/*
    * 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.multiset;
  
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.lang.reflect.Array;
  import java.util.ConcurrentModificationException;
  import java.util.Iterator;
  import java.util.Map;
  
  import org.apache.commons.collections4.MultiSet;
  import org.apache.commons.collections4.iterators.AbstractIteratorDecorator;
  
  /**
   * Abstract implementation of the {@link MultiSet} interface to simplify the
   * creation of subclass implementations.
   * <p>
   * Subclasses specify a Map implementation to use as the internal storage. The
   * map will be used to map multiset elements to a number; the number represents the
   * number of occurrences of that element in the multiset.
   * </p>
   *
   * @param <E> the type held in the multiset
   * @since 4.1
   */
  public abstract class AbstractMapMultiSet<E> extends AbstractMultiSet<E> {
  
      /**
       * Inner class EntrySetIterator.
       */
      protected static class EntrySetIterator<E> implements Iterator<Entry<E>> {
  
          /** The parent map */
          protected final AbstractMapMultiSet<E> parent;
  
          protected final Iterator<Map.Entry<E, MutableInteger>> decorated;
  
          /** The last returned entry */
          protected Entry<E> last;
  
          /** Whether remove is allowed at present */
          protected boolean canRemove;
  
          /**
           * Constructs a new instance.
           * @param iterator  the iterator to decorate
           * @param parent  the parent multiset
           */
          protected EntrySetIterator(final Iterator<Map.Entry<E, MutableInteger>> iterator,
                                     final AbstractMapMultiSet<E> parent) {
              this.decorated = iterator;
              this.parent = parent;
          }
  
          @Override
          public boolean hasNext() {
              return decorated.hasNext();
          }
  
          @Override
          public Entry<E> next() {
              last = new MultiSetEntry<>(decorated.next());
              canRemove = true;
              return last;
          }
  
          @Override
          public void remove() {
              if (!canRemove) {
                  throw new IllegalStateException("Iterator remove() can only be called once after next()");
              }
              decorated.remove();
              last = null;
              canRemove = false;
          }
      }
      /**
       * Inner class iterator for the MultiSet.
       */
      private static final class MapBasedMultiSetIterator<E> implements Iterator<E> {
          private final AbstractMapMultiSet<E> parent;
          private final Iterator<Map.Entry<E, MutableInteger>> entryIterator;
          private Map.Entry<E, MutableInteger> current;
         private int itemCount;
         private final int mods;
         private boolean canRemove;
 
         /**
          * Constructs a new instance.
          *
          * @param parent the parent multiset
          */
         MapBasedMultiSetIterator(final AbstractMapMultiSet<E> parent) {
             this.parent = parent;
             this.entryIterator = parent.map.entrySet().iterator();
             this.current = null;
             this.mods = parent.modCount;
             this.canRemove = false;
         }
 
         /** {@inheritDoc} */
         @Override
         public boolean hasNext() {
             return itemCount > 0 || entryIterator.hasNext();
         }
 
         /** {@inheritDoc} */
         @Override
         public E next() {
             if (parent.modCount != mods) {
                 throw new ConcurrentModificationException();
             }
             if (itemCount == 0) {
                 current = entryIterator.next();
                 itemCount = current.getValue().value;
             }
             canRemove = true;
             itemCount--;
             return current.getKey();
         }
 
         /** {@inheritDoc} */
         @Override
         public void remove() {
             if (parent.modCount != mods) {
                 throw new ConcurrentModificationException();
             }
             if (!canRemove) {
                 throw new IllegalStateException();
             }
             final MutableInteger mut = current.getValue();
             if (mut.value > 1) {
                 mut.value--;
             } else {
                 entryIterator.remove();
             }
             parent.size--;
             canRemove = false;
         }
     }
     /**
      * Inner class MultiSetEntry.
      */
     protected static class MultiSetEntry<E> extends AbstractEntry<E> {
 
         protected final Map.Entry<E, MutableInteger> parentEntry;
 
         /**
          * Constructs a new instance.
          * @param parentEntry  the entry to decorate
          */
         protected MultiSetEntry(final Map.Entry<E, MutableInteger> parentEntry) {
             this.parentEntry = parentEntry;
         }
 
         @Override
         public int getCount() {
             return parentEntry.getValue().value;
         }
 
         @Override
         public E getElement() {
             return parentEntry.getKey();
         }
     }
 
     /**
      * Mutable integer class for storing the data.
      */
     protected static class MutableInteger {
         /** The value of this mutable. */
         protected int value;
 
         /**
          * Constructs a new instance.
          * @param value the initial value
          */
         MutableInteger(final int value) {
             this.value = value;
         }
 
