common-utils/src/main/java/org/warp/commonutils/type/UnmodifiableSet.java

package org.warp.commonutils.type;

import it.unimi.dsi.fastutil.objects.ObjectIterator;
import it.unimi.dsi.fastutil.objects.ObjectIterators;
import it.unimi.dsi.fastutil.objects.ObjectOpenHashSet;
import it.unimi.dsi.fastutil.objects.ObjectSet;
import it.unimi.dsi.fastutil.objects.ObjectSets;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.function.Consumer;
import java.util.stream.Stream;
import org.jetbrains.annotations.NotNull;

public interface UnmodifiableSet<K> extends UnmodifiableIterableSet<K> {

	boolean contains(Object value);

	@NotNull
	ObjectIterator<K> fastIterator();

	void forEach(Consumer<? super K> action);

	static <K> UnmodifiableSet<K> of(K[] values) {
		int valuesSize = (values != null) ? values.length : 0;

		if (valuesSize == 0) {
			// return mutable map
			return new EmptyUnmodifiableSet<>();
		}

		return new MappedUnmodifiableSet<>(new ObjectOpenHashSet<>(values, 1.0f));
	}

	static <K> UnmodifiableSet<K> of(Set<K> set) {
		return new MappedUnmodifiableSet<K>(set);
	}

	class EmptyUnmodifiableSet<K> implements UnmodifiableSet<K> {

		private EmptyUnmodifiableSet() {}

		@Override
		public int size() {
			return 0;
		}

		@Override
		public boolean isEmpty() {
			return true;
		}

		@Override
		public boolean contains(Object value) {
			return false;
		}

		@Override
		public void forEach(Consumer<? super K> action) {

		}

		@NotNull
		@Override
		public Iterator<K> iterator() {
			return new Iterator<>() {
				@Override
				public boolean hasNext() {
					return false;
				}

				@Override
				public K next() {
					throw new NoSuchElementException();
				}
			};
		}

		@NotNull
		@Override
		public ObjectIterator<K> fastIterator() {
			return new ObjectIterator<>() {
				@Override
				public boolean hasNext() {
					return false;
				}

				@Override
				public K next() {
					throw new NoSuchElementException();
				}
			};
		}

		@Override
		public Set<K> toUnmodifiableSet() {
			//noinspection unchecked
			return new HashSet<>();
		}

		@Override
		public Stream<K> stream() {
			return Stream.empty();
		}

		@Override
		public <V> UnmodifiableIterableMap<K, V> toUnmodifiableIterableMapSetValues(V[] values) {
			return UnmodifiableIterableMap.of(null, values);
		}

		@Override
		public <K2> UnmodifiableIterableMap<K2, K> toUnmodifiableIterableMapSetKeys(K2[] keys) {
			return UnmodifiableIterableMap.of(keys, null);
		}

		@Override
		public <V> UnmodifiableMap<K, V> toUnmodifiableMapSetValues(V[] values) {
			return UnmodifiableMap.of(null, values);
		}

		@Override
		public <K2> UnmodifiableMap<K2, K> toUnmodifiableMapSetKeys(K2[] keys) {
			return UnmodifiableMap.of(keys, null);
		}
	}

	class MappedUnmodifiableSet<K> implements UnmodifiableSet<K> {

		private final Set<K> set;

		private MappedUnmodifiableSet(@NotNull Set<K> set) {
			this.set = set;
		}

		@Override
		public int size() {
			return set.size();
		}

		@Override
		public boolean isEmpty() {
			return set.isEmpty();
		}

		@Override
		public boolean contains(Object key) {
			//noinspection SuspiciousMethodCalls
			return set.contains(key);
		}

		@Override
		public void forEach(Consumer<? super K> action) {
			set.forEach(action);
		}

		@Override
		public Set<K> toUnmodifiableSet() {
			return Collections.unmodifiableSet(set);
		}

		@NotNull
		@Override
		public Iterator<K> iterator() {
			return set.iterator();
		}

		@NotNull
		@Override
		public ObjectIterator<K> fastIterator() {
			if (set instanceof ObjectSet) {
				return ((ObjectSet<K>) set).iterator();
			} else {
				return ObjectIterators.asObjectIterator(set.iterator());
			}
		}

		@Override
		public Stream<K> stream() {
			return set.stream();
		}

		@Override
		public <V> UnmodifiableIterableMap<K, V> toUnmodifiableIterableMapSetValues(V[] values) {
			return UnmodifiableIterableMap.ofObjects(set.toArray(), values);
		}

		@Override
		public <K2> UnmodifiableIterableMap<K2, K> toUnmodifiableIterableMapSetKeys(K2[] keys) {
			return UnmodifiableIterableMap.ofObjects(keys, set.toArray());
		}

		@Override
		public <V> UnmodifiableMap<K, V> toUnmodifiableMapSetValues(V[] values) {
			return UnmodifiableMap.ofObjects(set.toArray(), values);
		}

		@Override
		public <K2> UnmodifiableMap<K2, K> toUnmodifiableMapSetKeys(K2[] keys) {
			return UnmodifiableMap.ofObjects(keys, set.toArray());
		}
	}
}