var NODE_RADIUS = 7;
var GATE_RADIUS = 2;
var REPEL_FORCE = 0;
var LINK_DISTANCE = 100;

var WIDTH = 1000;
var HEIGHT = 500;

function drawGraph (graph, panel) {
  var d3cola = cola.d3adaptor()
    .avoidOverlaps(true)
    .size([WIDTH, HEIGHT]);

  var svg = d3.select(panel);

  d3.selectAll(panel + '> *').remove();

  // define arrow markers for graph links
  svg.append('svg:defs').append('svg:marker')
    .attr('id', 'end-arrow')
    .attr('viewBox', '0 -5 10 10')
    .attr('refX', 6)
    .attr('markerWidth', 4)
    .attr('markerHeight', 4)
    .attr('orient', 'auto')
    .append('svg:path')
    .attr('d', 'M0,-5L10,0L0,5');

  graph.nodes.forEach(function (v) {
    v.height = v.width = 2 * (v.name === 'GATE' ? GATE_RADIUS : NODE_RADIUS);
  });

  d3cola
    .nodes(graph.nodes)
    .links(graph.links)
    .constraints(graph.constraints)
    .symmetricDiffLinkLengths(REPEL_FORCE)
    .linkDistance(LINK_DISTANCE)
    .start(10, 15, 20);

  var path = svg.selectAll('.link')
    .data(graph.links)
    .enter().append('svg:path')
    .attr('class', 'link');

  path.append('title')
    .text(function (d) {
      var text = '';
      text += 'Weight: ' + Math.round(d.weight * 1000) / 1000 + '\n';
      text += 'Source: ' + d.source.id + '\n';
      text += 'Target: ' + d.target.id;
      return text;
    });

  var node = svg.selectAll('.node')
    .data(graph.nodes)
    .enter().append('circle')
    .attr('class', function (d) {
      return 'node ' + d.name;
    })
    .attr('r', function (d) {
      return d.name === 'GATE' ? GATE_RADIUS : NODE_RADIUS;
    })

  .call(d3cola.drag);

  node.append('title')
    .text(function (d) {
      var text = '';
      text += 'Activation: ' + Math.round(d.activation * 1000) / 1000 + '\n';
      text += 'Bias: ' + Math.round(d.bias * 1000) / 1000 + '\n';
      text += 'Position: ' + d.id;
      return text;
    });

  var label = svg.selectAll('.label')
    .data(graph.nodes)
    .enter().append('text')
    .attr('class', 'label')
    .text(function (d) {
      return '(' + d.index + ') ' + d.name;
    })
    .call(d3cola.drag);

  d3cola.on('tick', function () {
    // draw directed edges with proper padding from node centers
    path.attr('d', function (d) {
      var deltaX = d.target.x - d.source.x;
      var deltaY = d.target.y - d.source.y;
      var dist = Math.sqrt(deltaX * deltaX + deltaY * deltaY);
      var normX = deltaX / dist;
      var normY = deltaY / dist;

      if (isNaN(normX)) normX = 0;
      if (isNaN(normY)) normY = 0;

      var sourcePadding = d.source.width / 2;
      var targetPadding = d.target.width / 2 + 2;
      var sourceX = d.source.x + (sourcePadding * normX);
      var sourceY = d.source.y + (sourcePadding * normY);
      var targetX = d.target.x - (targetPadding * normX);
      var targetY = d.target.y - (targetPadding * normY);

      // Defaults for normal edge.
      var drx = 0;
      var dry = 0;
      var xRotation = 0; // degrees
      var largeArc = 0; // 1 or 0
      var sweep = 1; // 1 or 0

      // Self edge.
      if (d.source.x === d.target.x && d.source.y === d.target.y) {
        xRotation = -45;
        largeArc = 1;
        drx = 20;
        dry = 20;
        targetX = targetX + 1;
        targetY = targetY + 1;
      }
      return 'M' + sourceX + ',' + sourceY + 'A' + drx + ',' + dry + ' ' + xRotation + ',' + largeArc + ',' + sweep + ' ' + targetX + ',' + targetY;
    });

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

    label
      .attr('x', function (d) {
        return d.x + 10;
      })
      .attr('y', function (d) {
        return d.y - 10;
      });
  });
}