e, `$hostname`, refers to the hostname
		 * of the URI specified in the `Update URI` header field.
		 *
		 * @since 6.1.0
		 *
		 * @param array|false $update {
		 *     The theme update data with the latest details. Default false.
		 *
		 *     @type string $id           Optional. ID of the theme for update purposes, should be a URI
		 *                                specified in the `Update URI` header field.
		 *     @type string $theme        Directory name of the theme.
		 *     @type string $version      The version of the theme.
		 *     @type string $url          The URL for details of the theme.
		 *     @type string $package      Optional. The update ZIP for the theme.
		 *     @type string $tested       Optional. The version of WordPress the theme is tested against.
		 *     @type string $requires_php Optional. The version of PHP which the theme requires.
		 *     @type bool   $autoupdate   Optional. Whether the theme should automatically update.
		 *     @type array  $translations {
		 *         Optional. List of translation updates for the theme.
		 *
		 *         @type string $language   The language the translation update is for.
		 *         @type string $version    The version of the theme this translation is for.
		 *                                  This is not the version of the language file.
		 *         @type string $updated    The update timestamp of the translation file.
		 *                                  Should be a date in the `YYYY-MM-DD HH:MM:SS` format.
		 *         @type string $package    The ZIP location containing the translation update.
		 *         @type string $autoupdate Whether the translation should be automatically installed.
		 *     }
		 * }
		 * @param array       $theme_data       Theme headers.
		 * @param string      $theme_stylesheet Theme stylesheet.
		 * @param string[]    $locales          Installed locales to look up translations for.
		 */
		$update = apply_filters( "update_themes_{$hostname}", false, $theme_data, $theme_stylesheet, $locales );

		if ( ! $update ) {
			continue;
		}

		$update = (object) $update;

		// Is it valid? We require at least a version.
		if ( ! isset( $update->version ) ) {
			continue;
		}

		// This should remain constant.
		$update->id = $theme_data['UpdateURI'];

		// WordPress needs the version field specified as 'new_version'.
		if ( ! isset( $update->new_version ) ) {
			$update->new_version = $update->version;
		}

		// Handle any translation updates.
		if ( ! empty( $update->translations ) ) {
			foreach ( $update->translations as $translation ) {
				if ( isset( $translation['language'], $translation['package'] ) ) {
					$translation['type'] = 'theme';
					$translation['slug'] = isset( $update->theme ) ? $update->theme : $update->id;

					$new_update->translations[] = $translation;
				}
			}
		}

		unset( $new_update->no_update[ $theme_stylesheet ], $new_update->response[ $theme_stylesheet ] );

		if ( version_compare( $update->new_version, $theme_data['Version'], '>' ) ) {
			$new_update->response[ $theme_stylesheet ] = (array) $update;
		} else {
			$new_update->no_update[ $theme_stylesheet ] = (array) $update;
		}
	}

	set_site_transient( 'update_themes', $new_update );
}

/**
 * Performs WordPress automatic background updates.
 *
 * Updates WordPress core plus any plugins and themes that have automatic updates enabled.
 *
 * @since 3.7.0
 */
function wp_maybe_auto_update() {
	require_once ABSPATH . 'wp-admin/includes/admin.php';
	require_once ABSPATH . 'wp-admin/includes/class-wp-upgrader.php';

	$upgrader = new WP_Automatic_Updater();
	$upgrader->run();
}

/**
 * Retrieves a list of all language updates available.
 *
 * @since 3.7.0
 *
 * @return object[] Array of translation objects that have available updates.
 */
function wp_get_translation_updates() {
	$updates    = array();
	$transients = array(
		'update_core'    => 'core',
		'update_plugins' => 'plugin',
		'update_themes'  => 'theme',
	);

	foreach ( $transients as $transient => $type ) {
		$transient = get_site_transient( $transient );

		if ( empty( $transient->translations ) ) {
			continue;
		}

		foreach ( $transient->translations as $translation ) {
			$updates[] = (object) $translation;
		}
	}

	return $updates;
}

/**
 * Collects counts and UI strings for available updates.
 *
 * @since 3.3.0
 *
 * @return array
 */
function wp_get_update_data() {
	$counts = array(
		'plugins'      => 0,
		'themes'       => 0,
		'wordpress'    => 0,
		'translations' => 0,
	);

