var m = [19, 20, 20, 19], // top right bottom left margin
    w = 960 - m[1] - m[3], // width
    h = 136 - m[0] - m[2], // height
    z = 17; // cell size

var day = d3.time.format("%w"),
    week = d3.time.format("%U"),
    format = d3.time.format("%Y-%m-%d");

var color = d3.scale.quantile()
    .range(d3.range(9).reverse());

var svg = d3.select("#chart").selectAll("svg")
    .data(d3.range(1993, 2011))
  .enter().append("svg")
    .attr("width", w + m[1] + m[3])
    .attr("height", h + m[0] + m[2])
    .attr("class", "RdYlGn")
  .append("g")
    .attr("transform", "translate(" + (m[3] + (w - z * 53) / 2) + "," + (m[0] + (h - z * 7) / 2) + ")");

svg.append("text")
    .attr("transform", "translate(-6," + z * 3.5 + ")rotate(-90)")
    .attr("text-anchor", "middle")
    .text(String);

var rect = svg.selectAll("rect.day")
    .data(function(d) { return d3.time.days(new Date(d, 0, 1), new Date(d + 1, 0, 1)); })
  .enter().append("rect")
    .attr("class", "day")
    .attr("width", z)
    .attr("height", z)
    .attr("x", function(d) { return week(d) * z; })
    .attr("y", function(d) { return day(d) * z; });

svg.selectAll("path.month")
    .data(function(d) { return d3.time.months(new Date(d, 0, 1), new Date(d + 1, 0, 1)); })
  .enter().append("path")
    .attr("class", "month")
    .attr("d", monthPath);

d3.csv("vix.csv", function(csv) {
  var data = d3.nest()
      .key(function(d) { return d.Date; })
      .rollup(function(d) { return d[0].Open; })
      .map(csv);

  color.domain(d3.values(data));

  rect
      .attr("class", function(d) { return "day q" + color(data[format(d)]) + "-9"; })
    .append("title")
      .text(function(d) { return (d = format(d)) + (d in data ? ": " + data[d] : ""); });
});

function monthPath(t0) {
  var t1 = new Date(t0.getUTCFullYear(), t0.getUTCMonth() + 1, 0),
      d0 = +day(t0), w0 = +week(t0),
      d1 = +day(t1), w1 = +week(t1);
  return "M" + (w0 + 1) * z + "," + d0 * z
      + "H" + w0 * z + "V" + 7 * z
      + "H" + w1 * z + "V" + (d1 + 1) * z
      + "H" + (w1 + 1) * z + "V" + 0
      + "H" + (w0 + 1) * z + "Z";
}
