wpmu_delete_blog( int $blog_id, bool $drop = false )

function wpmu_delete_blog( $blog_id, $drop = false ) {
	global $wpdb;

	$switch = false;
	if ( get_current_blog_id() != $blog_id ) {
		$switch = true;
		switch_to_blog( $blog_id );
	}

	$blog = get_site( $blog_id );
	/**
	 * Fires before a site is deleted.
	 *
	 * @since WP-MU (3.0.0)
	 *
	 * @param int  $blog_id The site ID.
	 * @param bool $drop    True if site's table should be dropped. Default is false.
	 */
	do_action( 'delete_blog', $blog_id, $drop );

	$users = get_users( array( 'blog_id' => $blog_id, 'fields' => 'ids' ) );

	// Remove users from this blog.
	if ( ! empty( $users ) ) {
		foreach ( $users as $user_id ) {
			remove_user_from_blog( $user_id, $blog_id );
		}
	}

	update_blog_status( $blog_id, 'deleted', 1 );

	$current_network = get_network();

	// If a full blog object is not available, do not destroy anything.
	if ( $drop && ! $blog ) {
		$drop = false;
	}

	// Don't destroy the initial, main, or root blog.
	if ( $drop && ( 1 == $blog_id || is_main_site( $blog_id ) || ( $blog->path == $current_network->path && $blog->domain == $current_network->domain ) ) ) {
		$drop = false;
	}

	$upload_path = trim( get_option( 'upload_path' ) );

	// If ms_files_rewriting is enabled and upload_path is empty, wp_upload_dir is not reliable.
	if ( $drop && get_site_option( 'ms_files_rewriting' ) && empty( $upload_path ) ) {
		$drop = false;
	}

	if ( $drop ) {
		$uploads = wp_get_upload_dir();

		$tables = $wpdb->tables( 'blog' );
		/**
		 * Filters the tables to drop when the site is deleted.
		 *
		 * @since WP-MU (3.0.0)
		 *
		 * @param array $tables  The site tables to be dropped.
		 * @param int   $blog_id The ID of the site to drop tables for.
		 */
		$drop_tables = apply_filters( 'wpmu_drop_tables', $tables, $blog_id );

		foreach ( (array) $drop_tables as $table ) {
			$wpdb->query( "DROP TABLE IF EXISTS `$table`" );
		}

		$wpdb->delete( $wpdb->blogs, array( 'blog_id' => $blog_id ) );

		/**
		 * Filters the upload base directory to delete when the site is deleted.
		 *
		 * @since WP-MU (3.0.0)
		 *
		 * @param string $uploads['basedir'] Uploads path without subdirectory. @see wp_upload_dir()
		 * @param int    $blog_id            The site ID.
		 */
		$dir = apply_filters( 'wpmu_delete_blog_upload_dir', $uploads['basedir'], $blog_id );
		$dir = rtrim( $dir, DIRECTORY_SEPARATOR );
		$top_dir = $dir;
		$stack = array($dir);
		$index = 0;

		while ( $index < count( $stack ) ) {
			// Get indexed directory from stack
			$dir = $stack[$index];

			$dh = @opendir( $dir );
			if ( $dh ) {
				while ( ( $file = @readdir( $dh ) ) !== false ) {
					if ( $file == '.' || $file == '..' )
						continue;

					if ( @is_dir( $dir . DIRECTORY_SEPARATOR . $file ) ) {
						$stack[] = $dir . DIRECTORY_SEPARATOR . $file;
					} elseif ( @is_file( $dir . DIRECTORY_SEPARATOR . $file ) ) {
						@unlink( $dir . DIRECTORY_SEPARATOR . $file );
					}
				}
				@closedir( $dh );
			}
			$index++;
		}

		$stack = array_reverse( $stack ); // Last added dirs are deepest
		foreach ( (array) $stack as $dir ) {
			if ( $dir != $top_dir)
			@rmdir( $dir );
		}

		clean_blog_cache( $blog );
	}

	/**
	 * Fires after the site is deleted from the network.
	 *
	 * @since WP-4.8.0
	 *
	 * @param int  $blog_id The site ID.
	 * @param bool $drop    True if site's tables should be dropped. Default is false.
	 */
	do_action( 'deleted_blog', $blog_id, $drop );

	if ( $switch )
		restore_current_blog();
}