function o (e, t, n) {
  return e > t - n && e < t + n
}

function a (e, t) {
  return o(e, 0, t)
}

export function Spring (e, t, n) {
  this._m = e
  this._k = t
  this._c = n
  this._solution = null
  this._endPosition = 0
  this._startTime = 0
}

Spring.prototype._solve = function (e, t) {
  var n = this._c
  var i = this._m
  var r = this._k
  var o = n * n - 4 * i * r
  if (o === 0) {
    let a = -n / (2 * i)
    let s = e
    let l = t / (a * e)
    return {
      x: function (e) {
        return (s + l * e) * Math.pow(Math.E, a * e)
      },
      dx: function (e) {
        var t = Math.pow(Math.E, a * e)
        return a * (s + l * e) * t + l * t
      }
    }
  }
  if (o > 0) {
    let c = (-n - Math.sqrt(o)) / (2 * i)
    let u = (-n + Math.sqrt(o)) / (2 * i)
    let l = (t - c * e) / (u - c)
    let s = e - l
    return {
      x: function (e) {
        let t
        let n
        if (e === this._t) {
          t = this._powER1T
          n = this._powER2T
        }
        this._t = e
        if (!t) {
          t = this._powER1T = Math.pow(Math.E, c * e)
        }
        if (!n) {
          n = this._powER2T = Math.pow(Math.E, u * e)
        }
        return s * t + l * n
      },
      dx: function (e) {
        let t
        let n
        if (e === this._t) {
          t = this._powER1T
          n = this._powER2T
        }
        this._t = e
        if (!t) {
          t = this._powER1T = Math.pow(Math.E, c * e)
        }
        if (!n) {
          n = this._powER2T = Math.pow(Math.E, u * e)
        }
        return s * c * t + l * u * n
      }
    }
  }
  var d = Math.sqrt(4 * i * r - n * n) / (2 * i)

  var a = -n / 2 * i

  var s = e

  var l = (t - a * e) / d
  return {
    x: function (e) {
      return Math.pow(Math.E, a * e) * (s * Math.cos(d * e) + l * Math.sin(d * e))
    },
    dx: function (e) {
      var t = Math.pow(Math.E, a * e)

      var n = Math.cos(d * e)

      var i = Math.sin(d * e)
      return t * (l * d * n - s * d * i) + a * t * (l * i + s * n)
    }
  }
}
Spring.prototype.x = function (e) {
  if (e === undefined) {
    e = ((new Date()).getTime() - this._startTime) / 1e3
  }
  return this._solution ? this._endPosition + this._solution.x(e) : 0
}
Spring.prototype.dx = function (e) {
  if (e === undefined) {
    e = ((new Date()).getTime() - this._startTime) / 1e3
  }
  return this._solution ? this._solution.dx(e) : 0
}
Spring.prototype.setEnd = function (e, t, n) {
  if (!n) {
    n = (new Date()).getTime()
  }
  if (e !== this._endPosition || !a(t, 0.4)) {
    t = t || 0
    var i = this._endPosition
    if (this._solution) {
      if (a(t, 0.4)) {
        t = this._solution.dx((n - this._startTime) / 1e3)
      }
      i = this._solution.x((n - this._startTime) / 1e3)
      if (a(t, 0.4)) {
        t = 0
      }
      if (a(i, 0.4)) {
        i = 0
      }
      i += this._endPosition
    }
    if (!(this._solution && a(i - e, 0.4) && a(t, 0.4))) {
      this._endPosition = e
      this._solution = this._solve(i - this._endPosition, t)
      this._startTime = n
    }
  }
}
Spring.prototype.snap = function (e) {
  this._startTime = (new Date()).getTime()
  this._endPosition = e
  this._solution = {
    x: function () {
      return 0
    },
    dx: function () {
      return 0
    }
  }
}
Spring.prototype.done = function (e) {
  if (!e) {
    e = (new Date()).getTime()
  }
  return o(this.x(), this._endPosition, 0.4) && a(this.dx(), 0.4)
}
Spring.prototype.reconfigure = function (e, t, n) {
  this._m = e
  this._k = t
  this._c = n
  if (!this.done()) {
    this._solution = this._solve(this.x() - this._endPosition, this.dx())
    this._startTime = (new Date()).getTime()
  }
}
Spring.prototype.springConstant = function () {
  return this._k
}
Spring.prototype.damping = function () {
  return this._c
}
Spring.prototype.configuration = function () {
  function e (e, t) {
    e.reconfigure(1, t, e.damping())
  }

  function t (e, t) {
    e.reconfigure(1, e.springConstant(), t)
  }
  return [{
    label: 'Spring Constant',
    read: this.springConstant.bind(this),
    write: e.bind(this, this),
    min: 100,
    max: 1e3
  }, {
    label: 'Damping',
    read: this.damping.bind(this),
    write: t.bind(this, this),
    min: 1,
    max: 500
  }]
}