/*
 * 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 com.google.common.collect;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collector;
import java.util.stream.Collectors;

/**
 * A {@link BiMap} whose contents will never change, with many other important properties detailed
 * at {@link ImmutableCollection}.
 *
 * @author Jared Levy
 * @since 2.0
 */
@GwtCompatible(serializable = true, emulated = true)
public abstract class ImmutableBiMap<K, V> extends ImmutableBiMapFauxverideShim<K, V>
    implements BiMap<K, V> {

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableBiMap} whose
   * keys and values are the result of applying the provided mapping functions to the input
   * elements. Entries appear in the result {@code ImmutableBiMap} in encounter order.
   *
   * <p>If the mapped keys or values contain duplicates
   * (according to {@link Object#equals(Object)}, an {@code IllegalArgumentException} is thrown
   * when the collection operation is performed. (This differs from the {@code Collector} returned
   * by {@link Collectors#toMap(Function, Function)}, which throws an
   * {@code IllegalStateException}.)
   *
   * @since 21.0
   */
  @Beta
  public static <T, K, V> Collector<T, ?, ImmutableBiMap<K, V>> toImmutableBiMap(
      Function<? super T, ? extends K> keyFunction,
      Function<? super T, ? extends V> valueFunction) {
    return CollectCollectors.toImmutableBiMap(keyFunction, valueFunction);
  }

  /**
   * Returns the empty bimap.
   */
  // Casting to any type is safe because the set will never hold any elements.
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableBiMap<K, V> of() {
    return (ImmutableBiMap<K, V>) RegularImmutableBiMap.EMPTY;
  }

  /**
   * 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 RegularImmutableBiMap.fromEntries(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 RegularImmutableBiMap.fromEntries(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 RegularImmutableBiMap.fromEntries(
        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 RegularImmutableBiMap.fromEntries(
        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>By default, a {@code Builder} will generate bimaps that iterate over entries in the order
   * they were inserted into the builder.  For example, in the above example,
   * {@code WORD_TO_INT.entrySet()} is guaranteed to iterate over the entries in the order
   * {@code "one"=1, "two"=2, "three"=3}, and {@code keySet()} and {@code values()} respect the same
   * order. If you want a different order, consider using
   * {@link #orderEntriesByValue(Comparator)}, which changes this builder to sort
   * entries by value.
   *
   * <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
   */
  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() {}

    Builder(int size) {
      super(size);
    }

    /**
     * Associates {@code key} with {@code value} in the built bimap. Duplicate
     * keys or values are not allowed, and will cause {@link #build} to fail.
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> put(K key, V value) {
      super.put(key, value);
      return this;
    }

    /**
     * Adds the given {@code entry} to the bimap.  Duplicate keys or values
     * are not allowed, and will cause {@link #build} to fail.
     *
     * @since 19.0
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> put(Entry<? extends K, ? extends V> entry) {
      super.put(entry);
      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
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> putAll(Map<? extends K, ? extends V> map) {
      super.putAll(map);
      return this;
    }

    /**
     * Adds all of the given entries to the built bimap.  Duplicate keys or
     * values are not allowed, and will cause {@link #build} to fail.
     *
     * @throws NullPointerException if any key, value, or entry is null
     * @since 19.0
     */
    @CanIgnoreReturnValue
    @Beta
    @Override
    public Builder<K, V> putAll(Iterable<? extends Entry<? extends K, ? extends V>> entries) {
      super.putAll(entries);
      return this;
    }

    /**
     * Configures this {@code Builder} to order entries by value according to the specified
     * comparator.
     *
     * <p>The sort order is stable, that is, if two entries have values that compare
     * as equivalent, the entry that was inserted first will be first in the built map's
     * iteration order.
     *
     * @throws IllegalStateException if this method was already called
     * @since 19.0
     */
    @CanIgnoreReturnValue
    @Beta
    @Override
    public Builder<K, V> orderEntriesByValue(Comparator<? super V> valueComparator) {
      super.orderEntriesByValue(valueComparator);
      return this;
    }

    @Override
    @CanIgnoreReturnValue
    Builder<K, V> combine(ImmutableMap.Builder<K, V> builder) {
      super.combine(builder);
      return this;
    }

    /**
     * Returns a newly-created immutable bimap.  The iteration order of the returned bimap is
     * the order in which entries were inserted into the builder, unless
     * {@link #orderEntriesByValue} was called, in which case entries are sorted by value.
     *
     * @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:
          /*
           * If entries is full, then this implementation may end up using the entries array
           * directly and writing over the entry objects with non-terminal entries, but this is
           * safe; if this Builder is used further, it will grow the entries array (so it can't
           * affect the original array), and future build() calls will always copy any entry
           * objects that cannot be safely reused.
           */
          if (valueComparator != null) {
            if (entriesUsed) {
              entries = Arrays.copyOf(entries, size);
            }
            Arrays.sort(
                entries,
                0,
                size,
                Ordering.from(valueComparator).onResultOf(Maps.<V>valueFunction()));
          }
          entriesUsed = size == entries.length;
          return RegularImmutableBiMap.fromEntryArray(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>The returned {@code BiMap} iterates over entries in the same order as the
   * {@code entrySet} of the original map.
   *
   * <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 or two values have the same
   *     key
   * @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) {
      @SuppressWarnings("unchecked") // safe since map is not writable
      ImmutableBiMap<K, V> bimap = (ImmutableBiMap<K, V>) map;
      // TODO(lowasser): 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;
      }
    }
    return copyOf(map.entrySet());
  }

  /**
   * Returns an immutable bimap containing the given entries.  The returned bimap iterates over
   * entries in the same order as the original iterable.
   *
   * @throws IllegalArgumentException if two keys have the same value or two
   *         values have the same key
   * @throws NullPointerException if any key, value, or entry is null
   * @since 19.0
   */
  @Beta
  public static <K, V> ImmutableBiMap<K, V> copyOf(
      Iterable<? extends Entry<? extends K, ? extends V>> entries) {
    @SuppressWarnings("unchecked") // we'll only be using getKey and getValue, which are covariant
    Entry<K, V>[] entryArray = (Entry<K, V>[]) Iterables.toArray(entries, EMPTY_ENTRY_ARRAY);
    switch (entryArray.length) {
      case 0:
        return of();
      case 1:
        Entry<K, V> entry = entryArray[0];
        return of(entry.getKey(), entry.getValue());
      default:
        /*
         * The current implementation will end up using entryArray directly, though it will write
         * over the (arbitrary, potentially mutable) Entry objects actually stored in entryArray.
         */
        return RegularImmutableBiMap.fromEntries(entryArray);
    }
  }

  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, in the same order they appear in {@link
   * #entrySet}.
   */
  @Override
  public ImmutableSet<V> values() {
    return inverse().keySet();
  }

  @Override
  final ImmutableSet<V> createValues() {
    throw new AssertionError("should never be called");
  }

  /**
   * Guaranteed to throw an exception and leave the bimap unmodified.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @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);
  }
}