d3.json('/data/bvg-graph.json', function(json){

    var width = 740,
        height = 600;

    var svg = d3.select('svg')
        .style("display", "block")
        .attr('width', width)
        .attr('height', height);

    // draw the graph edges
    var link = svg.selectAll("line.link")
      .data(json.links)
      .enter().append("line")
        .style('stroke','black');

    // draw the graph nodes
    var node = svg.selectAll("circle.node")
      .data(json.nodes)
      .enter()
      .append("circle")
        .attr("class", "node")
        .style("fill",function(d) {
            // custom colours based on train type
            if (d.name.match(/^S\+U/)) {
                return 'rgb(215,49,58)';
            }
            else if (d.name.match(/^U/)) {
                return 'rgb(0,114,171)';
            }
            else {
                return 'green';
            }
        })
        .attr("r", 12);

    var nodename = svg.selectAll("text.nodename")
      .data(json.nodes)
      .enter()
      .append("text")
      .text(function(d) {return d.name});

    // create the layout
    var force = d3.layout.force()
        .charge(-250)
        .linkDistance(function(d,e) {
          var distance = 1.5*parseFloat(d.distance)/10 - 5;
          return (isNaN(distance)) ? 10 : distance; })
        .size([width, height])
        .nodes(json.nodes)
        .links(json.links)
        .start();


    // define what to do one each tick of the animation
    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; });

        nodename.attr("x", function(d) { return d.x - 3; })
            .attr("y", function(d) { return d.y + 4; });
        });

    // precalculate force layout ticks for more natural appearance
    var k = 0;
    while ((force.alpha() > 1e-2) && (k < 40)) {
        force.tick(),
        k = k + 1;
    }
    // bind the drag interaction to the nodes
    node.call(force.drag);

    // misc stuff for auto resizing svg
    function updateWindow(){
        $("svg").width($(".site").width());
    }
    window.onresize = updateWindow;

    if ($(".site").width() < 740) {
      updateWindow();
    }

});