Spike on automatically saving Google Apps invoice attachment from Gmail into Google Drive using Google App Script

handle-google-apps-invoice.js

function myFunction() {
  var threads = GmailApp.search("label:inbox subject:'Google Enterprise: Your invoice is attached'");
  for (var threadIndex = 0 ; threadIndex < threads.length; threadIndex++) {
    var messages = threads[threadIndex].getMessages();
    if (messages.length == 0) {
      Logger.log('No messages found in thread.');
      return;
    }
    var message = messages[0];
    var attachments = message.getAttachments();
    if (attachments.length == 0) {
      Logger.log('No attachments found in message.');
      return;
    }
    var attachment = attachments[0];
    var datestamp = new Date().toISOString().substring(0,10);
    var filename = datestamp + ' Google Apps - Invoice ' + attachment.getName();
    var folders = DriveApp.getFoldersByName('Invoices and receipts');
    if (!folders.hasNext()) {
      return;
    }
    var folder = folders.next();
    Logger.log('Saving attachment ' + attachment.getName() + ' to Drive with name ' + filename + '.');
    folder.createFile(attachment.setName(filename));
    Logger.log('Done.');
  }
}