	$plugins = current_user_can( 'update_plugins' );

	if ( $plugins ) {
		$update_plugins = get_site_transient( 'update_plugins' );

		if ( ! empty( $update_plugins->response ) ) {
			$counts['plugins'] = count( $update_plugins->response );
		}
	}

	$themes = current_user_can( 'update_themes' );

	if ( $themes ) {
		$update_themes = get_site_transient( 'update_themes' );

		if ( ! empty( $update_themes->response ) ) {
			$counts['themes'] = count( $update_themes->response );
		}
	}

	$core = current_user_can( 'update_core' );

	if ( $core && function_exists( 'get_core_updates' ) ) {
		$update_wordpress = get_core_updates( array( 'dismissed' => false ) );

		if ( ! empty( $update_wordpress )
			&& ! in_array( $update_wordpress[0]->response, array( 'development', 'latest' ), true )
			&& current_user_can( 'update_core' )
		) {
			$counts['wordpress'] = 1;
		}
	}

	if ( ( $core || $plugins || $themes ) && wp_get_translation_updates() ) {
		$counts['translations'] = 1;
	}

	$counts['total'] = $counts['plugins'] + $counts['themes'] + $counts['wordpress'] + $counts['translations'];
	$titles          = array();

	if ( $counts['wordpress'] ) {
		/* translators: %d: Number of available WordPress updates. */
		$titles['wordpress'] = sprintf( __( '%d WordPress Update' ), $counts['wordpress'] );
	}

	if ( $counts['plugins'] ) {
		/* translators: %d: Number of available plugin updates. */
		$titles['plugins'] = sprintf( _n( '%d Plugin Update', '%d Plugin Updates', $counts['plugins'] ), $counts['plugins'] );
	}

	if ( $counts['themes'] ) {
		/* translators: %d: Number of available theme updates. */
		$titles['themes'] = sprintf( _n( '%d Theme Update', '%d Theme Updates', $counts['themes'] ), $counts['themes'] );
	}

	if ( $counts['translations'] ) {
		$titles['translations'] = __( 'Translation Updates' );
	}

	$update_title = $titles ? esc_attr( implode( ', ', $titles ) ) : '';

	$update_data = array(
		'counts' => $counts,
		'title'  => $update_title,
	);
	/**
	 * Filters the returned array of update data for plugins, themes, and WordPress core.
	 *
	 * @since 3.5.0
	 *
	 * @param array $update_data {
	 *     Fetched update data.
	 *
	 *     @type array   $counts       An array of counts for available plugin, theme, and WordPress updates.
	 *     @type string  $update_title Titles of available updates.
	 * }
	 * @param array $titles An array of update counts and UI strings for available updates.
	 */
	return apply_filters( 'wp_get_update_data', $update_data, $titles );
}

/**
 * Determines whether core should be updated.
 *
 * @since 2.8.0
 *
 * @global string $wp_version The WordPress version string.
 */
function _maybe_update_core() {
	$current = get_site_transient( 'update_core' );

	if ( isset( $current->last_checked, $current->version_checked )
		&& 12 * HOUR_IN_SECONDS > ( time() - $current->last_checked )
		&& wp_get_wp_version() === $current->version_checked
	) {
		return;
	}

	wp_version_check();
}
/**
 * Checks the last time plugins were run before checking plugin versions.
 *
 * This might have been backported to WordPress 2.6.1 for performance reasons.
 * This is used for the wp-admin to check only so often instead of every page
 * load.
 *
 * @since 2.7.0
 * @access private
 */
function _maybe_update_plugins() {
	$current = get_site_transient( 'update_plugins' );

	if ( isset( $current->last_checked )
		&& 12 * HOUR_IN_SECONDS > ( time() - $current->last_checked )
	) {
		return;
	}

	wp_update_plugins();
}

/**
 * Checks themes versions only after a duration of time.
 *
 * This is for performance reasons to make sure that on the theme version
 * checker is not run on every page load.
 *
 * @since 2.7.0
 * @access private
 */
function _maybe_update_themes() {
	$current = get_site_transient( 'update_themes' );

	if ( isset( $current->last_checked )
		&& 12 * HOUR_IN_SECONDS > ( time() - $current->last_checked )
	) {
		return;
	}

	wp_update_themes();
}

/**
 * Schedules core, theme, and plugin update checks.
 *
 * @since 3.1.0
 */
function wp_schedule_update_checks() {
	if ( ! wp_next_scheduled( 'wp_version_check' ) && ! wp_installing() ) {
		wp_schedule_event( time(), 'twicedaily', 'wp_version_check' );
	}

	if ( ! wp_next_scheduled( 'wp_update_plugins' ) && ! wp_installing() ) {
		wp_schedule_event( time(), 'twicedaily', 'wp_update_plugins' );
	}

	if ( ! wp_next_scheduled( 'wp_update_themes' ) && ! wp_installing() ) {
		wp_schedule_event( time(), 'twicedaily', 'wp_update_themes' );
	}
}

