files.js

'use strict';

const {google} = require('googleapis');
const path = require('path');
const fs = require('fs');

function getCredentials() {
  const filePath = path.join(__dirname, 'keys.json');
  if (fs.existsSync(filePath)) {
    return require(filePath);
  }
  if (process.env.CREDENTIALS) {
    return JSON.parse(process.env.CREDENTIALS);
  }
  throw new Error('Unable to load credentials');
}

async function getFiles () {
  const credentials = getCredentials();
  const client = await google.auth.getClient({
    credentials,
    scopes: 'https://www.googleapis.com/auth/drive.readonly'
  });
  const drive = google.drive({
    version: 'v2',
    auth: client
  });
  return drive.files.list();
}

exports.handler = function(event, context, callback) {
  console.log('DATE! ' + (new Date()));
  getFiles().then(res => {
    callback(null, {
      statusCode: 200,
      body: JSON.stringify(res.data)
    });
  }).catch(e => {
    callback(e);
  });

  // callback(null, {
  //   statusCode: 200,
  //   body: JSON.stringify({ foo: 'bar' })
  // });
}