BusFactor experiments

index.js

//const fetch = require('node-fetch');
const _ = require('lodash');
const moment = require('moment');
const process = require('process');
const d3 = require('d3');

Object.prototype.inspect = function(fn = (x => x)) { console.log(fn(this)); return this; };

const repos = [
  'clojure/clojurescript',
  'facebook/react',
  'Homebrew/homebrew',
  'torvalds/linux',
];

repos.map(fetchContributors).forEach(fetchedRepo => {
  fetchedRepo.then((list) => {
    busFactor(list);
    const graphData = list.map((e, i) => ({y: e.percentNorm, x: i, user: e.login}) )
	  drawRepoGraph(graphData, list.name)
	});
});

function userRepoContributions(user) {
  // deletions are more valuable, because they imply refactorings and/or
  // better understanding of the codebase
  return user.weeks.reduce((accu, n) => {
    const timestamp = parseInt(n.w);
    const week = moment.unix(timestamp);
    const reference = moment().subtract(1, 'year');
    const diff = moment.duration(week.diff(reference)).months();
    const coeff = diff < 1 ? 0.5 : Math.exp(diff / 4);
    return accu + (n.a + n.c + n.d * 2) * coeff;
  }, 0);
}

function fetchContributors(repo) {
  const url = `https://api.github.com/repos/${repo}/stats/contributors`;

  return fetch(url)
    .then((res) => res.json())
    .then((json) => {
      const stats = json.map((user) => ({
        login: user.author.login,
        contributions: userRepoContributions(user)
      }));
      const sorted = _.sortBy(stats, 'contributions');
      const sum = _.sum(sorted.map(x => x.contributions));
      const biggest = _.reverse(_.takeRight(sorted, 10));
      const list = biggest.map(x => {
        x.percent = (x.contributions * 100.0 / sum).toFixed(2);
        return x;
      })

      const norm = _.sum(list.map(e => parseInt(e.percent)));
      list.forEach(e => { e.percentNorm = e.percent / norm * 100 }); // yeah, mutating in-place
  		list.name = repo;
  		return list;
    });
}

function busFactor(list) {
  average(list.map(e => e.percentNorm)).inspect(x => `Avg: ${x}`);
  let std = standardDeviation(list.map(e => e.percentNorm)).inspect(x => `StdDev: ${x}`);
  return (std * ((list.length - 1) / list.length)).inspect(x => `${x}`);
}

function standardDeviation(values){
  var avg = average(values);
  
  var squareDiffs = values.map(function(value){
    var diff = value - avg;
    var sqrDiff = Math.pow(diff, 2);
    return sqrDiff;
  });
  
  var avgSquareDiff = average(squareDiffs);

  return Math.sqrt(avgSquareDiff);
}

function average(data){
  return _.sum(data) / data.length;
}

function drawRepoGraph(data, name) {
  var margin = {top: 40, right: 50, bottom: 100, left: 30};
  var width = 200 - margin.left - margin.right;
  var height = 200 - margin.top - margin.bottom;

  var x = d3.scale.linear()
      .domain([d3.min(data, d => d.x), d3.max(data, d => d.x)])
      .range([0, width]);

  var y = d3.scale.linear()
      .domain([d3.min(data, d => d.y), d3.max(data, d => d.y)])
      .range([height, 0]);

  var xAxis = d3.svg.axis()
      .scale(x)
      .orient("bottom");

  var svg = d3.select("body")
    .append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
    .append("g")
      .attr("transform", `translate(${margin.left}, ${margin.top})`);

  var bar = svg.selectAll(".bar")
      .data(data)
    .enter().append("g")
      .style("fill", "#B4B4D6")
      .attr("transform", d => `translate(${x(d.x)}, ${y(d.y)})`);

  bar.append("rect")
      .attr("x", 1)
      .attr("width", width/15)
      .attr("height", d => height - y(d.y));
/*
  bar.append("text")
      .attr("y", -10)
      .attr("x", 20)
      .attr("text-anchor", "middle")
      .text(d => d3.format(",.2f")(d.y));

  bar.append("text")
		  .attr("transform", d => `translate(${0}, ${height - y(d.y) + 20}) rotate(90)`)
      .attr("dx", -10)
      .attr("dy", -15)
      .style("text-anchor", "start")
      .text(d => d.user);
*/
	svg.append("text")
  	.text(name)
  	.attr("x", 10)
  	.attr("y", 10)
    .style("text-anchor", "start")
    .style("fill", "#7A7A94")
    .style("font-family", "sans-serif");
}