(function() {
  var COILS, D, HEIGHT, SAMPLES, THETA, WIDTH, a, b, line_generator, number_of_points, points, radius, randint, s, spiral, svg, svg_s;

  randint = function(n) {
    return Math.round(Math.random() * n);
  };

  a = 0;

  D = 8 + randint(16);

  b = D / (2 * Math.PI);

  COILS = 2 + randint(6);

  THETA = 2 * Math.PI * COILS;

  SAMPLES = 48;

  number_of_points = Math.ceil(THETA / (2 * Math.PI) * SAMPLES) + 1;

  points = d3.range(0, number_of_points).map(function(i) {
    var theta;

    theta = i * 2 * Math.PI / SAMPLES;
    return {
      theta: theta - Math.PI / 2,
      r: a + b * theta
    };
  });

  WIDTH = 960;

  HEIGHT = 500;

  svg = d3.select('body').append('svg').attr({
    width: WIDTH,
    height: HEIGHT
  }).append('g').attr({
    transform: "translate(" + (WIDTH / 2) + "," + (HEIGHT / 2) + ")"
  });

  radius = a + b * THETA;

  svg.append('circle').attr({
    "class": 'radius_indicator',
    r: radius
  });

  svg.append('line').attr({
    "class": 'axis',
    x1: -WIDTH,
    x2: WIDTH
  });

  svg.append('line').attr({
    "class": 'axis',
    y1: -HEIGHT,
    y2: HEIGHT
  });

  line_generator = d3.svg.line().x(function(d) {
    return d.r * Math.cos(d.theta);
  }).y(function(d) {
    return d.r * Math.sin(d.theta);
  }).interpolate('linear');

  spiral = svg.append('path').datum(points).attr({
    "class": 'spiral',
    d: line_generator
  });

  s = Math.PI * D * COILS * COILS;

  svg_s = spiral[0][0].getTotalLength();

  svg.append('text').text("a = " + a).attr({
    "class": 'label',
    x: -WIDTH / 2 + 20,
    y: -HEIGHT / 2 + 20,
    dy: '0.35em'
  });

  svg.append('text').text("b ≈ " + (d3.format('.3f')(b))).attr({
    "class": 'label',
    x: -WIDTH / 2 + 20,
    y: -HEIGHT / 2 + 45,
    dy: '0.35em'
  });

  svg.append('text').text("D = 2πb =  " + D).attr({
    "class": 'label',
    x: -WIDTH / 2 + 20,
    y: +HEIGHT / 2 - 45,
    dy: '0.35em'
  });

  svg.append('text').text("n = " + COILS).attr({
    "class": 'label',
    x: -WIDTH / 2 + 20,
    y: +HEIGHT / 2 - 20,
    dy: '0.35em'
  });

  svg.append('text').text("r ≈ " + (d3.format('.0f')(radius))).attr({
    "class": 'label',
    x: radius + 10,
    dy: '-0.25em'
  });

  svg.append('text').text("s ≈ " + (d3.format(',.0f')(s))).style({
    fill: 'black'
  }).attr({
    "class": 'label',
    x: 6,
    y: -radius,
    dy: '-0.25em'
  });

  svg.append('text').text("E ≈ " + (d3.format(',.3f')(svg_s - s))).style({
    fill: 'brown',
    'font-size': '14px'
  }).attr({
    "class": 'label',
    x: 6,
    y: -radius - 20,
    dy: '-0.25em'
  });

}).call(this);