Paper/paper-api/src/main/java/org/bukkit/Registry.java

package org.bukkit;

import com.google.common.collect.ImmutableMap;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Map;
import org.bukkit.advancement.Advancement;
import org.bukkit.block.Biome;
import org.bukkit.boss.KeyedBossBar;
import org.bukkit.enchantments.Enchantment;
import org.bukkit.entity.EntityType;
import org.bukkit.loot.LootTables;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

/**
 * Represents a registry of Bukkit objects that may be retrieved by
 * {@link NamespacedKey}.
 *
 * @param <T> type of item in the registry
 */
public interface Registry<T extends Keyed> extends Iterable<T> {

    /**
     * Server advancements.
     *
     * @see Bukkit#getAdvancement(org.bukkit.NamespacedKey)
     * @see Bukkit#advancementIterator()
     */
    Registry<Advancement> ADVANCEMENT = new Registry<Advancement>() {

        @Nullable
        @Override
        public Advancement get(@NotNull NamespacedKey key) {
            return Bukkit.getAdvancement(key);
        }

        @NotNull
        @Override
        public Iterator<Advancement> iterator() {
            return Bukkit.advancementIterator();
        }
    };
    /**
     * Server art.
     *
     * @see Art
     */
    Registry<Art> ART = new SimpleRegistry<>(Art.class);
    /**
     * Server biomes.
     *
     * @see Biome
     */
    Registry<Biome> BIOME = new SimpleRegistry<>(Biome.class);
    /**
     * Custom boss bars.
     *
     * @see Bukkit#getBossBar(org.bukkit.NamespacedKey)
     * @see Bukkit#getBossBars()
     */
    Registry<KeyedBossBar> BOSS_BARS = new Registry<KeyedBossBar>() {

        @Nullable
        @Override
        public KeyedBossBar get(@NotNull NamespacedKey key) {
            return Bukkit.getBossBar(key);
        }

        @NotNull
        @Override
        public Iterator<KeyedBossBar> iterator() {
            return Bukkit.getBossBars();
        }
    };
    /**
     * Server enchantments.
     *
     * @see Enchantment#getByKey(org.bukkit.NamespacedKey)
     */
    Registry<Enchantment> ENCHANTMENT = new Registry<Enchantment>() {

        @Nullable
        @Override
        public Enchantment get(@NotNull NamespacedKey key) {
            return Enchantment.getByKey(key);
        }

        @NotNull
        @Override
        public Iterator<Enchantment> iterator() {
            return Arrays.asList(Enchantment.values()).iterator();
        }
    };
    /**
     * Server entity types.
     *
     * @see EntityType
     */
    Registry<EntityType> ENTITY_TYPE = new SimpleRegistry<>(EntityType.class);
    /**
     * Default server loot tables.
     *
     * @see LootTables
     */
    Registry<LootTables> LOOT_TABLES = new SimpleRegistry<>(LootTables.class);
    /**
     * Server materials.
     *
     * @see Material
     */
    Registry<Material> MATERIAL = new SimpleRegistry<>(Material.class);
    /**
     * Server statistics.
     *
     * @see Statistic
     */
    Registry<Statistic> STATISTIC = new SimpleRegistry<>(Statistic.class);

    /**
     * Get the object by its key.
     *
     * @param key non-null key
     * @return item or null if does not exist
     */
    @Nullable
    T get(@NotNull NamespacedKey key);

    final static class SimpleRegistry<T extends Enum<T> & Keyed> implements Registry<T> {

        private final Map<NamespacedKey, T> map;

        protected SimpleRegistry(@NotNull Class<T> type) {
            ImmutableMap.Builder<NamespacedKey, T> builder = ImmutableMap.builder();

            for (T entry : type.getEnumConstants()) {
                builder.put(entry.getKey(), entry);
            }

            map = builder.build();
        }

        @Nullable
        @Override
        public T get(@NotNull NamespacedKey key) {
            return map.get(key);
        }

        @NotNull
        @Override
        public Iterator<T> iterator() {
            return map.values().iterator();
        }
    }
}