/*
    * 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.commons.collections4.set;
  
  import java.io.Serializable;
  import java.lang.reflect.Array;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Objects;
  import java.util.Set;
  import java.util.function.Predicate;
  
  import org.apache.commons.collections4.CollectionUtils;
  import org.apache.commons.collections4.iterators.EmptyIterator;
  import org.apache.commons.collections4.iterators.IteratorChain;
  import org.apache.commons.collections4.list.UnmodifiableList;
  
  /**
   * Decorates a set of other sets to provide a single unified view.
   * <p>
   * Changes made to this set will actually be made on the decorated set.
   * Add operations require the use of a pluggable strategy.
   * If no strategy is provided then add is unsupported.
   * </p>
   * <p>
   * From version 4.0, this class does not extend
   * {@link org.apache.commons.collections4.collection.CompositeCollection CompositeCollection}
   * anymore due to its input restrictions (only accepts Sets).
   * See <a href="https://issues.apache.org/jira/browse/COLLECTIONS-424">COLLECTIONS-424</a>
   * for more details.
   * </p>
   *
   * @param <E> the type of the elements in this set
   * @since 3.0
   */
  public class CompositeSet<E> implements Set<E>, Serializable {
  
      /**
       * Defines callbacks for mutation operations.
       */
      public interface SetMutator<E> extends Serializable {
  
          /**
           * Called when an object is to be added to the composite.
           *
           * @param composite  the CompositeSet being changed
           * @param sets  all of the Set instances in this CompositeSet
           * @param obj  the object being added
           * @return true if the collection is changed
           * @throws UnsupportedOperationException if add is unsupported
           * @throws ClassCastException if the object cannot be added due to its type
           * @throws NullPointerException if the object cannot be added because its null
           * @throws IllegalArgumentException if the object cannot be added
           */
          boolean add(CompositeSet<E> composite, List<Set<E>> sets, E obj);
  
          /**
           * Called when a collection is to be added to the composite.
           *
           * @param composite  the CompositeSet being changed
           * @param sets  all of the Set instances in this CompositeSet
           * @param coll  the collection being added
           * @return true if the collection is changed
           * @throws UnsupportedOperationException if add is unsupported
           * @throws ClassCastException if the object cannot be added due to its type
           * @throws NullPointerException if the object cannot be added because its null
           * @throws IllegalArgumentException if the object cannot be added
           */
          boolean addAll(CompositeSet<E> composite,
                                List<Set<E>> sets,
                                Collection<? extends E> coll);
  
          /**
           * Called when a Set is added to the CompositeSet and there is a
           * collision between existing and added sets.
           * <p>
           * If {@code added} and {@code existing} still have any intersects
           * after this method returns an IllegalArgumentException will be thrown.
           *
           * @param comp  the CompositeSet being modified
           * @param existing  the Set already existing in the composite
           * @param added  the Set being added to the composite
          * @param intersects  the intersection of the existing and added sets
          */
         void resolveCollision(CompositeSet<E> comp,
                                      Set<E> existing,
                                      Set<E> added,
                                      Collection<E> intersects);
     }
 
     /** Serialization version */
     private static final long serialVersionUID = 5185069727540378940L;
 
     /** SetMutator to handle changes to the collection */
     private SetMutator<E> mutator;
 
     /** Sets in the composite */
     private final List<Set<E>> all = new ArrayList<>();
 
     /**
      * Creates an empty CompositeSet.
      */
     public CompositeSet() {
     }
 
     /**
      * Creates a CompositeSet with just {@code set} composited.
      *
      * @param set  the initial set in the composite
      */
     public CompositeSet(final Set<E> set) {
         addComposited(set);
     }
 
     /**
      * Creates a composite set with sets as the initial set of composited Sets.
      *
      * @param sets  the initial sets in the composite
      */
     public CompositeSet(final Set<E>... sets) {
         addComposited(sets);
     }
 
     /**
      * Adds an object to the collection, throwing UnsupportedOperationException
      * unless a SetMutator strategy is specified.
      *
      * @param obj  the object to add
      * @return {@code true} if the collection was modified
      * @throws UnsupportedOperationException if SetMutator hasn't been set or add is unsupported
      * @throws ClassCastException if the object cannot be added due to its type
      * @throws NullPointerException if the object cannot be added because its null
      * @throws IllegalArgumentException if the object cannot be added
      */
     @Override
     public boolean add(final E obj) {
         if (mutator == null) {
             throw new UnsupportedOperationException(
                 "add() is not supported on CompositeSet without a SetMutator strategy");
         }
         return mutator.add(this, all, obj);
     }
 
