;(function() {
  d3.fisheye = {
    scale: function(scaleType) {
      return d3_fisheye_scale(scaleType(), 3, 0)
    },
    circular: function() {
      var radius = 200,
        distortion = 2,
        k0,
        k1,
        focus = [0, 0]

      function fisheye(d) {
        var dx = d.x - focus[0],
          dy = d.y - focus[1],
          dd = Math.sqrt(dx * dx + dy * dy)
        if (!dd || dd >= radius) return { x: d.x, y: d.y, z: 1 }
        var k = ((k0 * (1 - Math.exp(-dd * k1))) / dd) * 0.75 + 0.25
        return {
          x: focus[0] + dx * k,
          y: focus[1] + dy * k,
          z: Math.min(k, 10),
        }
      }

      function rescale() {
        k0 = Math.exp(distortion)
        k0 = (k0 / (k0 - 1)) * radius
        k1 = distortion / radius
        return fisheye
      }

      fisheye.radius = function(_) {
        if (!arguments.length) return radius
        radius = +_
        return rescale()
      }

      fisheye.distortion = function(_) {
        if (!arguments.length) return distortion
        distortion = +_
        return rescale()
      }

      fisheye.focus = function(_) {
        if (!arguments.length) return focus
        focus = _
        return fisheye
      }

      return rescale()
    },
  }

  function d3_fisheye_scale(scale, d, a) {
    function fisheye(_) {
      var x = scale(_),
        left = x < a,
        range = d3.extent(scale.range()),
        min = range[0],
        max = range[1],
        m = left ? a - min : max - a
      if (m == 0) m = max - min
      return ((left ? -1 : 1) * m * (d + 1)) / (d + m / Math.abs(x - a)) + a
    }

    fisheye.distortion = function(_) {
      if (!arguments.length) return d
      d = +_
      return fisheye
    }

    fisheye.focus = function(_) {
      if (!arguments.length) return a
      a = +_
      return fisheye
    }

    fisheye.copy = function() {
      return d3_fisheye_scale(scale.copy(), d, a)
    }

    fisheye.nice = scale.nice
    fisheye.ticks = scale.ticks
    fisheye.tickFormat = scale.tickFormat
    return d3.rebind(fisheye, scale, 'domain', 'range')
  }
})()