// ***************************************************************************************************************************
// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
// * distributed with this work for additional information regarding copyright ownership.  The ASF licenses this file        *
// * to you 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 org.apache.juneau.internal;

import static java.util.Collections.*;
import static java.util.stream.Collectors.*;

import java.util.*;

import org.apache.juneau.utils.*;

/**
 * A linked hashmap with reverse key lookup by value.
 *
 * @param <K> The key type.
 * @param <V> The value type.
 */
public class BiMap<K,V> implements Map<K,V> {

   //-----------------------------------------------------------------------------------------------------------------
   // Static
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Create a new builder for this class.
    *
    * @param <K> The key type.
    * @param <V> The value type.
    * @return A new builder.
    */
   public static <K,V> Builder<K,V> create() {
      return new Builder<>();
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Builder
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Builder class.
    *
    * @param <K> The key type.
    * @param <V> The value type.
    */
   public static class Builder<K,V> {
      final HashMap<K,V> map = new LinkedHashMap<>();
      boolean unmodifiable;

      /**
       * Adds a value to this map.
       *
       * @param key The key.
       * @param value The value.
       * @return This object.
       */
      public Builder<K,V> add(K key, V value) {
         map.put(key, value);
         return this;
      }

      /**
       * Makes this map unmodifiable.
       *
       * @return This object.
       */
      public Builder<K,V> unmodifiable() {
         unmodifiable = true;
         return this;
      }

      /**
       * Build the differences.
       *
       * @return A new {@link BeanDiff} object.
       */
      public BiMap<K,V> build() {
         return new BiMap<>(this);
      }

   }

   //-----------------------------------------------------------------------------------------------------------------
   // Instance
   //-----------------------------------------------------------------------------------------------------------------

   private final Map<K,V> forward;
   private final Map<V,K> reverse;

   /**
    * Constructor.
    *
    * @param builder The builder for this object.
    */
   public BiMap(Builder<K,V> builder) {
      Map<K,V> forward = builder.map.entrySet().stream().filter(x -> x.getKey() != null && x.getValue() != null).collect(toMap(Map.Entry::getKey, Map.Entry::getValue));
      Map<V,K> reverse = builder.map.entrySet().stream().filter(x -> x.getKey() != null && x.getValue() != null).collect(toMap(Map.Entry::getValue, Map.Entry::getKey));
      this.forward = builder.unmodifiable ? unmodifiableMap(forward) : forward;
      this.reverse = builder.unmodifiable ? unmodifiableMap(reverse) : reverse;
   }

   /**
    * Gets the key that is currently mapped to the specified value.
    *
    * @param value The value to return.
    * @return The key matching the value.
    */
   public K getKey(V value) {
      return reverse.get(value);
   }


   @Override /* Map */
   public int size() {
      return forward.size();
   }

   @Override /* Map */
   public boolean isEmpty() {
      return forward.isEmpty();
   }

   @Override /* Map */
   public boolean containsKey(Object key) {
      return forward.containsKey(key);
   }

   @Override /* Map */
   public boolean containsValue(Object value) {
      return reverse.containsKey(value);
   }

   @Override /* Map */
   public V get(Object key) {
      return forward.get(key);
   }

   @Override /* Map */
   public V put(K key, V value) {
      reverse.put(value, key);
      return forward.put(key, value);
   }

   @Override /* Map */
   public V remove(Object key) {
      V value = forward.remove(key);
      reverse.remove(value);
      return value;
   }

   @Override /* Map */
   public void putAll(Map<? extends K,? extends V> m) {
      forward.putAll(m);
      m.entrySet().forEach(x -> reverse.put(x.getValue(), x.getKey()));
   }

   @Override /* Map */
   public void clear() {
      forward.clear();
      reverse.clear();
   }

   @Override /* Map */
   public Set<K> keySet() {
      return forward.keySet();
   }

   @Override /* Map */
   public Collection<V> values() {
      return forward.values();
   }

   @Override /* Map */
   public Set<Entry<K,V>> entrySet() {
      return forward.entrySet();
   }
}