     /**
      * Adds a collection of elements to this composite, throwing
      * UnsupportedOperationException unless a SetMutator strategy is specified.
      *
      * @param coll  the collection to add
      * @return true if the composite was modified
      * @throws UnsupportedOperationException if SetMutator hasn't been set or add is unsupported
      * @throws ClassCastException if the object cannot be added due to its type
      * @throws NullPointerException if the object cannot be added because its null
      * @throws IllegalArgumentException if the object cannot be added
      */
     @Override
     public boolean addAll(final Collection<? extends E> coll) {
         if (mutator == null) {
             throw new UnsupportedOperationException(
                 "addAll() is not supported on CompositeSet without a SetMutator strategy");
         }
         return mutator.addAll(this, all, coll);
     }
 
     /**
      * Adds a Set to this composite.
      *
      * @param set  the set to add
      * @throws IllegalArgumentException if a SetMutator is set, but fails to resolve a collision
      * @throws UnsupportedOperationException if there is no SetMutator set
      * @throws NullPointerException if {@code set} is null
      * @see SetMutator
      */
     public synchronized void addComposited(final Set<E> set) {
         if (set != null) {
             for (final Set<E> existingSet : getSets()) {
                 final Collection<E> intersects = CollectionUtils.intersection(existingSet, set);
                 if (!intersects.isEmpty()) {
                     if (this.mutator == null) {
                         throw new UnsupportedOperationException(
                                 "Collision adding composited set with no SetMutator set");
                     }
                     getMutator().resolveCollision(this, existingSet, set, intersects);
                     if (!CollectionUtils.intersection(existingSet, set).isEmpty()) {
                         throw new IllegalArgumentException(
                                 "Attempt to add illegal entry unresolved by SetMutator.resolveCollision()");
                     }
                 }
             }
             all.add(set);
         }
     }
 
     /**
      * Adds these Sets to the list of sets in this composite
      *
      * @param sets  the Sets to be appended to the composite
      */
     public void addComposited(final Set<E>... sets) {
         if (sets != null) {
             for (final Set<E> set : sets) {
                 addComposited(set);
             }
         }
     }
 
     /**
      * Adds these Sets to the list of sets in this composite.
      *
      * @param set1  the first Set to be appended to the composite
      * @param set2  the second Set to be appended to the composite
      */
     public void addComposited(final Set<E> set1, final Set<E> set2) {
         addComposited(set1);
         addComposited(set2);
     }
 
     /**
      * Removes all of the elements from this composite set.
      * <p>
      * This implementation calls {@code clear()} on each set.
      *
      * @throws UnsupportedOperationException if clear is unsupported
      */
     @Override
     public void clear() {
         for (final Collection<E> coll : all) {
             coll.clear();
         }
     }
 
     /**
      * Checks whether this composite set contains the object.
      * <p>
      * This implementation calls {@code contains()} on each set.
      *
      * @param obj  the object to search for
      * @return true if obj is contained in any of the contained sets
      */
     @Override
     public boolean contains(final Object obj) {
         for (final Set<E> item : all) {
             if (item.contains(obj)) {
                 return true;
             }
         }
         return false;
     }
 
     /**
      * Checks whether this composite contains all the elements in the specified collection.
      * <p>
      * This implementation calls {@code contains()} for each element in the
      * specified collection.
      *
      * @param coll  the collection to check for
      * @return true if all elements contained
      */
     @Override
     public boolean containsAll(final Collection<?> coll) {
         if (coll == null) {
             return false;
         }
         for (final Object item : coll) {
             if (!contains(item)) {
                 return false;
             }
         }
         return true;
     }
 
     /**
      * {@inheritDoc}
      * @see java.util.Set#equals
      */
     @Override
     public boolean equals(final Object obj) {
         if (obj instanceof Set) {
             final Set<?> set = (Set<?>) obj;
             return set.size() == this.size() && set.containsAll(this);
         }
         return false;
     }
 
     /**
      * Gets the set mutator to be used for this CompositeSet.
      * @return the set mutator
      */
     protected SetMutator<E> getMutator() {
         return mutator;
     }
 
     /**
      * Gets the sets being decorated.
      *
      * @return Unmodifiable list of all sets in this composite.
      */
     public List<Set<E>> getSets() {
         return UnmodifiableList.unmodifiableList(all);
     }
 
     /**
      * {@inheritDoc}
      * @see java.util.Set#hashCode
      */
     @Override
     public int hashCode() {
         int code = 0;
         for (final E e : this) {
             code += e == null ? 0 : e.hashCode();
         }
         return code;
     }
 
     /**
      * Checks whether this composite set is empty.
      * <p>
      * This implementation calls {@code isEmpty()} on each set.
      *
      * @return true if all of the contained sets are empty
      */
     @Override
     public boolean isEmpty() {
         for (final Set<E> item : all) {
             if (!item.isEmpty()) {
                 return false;
             }
         }
         return true;
     }
 
