
		"SELECT comment_ID FROM $wpdb->comments
		WHERE comment_type = ''
		LIMIT 1"
	);

	// No empty comment type, we're done here.
	if ( ! $empty_comment_type ) {
		update_option( 'finished_updating_comment_type', true );
		delete_option( $lock_name );
		return;
	}

	// Empty comment type found? We'll need to run this script again.
	wp_schedule_single_event( time() + ( 2 * MINUTE_IN_SECONDS ), 'wp_update_comment_type_batch' );

	/**
	 * Filters the comment batch size for updating the comment type.
	 *
	 * @since 5.5.0
	 *
	 * @param int $comment_batch_size The comment batch size. Default 100.
	 */
	$comment_batch_size = (int) apply_filters( 'wp_update_comment_type_batch_size', 100 );

	// Get the IDs of the comments to update.
	$comment_ids = $wpdb->get_col(
		$wpdb->prepare(
			"SELECT comment_ID
			FROM {$wpdb->comments}
			WHERE comment_type = ''
			ORDER BY comment_ID DESC
			LIMIT %d",
			$comment_batch_size
		)
	);

	if ( $comment_ids ) {
		$comment_id_list = implode( ',', $comment_ids );

		// Update the `comment_type` field value to be `comment` for the next batch of comments.
		$wpdb->query(
			"UPDATE {$wpdb->comments}
			SET comment_type = 'comment'
			WHERE comment_type = ''
			AND comment_ID IN ({$comment_id_list})" // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
		);

		// Make sure to clean the comment cache.
		clean_comment_cache( $comment_ids );
	}

	delete_option( $lock_name );
}

/**
 * In order to avoid the _wp_batch_update_comment_type() job being accidentally removed,
 * check that it's still scheduled while we haven't finished updating comment types.
 *
 * @ignore
 * @since 5.5.0
 */
function _wp_check_for_scheduled_update_comment_type() {
	if ( ! get_option( 'finished_updating_comment_type' ) && ! wp_next_scheduled( 'wp_update_comment_type_batch' ) ) {
		wp_schedule_single_event( time() + MINUTE_IN_SECONDS, 'wp_update_comment_type_batch' );
	}
}