// Inspired by Lee Byron's test data generator.
function bumpLayer(n, o) {

  function bump(a) {
    var x = 1 / (.1 + Math.random()),
        y = 2 * Math.random() - .5,
        z = 10 / (.1 + Math.random());
    for (var i = 0; i < n; i++) {
      var w = (i / n - y) * z;
      a[i] += x * Math.exp(-w * w);
    }
  }

  var a = [], i;
  for (i = 0; i < n; ++i) a[i] = o + o * Math.random();
  for (i = 0; i < 5; ++i) bump(a);
  return a.map(function(d, i) { return {x: i, y: d, w: Math.random()*100}; });
}

var n = 4, // number of layers
    m = 5, // number of samples per layer
    stack = d3.layout.stack(),
    layers = stack(d3.range(n).map(function() { return bumpLayer(m, .1); })),
    yGroupMax = d3.max(layers, function(layer) { return d3.max(layer, function(d) { return d.y; }); }),
    yStackMax = d3.max(layers, function(layer) { return d3.max(layer, function(d) { return d.y0 + d.y; }); }),
    wGroupMax = d3.max(layers, function(layer) { return d3.max(layer, function(d) { return d.w; })});

var margin = {top: 40, right: 10, bottom: 20, left: 10},
    width = 600 - margin.left - margin.right,
    height = 600 - margin.top - margin.bottom;

var x = d3.scale.ordinal()
    .domain(d3.range(m))
    .rangeRoundBands([0, width], .08);

var y = d3.scale.linear()
    .domain([0, yStackMax])
    .range([height, 0]);

var color = d3.scale.category10()
    .domain(d3.range(n - 1))
    .range(["#EA8825", "#FCBC6E", "#FF5800", "#F58025"])

var xAxis = d3.svg.axis()
    .scale(x)
    .tickSize(0)
    .tickPadding(6)
    .orient("bottom");

var svg = d3.select("#chart").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 layer = svg.selectAll(".layer")
    .data(layers)
  .enter().append("g")
    .attr("class", "layer")
    .style("fill", function(d, i) { return color(i); });

var rect = layer.selectAll("rect")
    .data(function(d) { return d; })
  .enter().append("rect")
    .attr("x", function(d) { return x(d.x) + (x.rangeBand() * (1 - d.w / wGroupMax)) / 2; })
    // .attr("x", function(d) { return x(d.x); })
    .attr("y", height)
    .attr("width", function(d) { return x.rangeBand() * d.w / wGroupMax; })
    .attr("height", 0);

rect.transition()
    .delay(function(d, i) { return i * 10; })
    .attr("y", function(d) { return y(d.y0 + d.y); })
    .attr("height", function(d) { return y(d.y0) - y(d.y0 + d.y); });

svg.append("g")
    .attr("class", "x axis")
    .attr("transform", "translate(0," + height + ")")
    .call(xAxis);