SITCON 2019 Bingo Card proof-of-concept

bingo-pos.js

crypto = require('crypto')

const sponsors = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', '+']

const communities = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']

// 5x5 grid; 0: sponsor; 1: community
const patterns = [0b0010001010100010101000100, 0b1010001010000010101010000, 
                  0b1000100100010100010010001, 0b0010010001010101000100100]

function md5Hash(token) {
  var md5 = crypto.createHash('md5')
  md5.update(token)
  return md5.digest('hex')
}

function hex2Dec(s, i) {
  var c = s.charCodeAt(i)
  return c > 0x60 ? (c - 0x57) : (c - 0x30)
}

function swap(arr, a, b) {
  var _ = arr[a]
  arr[a] = arr[b]
  arr[b] = _
}

function generateBingo(token) {
  var hash = md5Hash(token)
  
  var shuffled_sponsors = [...sponsors]
  for (i = 0; i < 16; i++)
    swap(shuffled_sponsors, hex2Dec(hash, i), 15)
  
  var shuffled_communities = [...communities]
  for (i = 0; i < 8; i++)
    swap(shuffled_communities, hex2Dec(hash, 16+i) % 8, 7)
  
  // generate bingo card using predefined pattern
  var grid = new Array(25)
  var pattern = patterns[hex2Dec(hash, 24) % 4]
  for (var i = 0; i < 25; i++)
    if ((pattern >> i) & 1)
      grid[i] = { 'type': 'community', 'name': shuffled_communities.shift() }
  
  // free space in the middle
  grid[12] = { 'type': 'free_space' }

  // fill the remaining with sponsors
  for (var i = 0; i < 25; i++)
    if (!grid[i])
      grid[i] = { 'type': 'sponsor', 'name': shuffled_sponsors.shift() }
  
  return grid
}

// Example code
// Usage: node bingo-pos.js [token]
var bingoGrid = generateBingo(process.argv[2] || '我能吞下玻璃而不傷身體')
console.log(bingoGrid)

var str = '='.repeat(21) + '\n'
for (var y = 0; y < 5; y++) {
  for (var x = 0; x < 5; x++) {
  	var i = bingoGrid[y * 5 + x]
  	str += `| ${i.name || '@'}${i.type == 'community' ? '*' : ' '}`
  } 
  str += '|\n'
}
str += '='.repeat(21)
console.log(str)