/*
 * Copyright (C) 2008 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 common.collect;

/**
 * Bimap with no mappings.
 *
 * @author Jared Levy
 */

// // uses writeReplace(), not default serialization
final class EmptyImmutableMap extends ImmutableMap<Object, Object> {
  static final EmptyImmutableMap INSTANCE = new EmptyImmutableMap();

  private EmptyImmutableMap() {}
  
//  @Override public ImmutableBiMap<Object, Object> inverse() {
//    return this;
//  }
  
  @Override
  public int size() {
    return 0;
  }

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

  @Override
  public Object get(Object key) {
    return null;
  }

  @Override
  public ImmutableSet<Entry<Object, Object>> entrySet() {
    return ImmutableSet.of();
  }

  @Override
  ImmutableSet<Entry<Object, Object>> createEntrySet() {
    throw new AssertionError("should never be called");
  }

//  @Override
//  public ImmutableSetMultimap<Object, Object> asMultimap() {
//    return ImmutableSetMultimap.of();
//  }

  @Override
  public ImmutableSet<Object> keySet() {
    return ImmutableSet.of();
  }

  @Override
  boolean isPartialView() {
    return false;
  }
  
//  Object readResolve() {
//    return INSTANCE; // preserve singleton property
//  }
  /**
   * Returns the empty bimap.
   */
  // Casting to any type is safe because the set will never hold any elements.
//  
//  public static <K, V> ImmutableBiMap<K, V> of() {
//    return (ImmutableBiMap<K, V>) EmptyImmutableBiMap.INSTANCE;
//  }

  /**
   * Returns an immutable bimap containing a single entry.
   */
//  public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1) {
//    return new SingletonImmutableBiMap<K, V>(k1, v1);
//  }

  /**
   * Returns an immutable map containing the given entries, in order.
   *
   * @throws IllegalArgumentException if duplicate keys or values are added
   */
//  public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2) {
//    return new RegularImmutableBiMap<K, V>(entryOf(k1, v1), entryOf(k2, v2));
//  }
//
//  /**
//   * Returns an immutable map containing the given entries, in order.
//   *
//   * @throws IllegalArgumentException if duplicate keys or values are added
//   */
//  public static <K, V> ImmutableBiMap<K, V> of(
//      K k1, V v1, K k2, V v2, K k3, V v3) {
//    return new RegularImmutableBiMap<K, V>(entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3));
//  }
//
//  /**
//   * Returns an immutable map containing the given entries, in order.
//   *
//   * @throws IllegalArgumentException if duplicate keys or values are added
//   */
//  public static <K, V> ImmutableBiMap<K, V> of(
//      K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
//    return new RegularImmutableBiMap<K, V>(entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3),
//        entryOf(k4, v4));
//  }
//
//  /**
//   * Returns an immutable map containing the given entries, in order.
//   *
//   * @throws IllegalArgumentException if duplicate keys or values are added
//   */
//  public static <K, V> ImmutableBiMap<K, V> of(
//      K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
//    return new RegularImmutableBiMap<K, V>(entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3),
//        entryOf(k4, v4), entryOf(k5, v5));
//  }

  // looking for of() with > 5 entries? Use the builder instead.

  /**
   * Returns a new builder. The generated builder is equivalent to the builder
   * created by the {@link Builder} constructor.
   */
//  public static <K, V> Builder<K, V> builder() {
//    return new Builder<K, V>();
//  }

