MultiMixDensity

package com.hypixel.hytale.builtin.hytalegenerator.density.nodes;

import com.hypixel.hytale.builtin.hytalegenerator.ArrayUtil;
import com.hypixel.hytale.builtin.hytalegenerator.density.Density;
import com.hypixel.hytale.builtin.hytalegenerator.framework.math.Interpolation;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.function.BiFunction;
import javax.annotation.Nonnull;

public class MultiMixDensity extends Density {
   @Nonnull
   private final List<MultiMixDensity.Segment> segments;
   private final double min;
   private final double max;
   private final Density firstDensity;
   private final Density lastDensity;
   private Density influenceDensity;

   public MultiMixDensity(@Nonnull List<MultiMixDensity.Key> keys, @Nonnull Density influenceDensity) {
      if (keys.size() < 2) {
         throw new IllegalArgumentException("must have at least two keys");
      } else {
         keys.sort(Comparator.comparingDouble(element -> element.value));
         if (!isKeysUnique(keys)) {
            throw new IllegalArgumentException("Duplicate keys provided.");
         } else {
            this.segments = new ArrayList<>(keys.size() - 1);

            for (int i = 1; i < keys.size(); i++) {
               MultiMixDensity.Key key0 = keys.get(i - 1);
               MultiMixDensity.Key key1 = keys.get(i);
               this.segments.add(new MultiMixDensity.Segment(key0, key1));
            }

            this.min = keys.getFirst().value;
            this.max = keys.getLast().value;
            this.firstDensity = keys.getFirst().density;
            this.lastDensity = keys.getLast().density;
            this.influenceDensity = influenceDensity;
         }
      }
   }

   @Override
   public double process(@Nonnull Density.Context context) {
      double influence = this.influenceDensity.process(context);
      if (influence <= this.min) {
         return this.firstDensity.process(context);
      } else if (influence >= this.max) {
         return this.lastDensity.process(context);
      } else {
         int index = ArrayUtil.sortedSearch(this.segments, influence, MultiMixDensity.Segment.GaugeSegmentComparator.INSTANCE);
         if (index == -1) {
            assert false : "should never get here";

            return 0.0;
         } else {
            return this.segments.get(index).getValue(context, influence);
         }
      }
   }

   @Override
   public void setInputs(@Nonnull Density[] inputs) {
      if (inputs.length != 1) {
         throw new IllegalArgumentException("inputs.length != 1");
      } else {
         this.influenceDensity = inputs[0];
      }
   }

   public static boolean isKeysUnique(@Nonnull List<MultiMixDensity.Key> keys) {
      for (int i = 1; i < keys.size(); i++) {
         if (keys.get(i).value == keys.get(i - 1).value) {
            return false;
         }
      }

      return true;
   }

   public static record Key(double value, Density density) {
   }

   private static class Segment {
      @Nonnull
      private final MultiMixDensity.Key key0;
      @Nonnull
      private final MultiMixDensity.Key key1;
      private final double magnitude;

      public Segment(@Nonnull MultiMixDensity.Key key0, @Nonnull MultiMixDensity.Key key1) {
         assert key0.value < key1.value : "key0 should be smaller than key1";

         this.key0 = key0;
         this.key1 = key1;
         this.magnitude = key1.value - key0.value;
      }

      public boolean contains(double gauge) {
         return gauge >= this.key0.value && gauge <= this.key1.value;
      }

      public double getValue(@Nonnull Density.Context context, double gauge) {
         assert gauge >= this.key0.value && gauge <= this.key1.value : "mix outside range";

         double THRESHOLD_INPUT_0 = 0.0;
         double THRESHOLD_INPUT_1 = 1.0;
         double weight = (gauge - this.key0.value) / this.magnitude;
         if (weight == 0.0) {
            return this.key0.density.process(context);
         } else if (weight == 1.0) {
            return this.key1.density.process(context);
         } else if (this.key0.density == this.key1.density) {
            return this.key0.density.process(context);
         } else {
            double value0 = this.key0.density.process(context);
            double value1 = this.key1.density.process(context);
            return Interpolation.linear(value0, value1, weight);
         }
      }

      public static class GaugeSegmentComparator implements BiFunction<Double, MultiMixDensity.Segment, Integer> {
         public static final MultiMixDensity.Segment.GaugeSegmentComparator INSTANCE = new MultiMixDensity.Segment.GaugeSegmentComparator();

         public GaugeSegmentComparator() {
         }

         @Nonnull
         public Integer apply(Double gauge, @Nonnull MultiMixDensity.Segment segment) {
            if (gauge < segment.key0.value) {
               return -1;
            } else {
               return gauge >= segment.key1.value ? 1 : 0;
            }
         }
      }
   }
}