export const spline = (function() {

  class _CubicHermiteSpline {
    constructor(lerp) {
      this._points = [];
      this._lerp = lerp;
    }

    AddPoint(t, d) {
      this._points.push([t, d]);
    }

    Get(t) {
      let p1 = 0;

      for (let i = 0; i < this._points.length; i++) {
        if (this._points[i][0] >= t) {
          break;
        }
        p1 = i;
      }

      const p0 = Math.max(0, p1 - 1);
      const p2 = Math.min(this._points.length - 1, p1 + 1);
      const p3 = Math.min(this._points.length - 1, p1 + 2);

      if (p1 == p2) {
        return this._points[p1][1];
      }

      return this._lerp(
          (t - this._points[p1][0]) / (
              this._points[p2][0] - this._points[p1][0]),
          this._points[p0][1], this._points[p1][1],
          this._points[p2][1], this._points[p3][1]);
    }
  };

  class _LinearSpline {
    constructor(lerp) {
      this._points = [];
      this._lerp = lerp;
    }

    AddPoint(t, d) {
      this._points.push([t, d]);
    }

    Get(t) {
      let p1 = 0;

      for (let i = 0; i < this._points.length; i++) {
        if (this._points[i][0] >= t) {
          break;
        }
        p1 = i;
      }

      const p2 = Math.min(this._points.length - 1, p1 + 1);

      if (p1 == p2) {
        return this._points[p1][1];
      }

      return this._lerp(
          (t - this._points[p1][0]) / (
              this._points[p2][0] - this._points[p1][0]),
          this._points[p1][1], this._points[p2][1]);
    }
  }

  return {
    CubicHermiteSpline: _CubicHermiteSpline,
    LinearSpline: _LinearSpline,
  };
})();