/*
    * 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
    *
    *      https://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.commons.collections4.collection;
  
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.Objects;
  import java.util.function.Predicate;
  
  import org.apache.commons.collections4.MultiMap;
  import org.apache.commons.collections4.Transformer;
  import org.apache.commons.collections4.map.MultiValueMap;
  
  /**
   * An IndexedCollection is a Map-like view onto a Collection. It accepts a
   * keyTransformer to define how the keys are converted from the values.
   * <p>
   * Modifications made to this decorator modify the index as well as the
   * decorated {@link Collection}. However, modifications to the underlying
   * {@link Collection} will not update the index and it will get out of sync.
   * </p>
   * <p>
   * If modification of the decorated {@link Collection} is unavoidable, then a
   * call to {@link #reindex()} will update the index to the current contents of
   * the {@link Collection}.
   * </p>
   *
   * @param <K> The type of object in the index.
   * @param <C> The type of object in the collection.
   * @since 4.0
   */
  public class IndexedCollection<K, C> extends AbstractCollectionDecorator<C> {
  
      // TODO: replace with MultiValuedMap
  
      /** Serialization version */
      private static final long serialVersionUID = -5512610452568370038L;
  
      /**
       * Creates an {@link IndexedCollection} for a non-unique index.
       *
       * @param <K>            the index object type.
       * @param <C>            the collection type.
       * @param coll           The decorated {@link Collection}.
       * @param keyTransformer The {@link Transformer} for generating index keys.
       * @return The created {@link IndexedCollection}.
       */
      public static <K, C> IndexedCollection<K, C> nonUniqueIndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer) {
          return new IndexedCollection<>(coll, keyTransformer, MultiValueMap.<K, C>multiValueMap(new HashMap<>()), false);
      }
  
      /**
       * Creates an {@link IndexedCollection} for a unique index.
       * <p>
       * If an element is added, which maps to an existing key, an {@link IllegalArgumentException} will be thrown.
       * </p>
       *
       * @param <K>            the index object type.
       * @param <C>            the collection type.
       * @param coll           The decorated {@link Collection}.
       * @param keyTransformer The {@link Transformer} for generating index keys.
       * @return The created {@link IndexedCollection}.
       */
      public static <K, C> IndexedCollection<K, C> uniqueIndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer) {
          return new IndexedCollection<>(coll, keyTransformer, MultiValueMap.<K, C>multiValueMap(new HashMap<>()), true);
      }
  
      /** The {@link Transformer} for generating index keys. */
      private final Transformer<C, K> keyTransformer;
  
      /** The map of indexes to collected objects. */
      private final MultiMap<K, C> index;
  
      /** The uniqueness constraint for the index. */
      private final boolean uniqueIndex;
  
      /**
       * Creates a {@link IndexedCollection}.
       *
       * @param coll  decorated {@link Collection}.
       * @param keyTransformer  {@link Transformer} for generating index keys.
       * @param map  map to use as index.
       * @param uniqueIndex  if the index shall enforce uniqueness of index keys.
       */
     public IndexedCollection(final Collection<C> coll, final Transformer<C, K> keyTransformer, final MultiMap<K, C> map, final boolean uniqueIndex) {
         super(coll);
         this.keyTransformer = keyTransformer;
         this.index = map;
         this.uniqueIndex = uniqueIndex;
         reindex();
     }
 
     /**
      * {@inheritDoc}
      *
      * @throws IllegalArgumentException if the object maps to an existing key and the index
      *   enforces a uniqueness constraint.
      */
     @Override
     public boolean add(final C object) {
         final K key = toValidKey(object);
         final boolean added = super.add(object);
         if (added) {
             index.put(key, object);
         }
         return added;
     }
 
     @Override
     public boolean addAll(final Collection<? extends C> coll) {
         boolean changed = false;
         for (final C c: coll) {
             changed |= add(c);
         }
         return changed;
     }
 
     /**
      * Provides checking for adding the index.
      *
      * @param object The object to index.
      * @throws IllegalArgumentException if the object maps to an existing key and the index
      *   enforces a uniqueness constraint.
      */
     private void addToIndex(final C object) {
         index.put(toValidKey(object), object);
     }
 
     @Override
     public void clear() {
         super.clear();
         index.clear();
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * Note: uses the index for fast lookup.
      * </p>
      */
     @SuppressWarnings("unchecked")
     @Override
     public boolean contains(final Object object) {
         return index.containsKey(keyTransformer.apply((C) object));
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * Note: uses the index for fast lookup.
      * </p>
      */
     @Override
     public boolean containsAll(final Collection<?> coll) {
         return coll.stream().allMatch(this::contains);
     }
 
     /**
      * Gets the element associated with the given key.
      * <p>
      * In case of a non-unique index, this method will return the first
      * value associated with the given key. To retrieve all elements associated
      * with a key, use {@link #values(Object)}.
      * </p>
      *
      * @param key  key to look up.
      * @return element found.
      * @see #values(Object)
      */
     public C get(final K key) {
         @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection
         final Collection<C> coll = (Collection<C>) index.get(key);
         return coll == null ? null : coll.iterator().next();
     }
 
     /**
      * Clears the index and re-indexes the entire decorated {@link Collection}.
      */
     public void reindex() {
         index.clear();
         decorated().forEach(this::addToIndex);
     }
 
     @SuppressWarnings("unchecked")
     @Override
     public boolean remove(final Object object) {
         final boolean removed = super.remove(object);
         if (removed) {
             removeFromIndex((C) object);
         }
         return removed;
     }
 
     @Override
     public boolean removeAll(final Collection<?> coll) {
         boolean changed = false;
         for (final Object o : coll) {
             changed |= remove(o);
         }
         return changed;
     }
 
     /**
      * Removes an object from the index.
      *
      * @param object The object to remove.
      */
     private void removeFromIndex(final C object) {
         index.removeMapping(keyTransformer.apply(object), object);
     }
 
     /**
      * @since 4.4
      */
     @Override
     public boolean removeIf(final Predicate<? super C> filter) {
         if (Objects.isNull(filter)) {
             return false;
         }
         boolean changed = false;
         final Iterator<C> it = iterator();
         while (it.hasNext()) {
             if (filter.test(it.next())) {
                 it.remove();
                 changed = true;
             }
         }
         if (changed) {
             reindex();
         }
         return changed;
     }
 
     @Override
     public boolean retainAll(final Collection<?> coll) {
         final boolean changed = super.retainAll(coll);
         if (changed) {
             reindex();
         }
         return changed;
     }
 
     private K toValidKey(final C object) {
         final K key = keyTransformer.apply(object);
         if (uniqueIndex && index.containsKey(key)) {
             throw new IllegalArgumentException("Duplicate key in uniquely indexed collection.");
         }
         return key;
     }
 
     /**
      * Gets all elements associated with the given key.
      *
      * @param key  key to look up.
      * @return A collection of elements found, or null if {@code contains(key) == false}.
      */
     @SuppressWarnings("unchecked") // index is a MultiMap which returns a Collection.
     public Collection<C> values(final K key) {
         return (Collection<C>) index.get(key);
     }
 
 }