// Ratio of Obese (BMI >= 30) in U.S. Adults, CDC 2008

var data = [

  , .187, .198, , .133, .175, .151, , .1, .125, .171, , .172, .133, , .108,

  .142, .167, .201, .175, .159, .169, .177, .141, .163, .117, .182, .153, .195,

  .189, .134, .163, .133, .151, .145, .13, .139, .169, .164, .175, .135, .152,

  .169, , .132, .167, .139, .184, .159, .14, .146, .157, , .139, .183, .16, .143

];

var color = d3.scale.linear()

    .domain([d3.min(data), d3.max(data)])

    .range(["#aad", "#556"]); 

var force = d3.layout.force()

    .charge(0)

    .gravity(0)

    .size([960, 500]);

var svg = d3.select("#chart").append("svg:svg")

    .attr("width", 960 + 100)

    .attr("height", 500 + 100)

  .append("svg:g")

    .attr("transform", "translate(50,50)");

d3.json("../data/us-state-centroids.json", function(states) {

  var project = d3.geo.albersUsa(),

      idToNode = {},

      links = [],

      nodes = states.features.map(function(d) {

    var xy = project(d.geometry.coordinates);

    return idToNode[d.id] = {

      x: xy[0],

      y: xy[1],

      gravity: {x: xy[0], y: xy[1]},

      r: Math.sqrt(data[+d.id] * 5000),

      value: data[+d.id]

    };

  });

  force

      .nodes(nodes)

      .links(links)

      .start()

      .on("tick", function(e) {

    var k = e.alpha,

        kg = k * .02;

    nodes.forEach(function(a, i) {

      // Apply gravity forces.

      a.x += (a.gravity.x - a.x) * kg;

      a.y += (a.gravity.y - a.y) * kg;

      nodes.slice(i + 1).forEach(function(b) {

        // Check for collisions.

        var dx = a.x - b.x,

            dy = a.y - b.y,

            l = Math.sqrt(dx * dx + dy * dy),

            d = a.r + b.r;

        if (l < d) {

          l = (l - d) / l * k;

          dx *= l;

          dy *= l;

          a.x -= dx;

          a.y -= dy;

          b.x += dx;

          b.y += dy;

        }

      });

    });

    svg.selectAll("circle")

        .attr("cx", function(d) { return d.x; })

        .attr("cy", function(d) { return d.y; });

  });

  svg.selectAll("circle")

      .data(nodes)

    .enter().append("svg:circle")

      .style("fill", function(d) { return color(d.value); })

      .attr("cx", function(d) { return d.x; })

      .attr("cy", function(d) { return d.y; })

      .attr("r", function(d, i) { return d.r; });

});