#5_write_csv.js

const createCsvWriter = require('csv-writer').createObjectCsvWriter;
const moment = require('moment');

/**
 * Converts a string date to a DATETIME string that can be used
 * in BigQuery tables
 * @param {string} date Date in string Format 'YYYY-MM-DD' 
 */
const format = (date) => {
  return `${moment(new Date(date)).format('YYYY-MM-DD hh:mm:ss')}.000000`;
}

/**
 * Returns some random date in the range of 2021-01-01 to 2021-01-31
 */
const randomDate = () => {
  const max = 31;
  const min = 1;
  let day = Math.floor(Math.random() * max) + min;

  // We want some leading '0' for our day section.
  if (day.toString().length === 1) {
    day = `0${day}`;
  }

  return `2021-01-${day}`;
}

/**
 * Returns some random browser
 */
const randombrowser = () => {
  // Some browsers are mentioned multiple times.
  // The reason for this is to introduce some weighting.
  // => e.g. 'Chrome' will be returned more often than 'Safari'
  const browsers = ['Chrome', 'Chrome', 'Chrome', 'Edge', 'Edge', 'Firefox', 'Safari'];
  const randomIdx = Math.floor(Math.random() * browsers.length);
  const browser = browsers[randomIdx];

  return browser;
}

// -- Set these variables to your needs
// The total entries of the resulting CSV file
const totalEntries = 50000;
// ---------------------------

const data = [];

const csvWriter = createCsvWriter({
  path: 'dump.csv',
  header: [
    { id: 'date', title: 'date' },
    { id: 'browser', title: 'browser' },
  ]
});

for (let i = 0; i < totalEntries; i++) {
  data.push({
    date: format(randomDate()),
    browser: randombrowser()
  })
}

csvWriter
  .writeRecords(data)
  .then(() => console.log('The CSV file was written successfully'));