InterpolatedCurve

package com.hypixel.hytale.builtin.hytalegenerator.framework.math;

import it.unimi.dsi.fastutil.doubles.Double2DoubleFunction;
import javax.annotation.Nonnull;

public class InterpolatedCurve implements Double2DoubleFunction {
   @Nonnull
   private final Double2DoubleFunction functionA;
   @Nonnull
   private final Double2DoubleFunction functionB;
   private final double positionA;
   private final double positionB;
   private final double distance;
   private final double smoothTransition;

   public InterpolatedCurve(
      double positionA, double positionB, double smoothTransition, @Nonnull Double2DoubleFunction functionA, @Nonnull Double2DoubleFunction functionB
   ) {
      if (!(smoothTransition < 0.0) && !(smoothTransition > 1.0)) {
         this.smoothTransition = smoothTransition;
         this.positionA = Math.min(positionA, positionB);
         this.positionB = Math.max(positionA, positionB);
         this.distance = positionB - positionA;
         this.functionA = functionA;
         this.functionB = functionB;
      } else {
         throw new IllegalArgumentException();
      }
   }

   public double get(double x) {
      if (x < this.positionA) {
         return this.functionA.get(x);
      } else if (x > this.positionB) {
         return this.functionB.get(x);
      } else if (this.distance == 0.0) {
         return (this.functionA.get(x) + this.functionB.get(x)) * 0.5;
      } else {
         double bRatio = this.transitionCurve((x - this.positionA) / this.distance);
         double aRatio = 1.0 - bRatio;
         return aRatio * this.functionA.get(x) + bRatio * this.functionB.get(x);
      }
   }

   public double transitionCurve(double ratio) {
      double a = ratio * 3.141592653589793;
      double v = Math.cos(a);
      v++;
      v /= 2.0;
      v = 1.0 - v;
      return v * this.smoothTransition + ratio * (1.0 - this.smoothTransition);
   }
}