/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.collect.Iterables.getOnlyElement;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.errorprone.annotations.concurrent.LazyInit;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.util.Collection;
import java.util.EnumSet;
import java.util.Spliterator;
import java.util.function.Consumer;
import org.jspecify.annotations.Nullable;

/**
 * Implementation of {@link ImmutableSet} backed by a non-empty {@link java.util.EnumSet}.
 *
 * @author Jared Levy
 */
@GwtCompatible
@SuppressWarnings("serial") // we're overriding default serialization
final class ImmutableEnumSet<E extends Enum<E>> extends ImmutableSet<E> {
  static <E extends Enum<E>> ImmutableSet<E> asImmutable(EnumSet<E> set) {
    switch (set.size()) {
      case 0:
        return ImmutableSet.of();
      case 1:
        return ImmutableSet.of(getOnlyElement(set));
      default:
        return new ImmutableEnumSet<>(set);
    }
  }

  /*
   * Notes on EnumSet and <E extends Enum<E>>:
   *
   * This class isn't an arbitrary ForwardingImmutableSet because we need to
   * know that calling {@code clone()} during deserialization will return an
   * object that no one else has a reference to, allowing us to guarantee
   * immutability. Hence, we support only {@link EnumSet}.
   */
  private final transient EnumSet<E> delegate;

  private ImmutableEnumSet(EnumSet<E> delegate) {
    this.delegate = delegate;
  }

  @Override
  boolean isPartialView() {
    return false;
  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return Iterators.unmodifiableIterator(delegate.iterator());
  }

  @Override
  public Spliterator<E> spliterator() {
    return delegate.spliterator();
  }

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

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

  @Override
  public boolean contains(@Nullable Object object) {
    return delegate.contains(object);
  }

  @Override
  public boolean containsAll(Collection<?> collection) {
    if (collection instanceof ImmutableEnumSet<?>) {
      collection = ((ImmutableEnumSet<?>) collection).delegate;
    }
    return delegate.containsAll(collection);
  }

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

  @Override
  public boolean equals(@Nullable Object object) {
    if (object == this) {
      return true;
    }
    if (object instanceof ImmutableEnumSet) {
      object = ((ImmutableEnumSet<?>) object).delegate;
    }
    return delegate.equals(object);
  }

  @Override
  boolean isHashCodeFast() {
    return true;
  }

  @LazyInit private transient int hashCode;

  @Override
  public int hashCode() {
    int result = hashCode;
    return (result == 0) ? hashCode = delegate.hashCode() : result;
  }

  @Override
  public String toString() {
    return delegate.toString();
  }

  @Override
  @J2ktIncompatible // serialization
  Object writeReplace() {
    return new EnumSerializedForm<E>(delegate);
  }

  @J2ktIncompatible // serialization
  private void readObject(ObjectInputStream stream) throws InvalidObjectException {
    throw new InvalidObjectException("Use SerializedForm");
  }

  /*
   * This class is used to serialize ImmutableEnumSet instances.
   */
  @J2ktIncompatible // serialization
  private static final class EnumSerializedForm<E extends Enum<E>> implements Serializable {
    final EnumSet<E> delegate;

    EnumSerializedForm(EnumSet<E> delegate) {
      this.delegate = delegate;
    }

    Object readResolve() {
      // EJ2 #76: Write readObject() methods defensively.
      return new ImmutableEnumSet<E>(delegate.clone());
    }

    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
  }
}
