#!/usr/bin/env node

var egg_to_embryo = 0.75;
var embryo_to_blastocyst = 0.50;
var blastocyte_chance = 0.3; // egg_to_embryo * embryo_to_blastocyst;
var debug = false;

function exponent(x, y) {
  var exp = 1;
  for (var i = 0; i < y; i++) {
    exp *= x;
  }
  return exp;
}

function factorial(n) {
  var fact = n;
  for (var i = n - 1; i > 0; i--) {
    fact *= i;
  }
  return fact;
}

function nCr(n, r) {
  if (r == 0 || r == n) { return 1; }
  return factorial(n) / (factorial(n - r) * factorial(r));
}

function chance(pBlastocyte, eggs, blastocytes) {
  var success = exponent(pBlastocyte, blastocytes);
  var failure = exponent(1 - pBlastocyte, eggs - blastocytes);
  var chance = success * failure;
  var ways = nCr(eggs, blastocytes);
  var probability = chance * ways;
  if (debug) {
    console.log(eggs + ' eggs in, ' + blastocytes + ' blastocytes out');
    console.log('  success: ' + success);
    console.log('  failure: ' + failure);
    console.log('  chance: ' + chance);
    console.log('  ways: ' + ways);
    console.log('  probability: ' + probability);
  }
  return (exponent(pBlastocyte, blastocytes)
    * exponent(1 - pBlastocyte, eggs - blastocytes))
      * nCr(eggs, blastocytes);
}

for (var eggs = 1; eggs <= 20; eggs++) {
  var sum = 0;
  for (var blastocytes = eggs; blastocytes >= 0; blastocytes--) {
    var prob = chance(blastocyte_chance, eggs, blastocytes);
    sum += prob;
    console.log(eggs + ' eggs in, ' + blastocytes + ' blastocytes out');
    console.log('  probability (exactly ' + blastocytes + '): ' + Math.round(prob * 100) + '%');
    console.log('  cumulative probability (at least ' + blastocytes + '): ' + Math.round(sum * 100) + '%');
  }
  console.log();
}