// Test file that aquires authorization then exports a list of gdoc files as text from My Drive to local directory

exportTest4.js

// Test file that aquires authorization then exports a list of gdoc files as text from My Drive to local directory

const fs = require('fs');
const fsp = fs.promises;


const path = require('path');
const process = require('process');
const {authenticate} = require('@google-cloud/local-auth');
const {google} = require('googleapis');

// If modifying these scopes, delete token.json.
const SCOPES = ['https://www.googleapis.com/auth/drive'];


// The file token.json stores the user's access and refresh tokens, and is
// created automatically when the authorization flow completes for the first
// time.
const TOKEN_PATH = path.join(process.cwd(), 'DownloadFileToken.json');
const CREDENTIALS_PATH = 'C:\\googleDriveDev\\credentials.json';

/**
 * Reads previously authorized credentials from the save file.
 *
 * @return {Promise<OAuth2Client|null>}
 */
async function loadSavedCredentialsIfExist() {
    try {
        const content = await fsp.readFile(TOKEN_PATH);
        const credentials = JSON.parse(content);
        return google.auth.fromJSON(credentials);
    } catch (err) {
        return null;
    }
}


/**
 * Serializes credentials to a file compatible with GoogleAUth.fromJSON.
 *
 * @param {OAuth2Client} client
 * @return {Promise<void>}
 */
async function saveCredentials(client) {
    const content = await fsp.readFile(CREDENTIALS_PATH);
    const keys = JSON.parse(content);
    const key = keys.installed || keys.web;
    const payload = JSON.stringify({
        type: 'authorized_user',
        client_id: key.client_id,
        client_secret: key.client_secret,
        refresh_token: client.credentials.refresh_token,
    });
    await fsp.writeFile(TOKEN_PATH, payload);
}

/**
 * Load or request or authorization to call APIs.
 *
 */
async function authorize() {
    let client = await loadSavedCredentialsIfExist();
    if (client) {
        return client;
    }
    client = await authenticate({
        scopes: SCOPES,
        keyfilePath: CREDENTIALS_PATH,
    });
    if (client.credentials) {
        await saveCredentials(client);
    }
    return client;
}


// Code that lists then exports files
async function listFilesAndExport(auth) {
    const drive = google.drive({ version: 'v3', auth });
  
    try {
      const res = await drive.files.list({
        corpora: 'user',
        pageSize: 100,
        q: `'11Sejh6XG-2WzycpcC-MaEmDQJc78LCFg' in parents and trashed=false`,
        fields: 'files(id, name)',
      });
      
      const files = res.data.files;
      
      if (files.length) {
        const fileIdentity = files.map(file => [file.id, file.name]);
        return fileIdentity;
      } else {
        console.log('No files found.');
        return [];
      }
    } catch (err) {
      console.error('The API returned an error:', err);
      throw err;
    }
  }
  
  async function exportTxtForFiles(auth) {
    try {
      const fileIdentity = await listFilesAndExport(auth);
      if (fileIdentity.length) {
        const service = google.drive({ version: 'v3', auth });
        for (const [fileId, fileName] of fileIdentity) {
          const result = await service.files.export({
            fileId: fileId,
            mimeType: 'text/plain',
          }, { responseType: 'stream' });
  
          const destFile = fs.createWriteStream(`C:\\erctest\\erctest3\\${fileName}.txt`);
          result.data
            .on('end', function () {
              console.log(`File "${fileName}" exported successfully.`);
            })
            .on('error', function (err) {
              console.error(err);
              throw err;
            })
            .pipe(destFile);
        }
      } else {
        console.log('No files to export.');
      }
    } catch (err) {
      console.error('Error exporting files:', err);
      throw err;
    }
  }
  
  authorize()
    .then(exportTxtForFiles)
    .catch(console.error);