You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: externalcontrollerupdater.go
    path of file: ./repos/juju/api/controller/externalcontrollerupdater
    
    the code of the file until where you have to start completion: // Copyright 2017 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package externalcontrollerupdater

import (
	"github.com/juju/errors"
	"github.com/juju/names/v5"

	"github.com/juju/juju/api/base"
	apiwatcher "github.com/juju/juju/api/watcher"
	apiservererrors "github.com/juju/juju/apiserver/errors"
	"github.com/juju/juju/core/crossmodel"
	"github.com/juju/juju/core/watcher"
	"github.com/juju/juju/rpc/params"
)

const Facade = "ExternalControllerUpdater"

// Client provides access to the ExternalControllerUpdater API facade.
type Client struct {
	facade base.FacadeCaller
}

// New creates a new client-side ExternalControllerUpdater facade.
func New(caller base.APICaller) *Client {
	return &Client{base.NewFacadeCaller(caller, Facade)}
}

// Wat
    
func (c *Client) ExternalControllerInfo(controllerUUID string) (*crossmodel.ControllerInfo, error) {
	if !names.IsValidController(controllerUUID) {
		return nil, errors.NotValidf("controller UUID %q", controllerUUID)
	}
	controllerTag := names.NewControllerTag(controllerUUID)
	args := params.Entities{[]params.Entity{{
		Tag: controllerTag.String(),
	}}}
	var results params.ExternalControllerInfoResults
	err := c.facade.FacadeCall("ExternalControllerInfo", args, &results)
	if err != nil {
		return nil, errors.Trace(err)
	}
	if len(results.Results) != 1 {
		return nil, errors.Errorf("expected 1 result, got %d", len(results.Results))
	}
	result := results.Results[0]
	if result.Error != nil {
		err := apiservererrors.RestoreError(result.Error)
		return nil, errors.Trace(err)
	}
	return &crossmodel.ControllerInfo{
		ControllerTag: controllerTag,
		Alias:         result.Result.Alias,
		Addrs:         result.Result.Addrs,
		CACert:        result.Result.CACert,
	}, nil
}