const {Logging} = require('@google-cloud/logging');
const { GoogleAuth, JWT, Impersonated, ImpersonatedOptions  } = require('google-auth-library');
const { Storage } = require('@google-cloud/storage');
const {Logging} = require('@google-cloud/logging');

var svcAccountFile = 'svc_account.json';
var project_id = 'yourprojectID';


const keys = require(svcAccountFile);

// create a sourceCredential
let saclient = new JWT(
  keys.client_email,
  null,
  keys.private_key,
  ['https://www.googleapis.com/auth/cloud-platform', 'https://www.googleapis.com/auth/iam'],
);


// Use that to impersonate the targetPrincipal
let targetClient = new Impersonated({
  sourceClient: saclient,
  targetPrincipal: "target@anotherproject.iam.gserviceaccount.com",
  lifetime: 30,
  delegates: [],
  targetScopes: ["https://www.googleapis.com/auth/cloud-platform"]
});

// At this point you can use the client as any other:

// 1. Acquire Headers
const authHeaders = await targetClient.getRequestHeaders();
console.log(authHeaders);

// 2. Use client in authorized session 
targetClient.getAccessToken().then(res => {
  let url = 'https://www.googleapis.com/storage/v1/b?project=' + project_id
  targetClient.requestAsync({ url }).then(resp => {
    console.log(resp.data.items[0]);
  }).catch(function (error) {
    console.error('Unable to list buckets: ' + error);
  });
});

// 3. Use client with GCP Service 
const { Logging } = require('@google-cloud/logging');

const log = logging.log('mylog');
const text = 'Hello, world!';
const metadata = {
  resource: {type: 'global'},
};
const entry = log.entry(metadata, text);
await log.write(entry);
console.log(`Logged: ${text}`);