const debug = require('debug')('talk:services:mailer');
const nodemailer = require('nodemailer');
const kue = require('./kue');
const i18n = require('./i18n');
const path = require('path');
const fs = require('fs-extra');
const _ = require('lodash');
const {TEMPLATE_LOCALS} = require('../middleware/staticTemplate');

const {
  SMTP_HOST,
  SMTP_USERNAME,
  SMTP_PORT,
  SMTP_PASSWORD,
  SMTP_FROM_ADDRESS,
  EMAIL_SUBJECT_PREFIX,
} = require('../config');

// load all the templates as strings
const templates = {
  data: {}
};

// load the templates per request during development
templates.render = async (name, format = 'txt', context) => {

  if (process.env.NODE_ENV === 'production') {

    // If we are in production mode, check the view cache.
    const view = _.get(templates.data, [name, format], null);
    if (view !== null) {
      return view(context);
    }
  }

  const filename = path.join(__dirname, 'email', [name, format, 'ejs'].join('.'));
  const file = await fs.readFile(filename, 'utf8');
  const view = _.template(file);

  if (process.env.NODE_ENV === 'production') {

    // If we are in production mode, fill the view cache.
    _.set(templates.data, [name, format], view);
  }

  return view(context);
};

const mailer = {};

// enabled is true when the required configuration is available. When testing
// is enabled, we will be simulating that emails are being sent, because in a
// production system, emails should and would be sent.
mailer.enabled = Boolean(
  SMTP_HOST &&
  SMTP_USERNAME &&
  SMTP_PASSWORD &&
  SMTP_FROM_ADDRESS
) || process.env.NODE_ENV === 'test';

if (mailer.enabled) {
  const options = {
    host: SMTP_HOST,
    auth: {
      user: SMTP_USERNAME,
      pass: SMTP_PASSWORD
    }
  };

  if (SMTP_PORT) {
    try {
      options.port = parseInt(SMTP_PORT);
    } catch (e) {
      throw new Error('TALK_SMTP_PORT is not an integer');
    }
  } else {
    options.port = 25;
  }

  mailer.transport = nodemailer.createTransport(options);
}

/**
 * Create the new Task kue.
 */
mailer.task = new kue.Task({
  name: 'mailer'
});

/**
 * send will create a new message and send it.
 */
mailer.send = async (options) => {
  if (!mailer.enabled) {
    const err = new Error('sending email is not enabled because required configuration is not available');
    console.warn(err);
    return;
  }

  // Create the new locals object and attach the static locals and the i18n
  // framework.
  const locals = _.merge({}, options.locals, TEMPLATE_LOCALS, {t: i18n.t});

  // Render the templates.
  const [
    html,
    text,
  ] = await Promise.all(['html', 'txt'].map((fmt) => {
    return templates.render(options.template, fmt, locals);
  }));

  // Create the job to send the email later.
  return mailer.task.create({
    title: 'Mail',
    message: {
      to: options.to,
      subject: `${EMAIL_SUBJECT_PREFIX} ${options.subject}`,
      text,
      html
    }
  });
};

/**
 * Start the queue processor for the mailer job.
 */
mailer.process = () => {

  debug(`Now processing ${mailer.task.name} jobs`);

  return mailer.task.process(({id, data}, done) => {
    debug(`Starting to send mail for Job[${id}]`);

    // Set the `from` field.
    data.message.from = SMTP_FROM_ADDRESS;

    // Actually send the email.
    mailer.transport.sendMail(data.message, (err) => {
      if (err) {
        debug(`Failed to send mail for Job[${id}]:`, err);
        return done(err);
      }

      debug(`Finished sending mail for Job[${id}]`);
      return done();
    });
  });
};

module.exports = mailer;