his script is the raffle for 20 scholarships to my Engineering Management course based on this tweet https://twitter.com/buritica/status/1235268210863345664 */

rifa-platzi.js

/**
 * This script is the raffle for 20 scholarships to my Engineering Management course
 * based on this tweet https://twitter.com/buritica/status/1235268210863345664
 */

let participants = []

// get all the replies to the tweet
let questions = document.querySelectorAll('article')

/**
 * This function evaluates if there is a twitter user in the text
 * and it adds it to the list of participants as long as it's not
 * buritica, platzi or celis
 * @param {[type]} span [description]
 */
function addToRaffle (span) {
  let participant = span.innerText

  if (participant === '@buritica' || participant === '@platzi' || participant === '@CelisMX') {
    return false
  }

  if (participant.indexOf('@') === 0) {
    participants.push(participant)
  }
}

/**
 * check if the value is unique in an array
 */
function onlyUnique (value, index, self) {
  return self.indexOf(value) === index
}

/**
 * Shuffle an array from 
 * https://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array
 */
function shuffle (array) {
  let currentIndex = array.length, temporaryValue, randomIndex

  // While there remain elements to shuffle...
  while (0 !== currentIndex) {

    // Pick a remaining element...
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex -= 1;

    // And swap it with the current element.
    temporaryValue = array[currentIndex];
    array[currentIndex] = array[randomIndex];
    array[randomIndex] = temporaryValue;
  }

  return array;
}

console.log('procesando %s preguntas', questions.length)
// we iterate over the list of questions and look for all the spans
// because twitter html is unintelligible
// and then we take those spans and try to find users to add to the raffle
questions.forEach(question => {
  let spans = question.querySelectorAll('span')
  spans.forEach(addToRaffle)
})

console.log('tenemos %s usuarios', participants.length)

// we now make sure that the list of raffle participants has no duplicates
participants = participants.filter(onlyUnique)

console.log('tenemos %s usuarios unicos', participants.length)
// we shuffle the list of participants a couple times to make the raffle fair
participants = shuffle(participants)
participants = shuffle(participants)
participants = shuffle(participants)

// we pick 20 users
participants.length = 20

// we write the 20 lucky winners

console.log('los %s ganadores son %s', participants.length, participants.join(', '))