     /**
      * Gets an iterator over all the sets in this composite.
      * <p>
      * This implementation uses an {@code IteratorChain}.
      *
      * @return an {@code IteratorChain} instance which supports
      *  {@code remove()}. Iteration occurs over contained collections in
      *  the order they were added, but this behavior should not be relied upon.
      * @see IteratorChain
      */
     @Override
     public Iterator<E> iterator() {
         if (all.isEmpty()) {
             return EmptyIterator.<E>emptyIterator();
         }
         final IteratorChain<E> chain = new IteratorChain<>();
         all.forEach(item -> chain.addIterator(item.iterator()));
         return chain;
     }
 
     /**
      * If a {@code CollectionMutator} is defined for this CompositeSet then this
      * method will be called anyway.
      *
      * @param obj  object to be removed
      * @return true if the object is removed, false otherwise
      */
     @Override
     public boolean remove(final Object obj) {
         for (final Set<E> set : getSets()) {
             if (set.contains(obj)) {
                 return set.remove(obj);
             }
         }
         return false;
     }
 
     /**
      * Removes the elements in the specified collection from this composite set.
      * <p>
      * This implementation calls {@code removeAll} on each collection.
      *
      * @param coll  the collection to remove
      * @return true if the composite was modified
      * @throws UnsupportedOperationException if removeAll is unsupported
      */
     @Override
     public boolean removeAll(final Collection<?> coll) {
         if (CollectionUtils.isEmpty(coll)) {
             return false;
         }
         boolean changed = false;
         for (final Collection<E> item : all) {
             changed |= item.removeAll(coll);
         }
         return changed;
     }
 
     /**
      * Removes a set from those being decorated in this composite.
      *
      * @param set  set to be removed
      */
     public void removeComposited(final Set<E> set) {
         all.remove(set);
     }
 
     /**
      * @since 4.4
      */
     @Override
     public boolean removeIf(final Predicate<? super E> filter) {
         if (Objects.isNull(filter)) {
             return false;
         }
         boolean changed = false;
         for (final Collection<E> item : all) {
             changed |= item.removeIf(filter);
         }
         return changed;
     }
 
     /**
      * Retains all the elements in the specified collection in this composite set,
      * removing all others.
      * <p>
      * This implementation calls {@code retainAll()} on each collection.
      *
      * @param coll  the collection to remove
      * @return true if the composite was modified
      * @throws UnsupportedOperationException if retainAll is unsupported
      */
     @Override
     public boolean retainAll(final Collection<?> coll) {
         boolean changed = false;
         for (final Collection<E> item : all) {
             changed |= item.retainAll(coll);
         }
         return changed;
     }
 
     /**
      * Specify a SetMutator strategy instance to handle changes.
      *
      * @param mutator  the mutator to use
      */
     public void setMutator(final SetMutator<E> mutator) {
         this.mutator = mutator;
     }
 
     /**
      * Gets the size of this composite set.
      * <p>
      * This implementation calls {@code size()} on each set.
      *
      * @return total number of elements in all contained containers
      */
     @Override
     public int size() {
         int size = 0;
         for (final Set<E> item : all) {
             size += item.size();
         }
         return size;
     }
 
     /**
      * Returns an array containing all of the elements in this composite.
      *
      * @return an object array of all the elements in the collection
      */
     @Override
     public Object[] toArray() {
         final Object[] result = new Object[size()];
         int i = 0;
         for (final Iterator<E> it = iterator(); it.hasNext(); i++) {
             result[i] = it.next();
         }
         return result;
     }
 
     /**
      * Returns an object array, populating the supplied array if possible.
      * See {@code Collection} interface for full details.
      *
      * @param <T>  the type of the elements in the collection
      * @param array  the array to use, populating if possible
      * @return an array of all the elements in the collection
      */
     @Override
     @SuppressWarnings("unchecked")
     public <T> T[] toArray(final T[] array) {
         final int size = size();
         Object[] result = null;
         if (array.length >= size) {
             result = array;
         } else {
             result = (Object[]) Array.newInstance(array.getClass().getComponentType(), size);
         }
 
         int offset = 0;
         for (final Collection<E> item : all) {
             for (final E e : item) {
                 result[offset++] = e;
             }
         }
         if (result.length > size) {
             result[size] = null;
         }
         return (T[]) result;
     }
 
     /**
      * Returns a new Set containing all of the elements.
      *
      * @return A new HashSet containing all of the elements in this composite.
      *   The new collection is <i>not</i> backed by this composite.
      */
     public Set<E> toSet() {
         return new HashSet<>(this);
     }
 }