/*
 * 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.base.Preconditions.checkNotNull;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

/**
 * GWT emulated version of {@link ImmutableSet}.  For the unsorted sets, they
 * are thin wrapper around {@link java.util.Collections#emptySet()}, {@link
 * Collections#singleton(Object)} and {@link java.util.LinkedHashSet} for
 * empty, singleton and regular sets respectively.  For the sorted sets, it's
 * a thin wrapper around {@link java.util.TreeSet}.
 *
 * @see ImmutableSortedSet
 *
 * @author Hayward Chan
 */
@SuppressWarnings("serial")  // Serialization only done in GWT.
public abstract class ImmutableSet<E> extends ForwardingImmutableCollection<E>
    implements Set<E> {

  ImmutableSet(Set<E> delegate) {
    super(Collections.unmodifiableSet(delegate));
  }

  ImmutableSet() {
    this(Collections.<E>emptySet());
  }

  // Casting to any type is safe because the set will never hold any elements.
  @SuppressWarnings({"unchecked"})
  public static <E> ImmutableSet<E> of() {
    return (ImmutableSet<E>) EmptyImmutableSet.INSTANCE;
  }

  public static <E> ImmutableSet<E> of(E element) {
    return new SingletonImmutableSet<E>(element);
  }

  @SuppressWarnings("unchecked")
  public static <E> ImmutableSet<E> of(E e1, E e2) {
    return create(e1, e2);
  }

  @SuppressWarnings("unchecked")
  public static <E> ImmutableSet<E> of(E e1, E e2, E e3) {
    return create(e1, e2, e3);
  }

  @SuppressWarnings("unchecked")
  public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4) {
    return create(e1, e2, e3, e4);
  }

  @SuppressWarnings("unchecked")
  public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4, E e5) {
    return create(e1, e2, e3, e4, e5);
  }

  @SuppressWarnings("unchecked")
  public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4, E e5, E e6,
      E... others) {
    int size = others.length + 6;
    List<E> all = new ArrayList<E>(size);
    Collections.addAll(all, e1, e2, e3, e4, e5, e6);
    Collections.addAll(all, others);
    return copyOf(all.iterator());
  }

  /** @deprecated */
  @Deprecated public static <E> ImmutableSet<E> of(E[] elements) {
    return copyOf(elements);
  }

  public static <E> ImmutableSet<E> copyOf(E[] elements) {
    checkNotNull(elements);
    switch (elements.length) {
      case 0:
        return of();
      case 1:
        return of(elements[0]);
      default:
        return create(elements);
    }
  }

  public static <E> ImmutableSet<E> copyOf(Collection<? extends E> elements) {
    Iterable<? extends E> iterable = elements;
    return copyOf(iterable);
  }

  public static <E> ImmutableSet<E> copyOf(Iterable<? extends E> elements) {
    if (elements instanceof ImmutableSet
        && !(elements instanceof ImmutableSortedSet)) {
      @SuppressWarnings("unchecked") // all supported methods are covariant
      ImmutableSet<E> set = (ImmutableSet<E>) elements;
      return set;
    }
    return copyOf(elements.iterator());
  }

  public static <E> ImmutableSet<E> copyOf(Iterator<? extends E> elements) {
    if (!elements.hasNext()) {
      return of();
    }
    E first = elements.next();
    if (!elements.hasNext()) {
      // TODO: Remove "ImmutableSet.<E>" when eclipse bug is fixed.
      return ImmutableSet.<E>of(first);
    }

    Set<E> delegate = Sets.newLinkedHashSet();
    delegate.add(checkNotNull(first));
    do {
      delegate.add(checkNotNull(elements.next()));
    } while (elements.hasNext());

    return unsafeDelegate(delegate);
  }

  // Factory methods that skips the null checks on elements, only used when
  // the elements are known to be non-null.
  static <E> ImmutableSet<E> unsafeDelegate(Set<E> delegate) {
    switch (delegate.size()) {
      case 0:
        return of();
      case 1:
        return new SingletonImmutableSet<E>(delegate.iterator().next());
      default:
        return new RegularImmutableSet<E>(delegate);
    }
  }

  private static <E> ImmutableSet<E> create(E... elements) {
    // Create the set first, to remove duplicates if necessary.
    Set<E> set = Sets.newLinkedHashSet();
    Collections.addAll(set, elements);
    for (E element : set) {
      checkNotNull(element);
    }

    switch (set.size()) {
      case 0:
        return of();
      case 1:
        return new SingletonImmutableSet<E>(set.iterator().next());
      default:
        return new RegularImmutableSet<E>(set);
    }
  }

  @Override public boolean equals(Object obj) {
    return Sets.equalsImpl(this, obj);
  }

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

  public static <E> Builder<E> builder() {
    return new Builder<E>();
  }

  public static class Builder<E> extends ImmutableCollection.Builder<E> {
    // accessed directly by ImmutableSortedSet
    final ArrayList<E> contents = Lists.newArrayList();

    public Builder() {}

    @Override public Builder<E> add(E element) {
      contents.add(checkNotNull(element));
      return this;
    }

    @Override public Builder<E> add(E... elements) {
      checkNotNull(elements); // for GWT
      contents.ensureCapacity(contents.size() + elements.length);
      super.add(elements);
      return this;
    }

    @Override public Builder<E> addAll(Iterable<? extends E> elements) {
      if (elements instanceof Collection) {
        Collection<?> collection = (Collection<?>) elements;
        contents.ensureCapacity(contents.size() + collection.size());
      }
      super.addAll(elements);
      return this;
    }

    @Override public Builder<E> addAll(Iterator<? extends E> elements) {
      super.addAll(elements);
      return this;
    }

    @Override public ImmutableSet<E> build() {
      return copyOf(contents.iterator());
    }
  }
}