var width = 960,
    height = 500;

var color = d3.scale.category20();

var force = d3.layout.force()
    .charge(-100)
    .linkDistance(5)
    .size([width, height]);

var svg = d3.select("#chart").append("svg")
    .attr("width", width)
    .attr("height", height);

var tooltip = svg.append("text")
    .attr('dy', '15px')
    .attr('dx', '10px')
    .attr('class', 'tooltip');

d3.json("songs.json", function(songs) {
  var json = {};
  json.nodes = [];
  var ids = {};
  var radius = {};
  for (var i = 0; i < songs.length; i++) {
    radius[songs[i].id] = 0;
  }
  for (var i = 0; i < songs.length; i++) {
    radius[songs[i].id] += 1;
    if (!ids.hasOwnProperty(songs[i].id)) {
      json.nodes.push(songs[i]);
      ids[songs[i].id] = json.nodes.length - 1;
    }
  }

  json.links = [];

  for (var i = 0; i < songs.length - 1; i++) {
      json.links.push({
          source: ids[songs[i].id],
          target: ids[songs[i + 1].id]
      });
  }

  force
      .nodes(json.nodes)
      .links(json.links)
      .start();

  var link = svg.selectAll("line.link")
      .data(json.links)
      .enter().append("line")
      .attr("class", "link")
      .style("stroke-width", function(d) { return Math.sqrt(d.value); });

  var node = svg.selectAll("circle.node")
      .data(json.nodes)
      .enter().append("circle")
      .attr("class", "node")
      .call(force.drag)
      .attr("r", function(d) {
	return (2.5 + radius[d.id]);
      })
      .style("fill", function(d) {
	return color(d.artist);
      })
      .on('mouseover', function(d) {
          tooltip.text(d.artist + ' - ' + d.name);
      })
      .on('mouseout', function(d) {
          tooltip.text('');
      });

  node.append("title")
      .text(function(d) { 
	return new Date(d.date * 1000);
      });

  force.on("tick", function() {
    link.attr("x1", function(d) { return d.source.x; })
        .attr("y1", function(d) { return d.source.y; })
        .attr("x2", function(d) { return d.target.x; })
        .attr("y2", function(d) { return d.target.y; });

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