         @Override
         public boolean equals(final Object obj) {
             if (!(obj instanceof MutableInteger)) {
                 return false;
             }
             return ((MutableInteger) obj).value == value;
         }
 
         @Override
         public int hashCode() {
             return value;
         }
     }
 
     /**
      * Inner class UniqueSetIterator.
      */
     protected static class UniqueSetIterator<E> extends AbstractIteratorDecorator<E> {
 
         /** The parent multiset */
         protected final AbstractMapMultiSet<E> parent;
 
         /** The last returned element */
         protected E lastElement;
 
         /** Whether remove is allowed at present */
         protected boolean canRemove;
 
         /**
          * Constructs a new instance.
          * @param iterator  the iterator to decorate
          * @param parent  the parent multiset
          */
         protected UniqueSetIterator(final Iterator<E> iterator, final AbstractMapMultiSet<E> parent) {
             super(iterator);
             this.parent = parent;
         }
 
         @Override
         public E next() {
             lastElement = super.next();
             canRemove = true;
             return lastElement;
         }
 
         @Override
         public void remove() {
             if (!canRemove) {
                 throw new IllegalStateException("Iterator remove() can only be called once after next()");
             }
             final int count = parent.getCount(lastElement);
             super.remove();
             parent.remove(lastElement, count);
             lastElement = null;
             canRemove = false;
         }
     }
 
     /** The map to use to store the data */
     private transient Map<E, MutableInteger> map;
 
     /** The current total size of the multiset */
     private transient int size;
 
     /** The modification count for fail fast iterators */
     private transient int modCount;
 
     /**
      * Constructor needed for subclass serialisation.
      */
     protected AbstractMapMultiSet() {
     }
 
     /**
      * Constructor that assigns the specified Map as the backing store. The map
      * must be empty and non-null.
      *
      * @param map the map to assign
      */
     protected AbstractMapMultiSet(final Map<E, MutableInteger> map) {
         this.map = map;
     }
 
     @Override
     public int add(final E object, final int occurrences) {
         if (occurrences < 0) {
             throw new IllegalArgumentException("Occurrences must not be negative.");
         }
 
         final MutableInteger mut = map.get(object);
         final int oldCount = mut != null ? mut.value : 0;
 
         if (occurrences > 0) {
             modCount++;
             size += occurrences;
             if (mut == null) {
                 map.put(object, new MutableInteger(occurrences));
             } else {
                 mut.value += occurrences;
             }
         }
         return oldCount;
     }
 
     /**
      * Clears the multiset by clearing the underlying map.
      */
     @Override
     public void clear() {
         modCount++;
         map.clear();
         size = 0;
     }
 
     /**
      * Determines if the multiset contains the given element by checking if the
      * underlying map contains the element as a key.
      *
      * @param object the object to search for
      * @return true if the multiset contains the given element
      */
     @Override
     public boolean contains(final Object object) {
         return map.containsKey(object);
     }
 
     @Override
     protected Iterator<Entry<E>> createEntrySetIterator() {
         return new EntrySetIterator<>(map.entrySet().iterator(), this);
     }
 
     @Override
     protected Iterator<E> createUniqueSetIterator() {
         return new UniqueSetIterator<>(getMap().keySet().iterator(), this);
     }
 
     /**
      * Read the multiset in using a custom routine.
      * @param in the input stream
      * @throws IOException any of the usual I/O related exceptions
      * @throws ClassNotFoundException if the stream contains an object which class can not be loaded
      * @throws ClassCastException if the stream does not contain the correct objects
      */
     @Override
     protected void doReadObject(final ObjectInputStream in)
             throws IOException, ClassNotFoundException {
         final int entrySize = in.readInt();
         for (int i = 0; i < entrySize; i++) {
             @SuppressWarnings("unchecked") // This will fail at runtime if the stream is incorrect
             final E obj = (E) in.readObject();
             final int count = in.readInt();
             map.put(obj, new MutableInteger(count));
             size += count;
         }
     }
 
     /**
      * Write the multiset out using a custom routine.
      * @param out the output stream
      * @throws IOException any of the usual I/O related exceptions
      */
     @Override
     protected void doWriteObject(final ObjectOutputStream out) throws IOException {
         out.writeInt(map.size());
         for (final Map.Entry<E, MutableInteger> entry : map.entrySet()) {
             out.writeObject(entry.getKey());
             out.writeInt(entry.getValue().value);
         }
     }
 