/**
 * Clears existing update caches for plugins, themes, and core.
 *
 * @since 4.1.0
 */
function wp_clean_update_cache() {
	if ( function_exists( 'wp_clean_plugins_cache' ) ) {
		wp_clean_plugins_cache();
	} else {
		delete_site_transient( 'update_plugins' );
	}

	wp_clean_themes_cache();

	delete_site_transient( 'update_core' );
}

/**
 * Schedules the removal of all contents in the temporary backup directory.
 *
 * @since 6.3.0
 */
function wp_delete_all_temp_backups() {
	/*
	 * Check if there is a lock, or if currently performing an Ajax request,
	 * in which case there is a chance an update is running.
	 * Reschedule for an hour from now and exit early.
	 */
	if ( get_option( 'core_updater.lock' ) || get_option( 'auto_updater.lock' ) || wp_doing_ajax() ) {
		wp_schedule_single_event( time() + HOUR_IN_SECONDS, 'wp_delete_temp_updater_backups' );
		return;
	}

	// This action runs on shutdown to make sure there are no plugin updates currently running.
	add_action( 'shutdown', '_wp_delete_all_temp_backups' );
}

/**
 * Deletes all contents in the temporary backup directory.
 *
 * @since 6.3.0
 *
 * @access private
 *
 * @global WP_Filesystem_Base $wp_filesystem WordPress filesystem subclass.
 */
function _wp_delete_all_temp_backups() {
	global $wp_filesystem;

	if ( ! function_exists( 'WP_Filesystem' ) ) {
		require_once ABSPATH . '/wp-admin/includes/file.php';
	}

	ob_start();
	$credentials = request_filesystem_credentials( '' );
	ob_end_clean();

	if ( false === $credentials || ! WP_Filesystem( $credentials ) ) {
		wp_trigger_error( __FUNCTION__, __( 'Could not access filesystem.' ) );
		return;
	}

	if ( ! $wp_filesystem->wp_content_dir() ) {
		wp_trigger_error(
			__FUNCTION__,
			/* translators: %s: Directory name. */
			sprintf( __( 'Unable to locate WordPress content directory (%s).' ), 'wp-content' )
		);
		return;
	}

	$temp_backup_dir = $wp_filesystem->wp_content_dir() . 'upgrade-temp-backup/';
	$dirlist         = $wp_filesystem->dirlist( $temp_backup_dir );
	$dirlist         = $dirlist ? $dirlist : array();

	foreach ( array_keys( $dirlist ) as $dir ) {
		if ( '.' === $dir || '..' === $dir ) {
			continue;
		}

		$wp_filesystem->delete( $temp_backup_dir . $dir, true );
	}
}

if ( ( ! is_main_site() && ! is_network_admin() ) || wp_doing_ajax() ) {
	return;
}

add_action( 'admin_init', '_maybe_update_core' );
add_action( 'wp_version_check', 'wp_version_check' );

add_action( 'load-plugins.php', 'wp_update_plugins' );
add_action( 'load-update.php', 'wp_update_plugins' );
add_action( 'load-update-core.php', 'wp_update_plugins' );
add_action( 'admin_init', '_maybe_update_plugins' );
add_action( 'wp_update_plugins', 'wp_update_plugins' );

add_action( 'load-themes.php', 'wp_update_themes' );
add_action( 'load-update.php', 'wp_update_themes' );
add_action( 'load-update-core.php', 'wp_update_themes' );
add_action( 'admin_init', '_maybe_update_themes' );
add_action( 'wp_update_themes', 'wp_update_themes' );

add_action( 'update_option_WPLANG', 'wp_clean_update_cache', 10, 0 );

add_action( 'wp_maybe_auto_update', 'wp_maybe_auto_update' );

add_action( 'init', 'wp_schedule_update_checks' );

add_action( 'wp_delete_temp_updater_backups', 'wp_delete_all_temp_backups' );