  /**
   * A builder for creating immutable bimap instances, especially {@code public
   * static final} bimaps ("constant bimaps"). Example: <pre>   {@code
   *
   *   static final ImmutableBiMap<String, Integer> WORD_TO_INT =
   *       new ImmutableBiMap.Builder<String, Integer>()
   *           .put("one", 1)
   *           .put("two", 2)
   *           .put("three", 3)
   *           .build();}</pre>
   *
   * <p>For <i>small</i> immutable bimaps, the {@code ImmutableBiMap.of()} methods
   * are even more convenient.
   *
   * <p>Builder instances can be reused - it is safe to call {@link #build}
   * multiple times to build multiple bimaps in series. Each bimap is a superset
   * of the bimaps created before it.
   *
   * @since 2.0 (imported from Google Collections Library)
   */
//  public static final class Builder<K, V> extends ImmutableMap.Builder<K, V> {
//
//    /**
//     * Creates a new builder. The returned builder is equivalent to the builder
//     * generated by {@link ImmutableBiMap#builder}.
//     */
//    public Builder() {}
//
//    /**
//     * Associates {@code key} with {@code value} in the built bimap. Duplicate
//     * keys or values are not allowed, and will cause {@link #build} to fail.
//     */
//    @Override public Builder<K, V> put(K key, V value) {
//      super.put(key, value);
//      return this;
//    }
//
//    /**
//     * Associates all of the given map's keys and values in the built bimap.
//     * Duplicate keys or values are not allowed, and will cause {@link #build}
//     * to fail.
//     *
//     * @throws NullPointerException if any key or value in {@code map} is null
//     */
//    @Override public Builder<K, V> putAll(Map<? extends K, ? extends V> map) {
//      super.putAll(map);
//      return this;
//    }
//
//    /**
//     * Returns a newly-created immutable bimap.
//     *
//     * @throws IllegalArgumentException if duplicate keys or values were added
//     */
//    @Override public ImmutableBiMap<K, V> build() {
//      switch (size) {
//        case 0:
//          return of();
//        case 1:
//          return of(entries[0].getKey(), entries[0].getValue());
//        default:
//          return new RegularImmutableBiMap<K, V>(size, entries);
//      }
//    }
//  }

  /**
   * Returns an immutable bimap containing the same entries as {@code map}. If
   * {@code map} somehow contains entries with duplicate keys (for example, if
   * it is a {@code SortedMap} whose comparator is not <i>consistent with
   * equals</i>), the results of this method are undefined.
   *
   * <p>Despite the method name, this method attempts to avoid actually copying
   * the data when it is safe to do so. The exact circumstances under which a
   * copy will or will not be performed are undocumented and subject to change.
   *
   * @throws IllegalArgumentException if two keys have the same value
   * @throws NullPointerException if any key or value in {@code map} is null
   */
//  public static <K, V> ImmutableBiMap<K, V> copyOf(
//      Map<? extends K, ? extends V> map) {
//    if (map instanceof ImmutableBiMap) {
//       // safe since map is not writable
//      ImmutableBiMap<K, V> bimap = (ImmutableBiMap<K, V>) map;
//      // TODO(user): if we need to make a copy of a BiMap because the
//      // forward map is a view, don't make a copy of the non-view delegate map
//      if (!bimap.isPartialView()) {
//        return bimap;
//      }
//    }
//    Entry<?, ?>[] entries = map.entrySet().toArray(EMPTY_ENTRY_ARRAY);
//    switch (entries.length) {
//      case 0:
//        return of();
//      case 1:
//         // safe covariant cast in this context
//        Entry<K, V> entry = (Entry<K, V>) entries[0];
//        return of(entry.getKey(), entry.getValue());
//      default:
//        return new RegularImmutableBiMap<K, V>(entries);
//    }
//  }

//  private static final Entry<?, ?>[] EMPTY_ENTRY_ARRAY = new Entry<?, ?>[0];

//  ImmutableBiMap() {}

  /**
   * {@inheritDoc}
   *
   * <p>The inverse of an {@code ImmutableBiMap} is another
   * {@code ImmutableBiMap}.
   */
//  @Override
//  public abstract ImmutableBiMap<V, K> inverse();

  /**
   * Returns an immutable set of the values in this map. The values are in the
   * same order as the parameters used to build this map.
   */
  @Override public ImmutableSet<Object> values() {
    return ImmutableSet.of();
  }

  /**
   * Guaranteed to throw an exception and leave the bimap unmodified.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
//  @Deprecated
//  @Override
//  public V forcePut(K key, V value) {
//    throw new UnsupportedOperationException();
//  }

  /**
   * Serialized type for all ImmutableBiMap instances. It captures the logical
   * contents and they are reconstructed using public factory methods. This
   * ensures that the implementation types remain as implementation details.
   *
   * Since the bimap is immutable, ImmutableBiMap doesn't require special logic
   * for keeping the bimap and its inverse in sync during serialization, the way
   * AbstractBiMap does.
   */
//  private static class SerializedForm extends ImmutableMap.SerializedForm {
//    SerializedForm(ImmutableBiMap<?, ?> bimap) {
//      super(bimap);
//    }
//    @Override Object readResolve() {
//      Builder<Object, Object> builder = new Builder<Object, Object>();
//      return createMap(builder);
//    }
//    private static final long serialVersionUID = 0;
//  }
//
//  @Override Object writeReplace() {
//    return new SerializedForm(this);
//  }
}
