Thinking through how we might fetch email messages from google's api

gmail-sync.js

const { google } = require('googleapis');
const moment = require('moment');

// Assuming we have authed against Google's API and we have permission...
const getRecentEmails = (auth, from, daysAgo = 14) => {
  const gmail = google.gmail({ version: 'v1', auth });
  const date = moment().subtract(daysAgo, 'days').format('YYYY/MM/DD');
   
  gmail.users.messages.list({ userId: 'me', q: `label:inbox from:${from} newer:${date}` }, handleListResponse(gmail));
};

const handleListResponse = (gmail) => {
  return (err, res) => {
    if (err != null) {
      console.error(err);
      return;
    }
    
    const messages = res.data.messages;
    
    if (!messages.length) {
      console.log('no results found');
      return;
    }
    
    messages.forEach(({ id }) => {
      gmail.users.messages.get({ userId: 'me', id }, handleMessageResponse(gmail));
    });
  };
};

const fromHeader = (name, { headers }) => headers.find((header) => header.name === name);

const fromMimeType = (mimeType, { parts }) => parts.find((part) => part.mimeType === mimeType);

const fromBase64 = (string) => string != null ? Buffer.from(string, 'base64') : null;

const handleMessageResponse = (gmail) => {
  return (err, res) => {
    if (err != null) {
      console.error(err);
      return;
    }

    const { message } = res.data;

    if (message == null) {
      console.log('message not found');
      return;
    }

    const { id, payload, snippet } = message;

    // Dangerously assume email mimeType is multipart
    const textBody = fromBase64(fromMimeType(payload, 'text/plain'));
    const htmlBody = fromBase64(fromMimeType(payload, 'text/html'));

    const subject = fromHeader(payload, 'subject');
    const sentDate = fromHeader(payload, 'date');

    console.log({
      id,
      snippet,  // NOTE: snippet (preview text) comes accross the wire as plain text
      subject,
      sentDate,
      textBody,
      htmlBody,
    });
  };
};