     @Override
     public boolean equals(final Object object) {
         if (object == this) {
             return true;
         }
         if (!(object instanceof MultiSet)) {
             return false;
         }
         final MultiSet<?> other = (MultiSet<?>) object;
         if (other.size() != size()) {
             return false;
         }
         for (final E element : map.keySet()) {
             if (other.getCount(element) != getCount(element)) {
                 return false;
             }
         }
         return true;
     }
 
     /**
      * Returns the number of occurrence of the given element in this multiset by
      * looking up its count in the underlying map.
      *
      * @param object the object to search for
      * @return the number of occurrences of the object, zero if not found
      */
     @Override
     public int getCount(final Object object) {
         final MutableInteger count = map.get(object);
         if (count != null) {
             return count.value;
         }
         return 0;
     }
 
     /**
      * Utility method for implementations to access the map that backs this multiset.
      * Not intended for interactive use outside of subclasses.
      *
      * @return the map being used by the MultiSet
      */
     protected Map<E, MutableInteger> getMap() {
         return map;
     }
 
     @Override
     public int hashCode() {
         int total = 0;
         for (final Map.Entry<E, MutableInteger> entry : map.entrySet()) {
             final E element = entry.getKey();
             final MutableInteger count = entry.getValue();
             total += (element == null ? 0 : element.hashCode()) ^ count.value;
         }
         return total;
     }
 
     /**
      * Returns true if the underlying map is empty.
      *
      * @return true if multiset is empty
      */
     @Override
     public boolean isEmpty() {
         return map.isEmpty();
     }
 
     /**
      * Gets an iterator over the multiset elements. Elements present in the
      * MultiSet more than once will be returned repeatedly.
      *
      * @return the iterator
      */
     @Override
     public Iterator<E> iterator() {
         return new MapBasedMultiSetIterator<>(this);
     }
 
     @Override
     public int remove(final Object object, final int occurrences) {
         if (occurrences < 0) {
             throw new IllegalArgumentException("Occurrences must not be negative.");
         }
 
         final MutableInteger mut = map.get(object);
         if (mut == null) {
             return 0;
         }
         final int oldCount = mut.value;
         if (occurrences > 0) {
             modCount++;
             if (occurrences < mut.value) {
                 mut.value -= occurrences;
                 size -= occurrences;
             } else {
                 map.remove(object);
                 size -= mut.value;
                 mut.value = 0;
             }
         }
         return oldCount;
     }
 
     /**
      * Sets the map being wrapped.
      * <p>
      * <b>NOTE:</b> this method should only be used during deserialization
      *
      * @param map the map to wrap
      */
     protected void setMap(final Map<E, MutableInteger> map) {
         this.map = map;
     }
 
     /**
      * Returns the number of elements in this multiset.
      *
      * @return current size of the multiset
      */
     @Override
     public int size() {
         return size;
     }
 
     /**
      * Returns an array of all of this multiset's elements.
      *
      * @return an array of all of this multiset's elements
      */
     @Override
     public Object[] toArray() {
         final Object[] result = new Object[size()];
         int i = 0;
         for (final Map.Entry<E, MutableInteger> entry : map.entrySet()) {
             final E current = entry.getKey();
             final MutableInteger count = entry.getValue();
             for (int index = count.value; index > 0; index--) {
                 result[i++] = current;
             }
         }
         return result;
     }
 
     /**
      * Returns an array of all of this multiset's elements.
      * If the input array has more elements than are in the multiset,
      * trailing elements will be set to null.
      *
      * @param <T> the type of the array elements
      * @param array the array to populate
      * @return an array of all of this multiset's elements
      * @throws ArrayStoreException if the runtime type of the specified array is not
      *   a supertype of the runtime type of the elements in this list
      * @throws NullPointerException if the specified array is null
      */
     @Override
     public <T> T[] toArray(T[] array) {
         final int size = size();
         if (array.length < size) {
             @SuppressWarnings("unchecked") // safe as both are of type T
             final T[] unchecked = (T[]) Array.newInstance(array.getClass().getComponentType(), size);
             array = unchecked;
         }
 
         int i = 0;
         for (final Map.Entry<E, MutableInteger> entry : map.entrySet()) {
             final E current = entry.getKey();
             final MutableInteger count = entry.getValue();
             for (int index = count.value; index > 0; index--) {
                 // unsafe, will throw ArrayStoreException if types are not compatible, see Javadoc
                 @SuppressWarnings("unchecked")
                 final T unchecked = (T) current;
                 array[i++] = unchecked;
             }
         }
         while (i < array.length) {
             array[i++] = null;
         }
         return array;
     }
 
     @Override
     protected int uniqueElements() {
         return map.size();
     }
 }