TieredList

package com.hypixel.hytale.builtin.hytalegenerator.datastructures;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;
import javax.annotation.Nonnull;

public class TieredList<E> {
   @Nonnull
   private final Map<Integer, ArrayList<E>> elements;
   private final int tiers;
   private List<Integer> sortedTierList;

   public TieredList() {
      this(0);
   }

   public TieredList(int tiers) {
      if (tiers < 0) {
         throw new IllegalArgumentException("negative number of tiers");
      } else {
         this.tiers = tiers;
         this.elements = new HashMap<>();

         for (int tier = 0; tier < tiers; tier++) {
            this.elements.put(tier, new ArrayList<>());
         }

         this.updateSortedTierList();
      }
   }

   @Nonnull
   public TieredList<E> addTier(int tier) {
      if (this.tierExists(tier)) {
         throw new IllegalArgumentException("tier already exists " + tier);
      } else {
         this.elements.put(tier, new ArrayList<>());
         this.updateSortedTierList();
         return this;
      }
   }

   @Nonnull
   public TieredList<E> removeTier(int tier) {
      if (!this.tierExists(tier)) {
         return this;
      } else {
         this.elements.remove(tier);
         this.updateSortedTierList();
         return this;
      }
   }

   public void add(@Nonnull E element, int tier) {
      if (element == null) {
         throw new NullPointerException();
      } else {
         if (!this.tierExists(tier)) {
            this.addTier(tier);
         }

         this.elements.get(tier).add(element);
      }
   }

   public boolean isEmpty() {
      for (List<E> list : this.elements.values()) {
         if (!list.isEmpty()) {
            return false;
         }
      }

      return true;
   }

   public E peek() {
      for (int tier = 0; tier < this.tiers; tier++) {
         List<E> tierElements = this.elements.get(tier);
         if (!tierElements.isEmpty()) {
            return tierElements.getFirst();
         }
      }

      throw new IllegalStateException("queue is empty");
   }

   public E remove() {
      for (int tier = 0; tier < this.tiers; tier++) {
         List<E> tierElements = this.elements.get(tier);
         if (!tierElements.isEmpty()) {
            return tierElements.removeFirst();
         }
      }

      throw new IllegalStateException("queue is empty");
   }

   public int size() {
      int size = 0;

      for (List<E> list : this.elements.values()) {
         size += list.size();
      }

      return size;
   }

   public int size(int tier) {
      return !this.tierExists(tier) ? 0 : this.elements.get(tier).size();
   }

   @Nonnull
   public TieredList<E> forEach(int tier, @Nonnull Consumer<? super E> consumer) {
      if (!this.tierExists(tier)) {
         return this;
      } else {
         this.elements.get(tier).forEach(consumer);
         return this;
      }
   }

   @Nonnull
   public TieredList<E> removeEach(int tier, @Nonnull Consumer<? super E> consumer) {
      if (!this.tierExists(tier)) {
         return this;
      } else {
         for (E e : this.elements.get(tier)) {
            consumer.accept(e);
         }

         new ArrayList();
         return this;
      }
   }

   @Nonnull
   public TieredList<E> forEach(@Nonnull Consumer<? super E> consumer) {
      ArrayList<Integer> tiers = new ArrayList<>(this.getTiers());
      tiers.sort(Comparator.naturalOrder());

      for (int tier : tiers) {
         this.forEach(tier, consumer);
      }

      return this;
   }

   @Nonnull
   public TieredList<E> removeEach(@Nonnull Consumer<? super E> consumer) {
      for (int tier : this.getTiers()) {
         this.removeEach(tier, consumer);
      }

      return this;
   }

   @Nonnull
   public Iterator<E> iterator(int tier) {
      if (!this.tierExists(tier)) {
         throw new IllegalArgumentException("tier doesn't exist");
      } else {
         return this.elements.get(tier).iterator();
      }
   }

   @Nonnull
   public List<E> listOf(int tier) {
      if (!this.tierExists(tier)) {
         throw new IllegalArgumentException("tier doesn't exist");
      } else {
         return Collections.unmodifiableList(this.elements.get(tier));
      }
   }

   public boolean tierExists(int tier) {
      return this.elements.containsKey(tier);
   }

   public List<Integer> getTiers() {
      return this.sortedTierList;
   }

   private void updateSortedTierList() {
      List<Integer> tierList = new ArrayList<>(this.elements.keySet());
      tierList.sort(Comparator.naturalOrder());
      tierList = Collections.unmodifiableList(tierList);
      this.sortedTierList = tierList;
   }

   @Nonnull
   @Override
   public String toString() {
      return "TieredList{elements=" + this.elements + ", tiers=" + this.tiers + ", sortedTierList=" + this.sortedTierList + "}";
   }
}