/*
    * 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;
  
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.Set;
  
  /**
   * Defines a collection that counts the number of times an object appears in
   * the collection.
   * <p>
   * Suppose you have a Bag that contains {@code {a, a, b, c}}.
   * Calling {@link #getCount(Object)} on {@code a} would return 2, while
   * calling {@link #uniqueSet()} would return {@code {a, b, c}}.
   * </p>
   * <p>
   * <em>NOTE: This interface violates the {@link Collection} contract.</em>
   * The behavior specified in many of these methods is <em>not</em> the same
   * as the behavior specified by {@code Collection}.
   * The non-compliant methods are clearly marked with "(Violation)".
   * Exercise caution when using a bag as a {@code Collection}.
   * </p>
   * <p>
   * This violation resulted from the original specification of this interface.
   * In an ideal world, the interface would be changed to fix the problems, however
   * it has been decided to maintain backwards compatibility instead.
   * </p>
   *
   * @param <E> the type of elements in this bag
   * @since 2.0
   */
  public interface Bag<E> extends Collection<E> {
  
      /**
       * <em>(Violation)</em>
       * Adds one copy of the specified object to the Bag.
       * <p>
       * If the object is already in the {@link #uniqueSet()} then increment its
       * count as reported by {@link #getCount(Object)}. Otherwise add it to the
       * {@link #uniqueSet()} and report its count as 1.
       * </p>
       * <p>
       * Since this method always increases the size of the bag,
       * according to the {@link Collection#add(Object)} contract, it
       * should always return {@code true}.  Since it sometimes returns
       * {@code false}, this method violates the contract.
       * </p>
       *
       * @param object  the object to add
       * @return {@code true} if the object was not already in the {@code uniqueSet}
       */
      @Override
      boolean add(E object);
  
      /**
       * Adds {@code nCopies} copies of the specified object to the Bag.
       * <p>
       * If the object is already in the {@link #uniqueSet()} then increment its
       * count as reported by {@link #getCount(Object)}. Otherwise add it to the
       * {@link #uniqueSet()} and report its count as {@code nCopies}.
       * </p>
       *
       * @param object  the object to add
       * @param nCopies  the number of copies to add
       * @return {@code true} if the object was not already in the {@code uniqueSet}
       * @throws ClassCastException if the class of the specified element prevents it from being added to this collection
       */
      boolean add(E object, int nCopies);
  
      /**
       * <em>(Violation)</em>
       * Returns {@code true} if the bag contains all elements in
       * the given collection, respecting cardinality.  That is, if the
       * given collection {@code coll} contains {@code n} copies
       * of a given object, calling {@link #getCount(Object)} on that object must
       * be {@code &gt;= n} for all {@code n} in {@code coll}.
       *
       * <p>
       * The {@link Collection#containsAll(Collection)} method specifies
       * that cardinality should <em>not</em> be respected; this method should
       * return true if the bag contains at least one of every object contained
       * in the given collection.
       * </p>
       *
      * @param coll  the collection to check against
      * @return {@code true} if the Bag contains all the collection
      */
     @Override
     boolean containsAll(Collection<?> coll);
 
     /**
      * Returns the number of occurrences (cardinality) of the given
      * object currently in the bag. If the object does not exist in the
      * bag, return 0.
      *
      * @param object  the object to search for
      * @return the number of occurrences of the object, zero if not found
      */
     int getCount(Object object);
 
     /**
      * Returns an {@link Iterator} over the entire set of members,
      * including copies due to cardinality. This iterator is fail-fast
      * and will not tolerate concurrent modifications.
      *
      * @return iterator over all elements in the Bag
      */
     @Override
     Iterator<E> iterator();
 
     /**
      * <em>(Violation)</em>
      * Removes all occurrences of the given object from the bag.
      * <p>
      * This will also remove the object from the {@link #uniqueSet()}.
      * </p>
      * <p>
      * According to the {@link Collection#remove(Object)} method,
      * this method should only remove the <em>first</em> occurrence of the
      * given object, not <em>all</em> occurrences.
      * </p>
      *
      * @param object  the object to remove
      * @return {@code true} if this call changed the collection
      */
     @Override
     boolean remove(Object object);
 
     /**
      * Removes {@code nCopies} copies of the specified object from the Bag.
      * <p>
      * If the number of copies to remove is greater than the actual number of
      * copies in the Bag, no error is thrown.
      * </p>
      *
      * @param object  the object to remove
      * @param nCopies  the number of copies to remove
      * @return {@code true} if this call changed the collection
      */
     boolean remove(Object object, int nCopies);
 
     /**
      * <em>(Violation)</em>
      * Remove all elements represented in the given collection,
      * respecting cardinality.  That is, if the given collection
      * {@code coll} contains {@code n} copies of a given object,
      * the bag will have {@code n} fewer copies, assuming the bag
      * had at least {@code n} copies to begin with.
      *
      * <p>
      * The {@link Collection#removeAll(Collection)} method specifies
      * that cardinality should <em>not</em> be respected; this method should
      * remove <em>all</em> occurrences of every object contained in the
      * given collection.
      * </p>
      *
      * @param coll  the collection to remove
      * @return {@code true} if this call changed the collection
      */
     @Override
     boolean removeAll(Collection<?> coll);
 
     /**
      * <em>(Violation)</em>
      * Remove any members of the bag that are not in the given
      * collection, respecting cardinality.  That is, if the given
      * collection {@code coll} contains {@code n} copies of a
      * given object and the bag has {@code m &gt; n} copies, then
      * delete {@code m - n} copies from the bag.  In addition, if
      * {@code e} is an object in the bag but
      * {@code !coll.contains(e)}, then remove {@code e} and any
      * of its copies.
      *
      * <p>
      * The {@link Collection#retainAll(Collection)} method specifies
      * that cardinality should <em>not</em> be respected; this method should
      * keep <em>all</em> occurrences of every object contained in the
      * given collection.
      * </p>
      *
      * @param coll  the collection to retain
      * @return {@code true} if this call changed the collection
      */
     @Override
     boolean retainAll(Collection<?> coll);
 
     /**
      * Returns the total number of items in the bag across all types.
      *
      * @return the total size of the Bag
      */
     @Override
     int size();
 
     /**
      * Returns a {@link Set} of unique elements in the Bag.
      * <p>
      * Uniqueness constraints are the same as those in {@link java.util.Set}.
      * </p>
      *
      * @return the Set of unique Bag elements
      */
     Set<E> uniqueSet();
 
     // The following is not part of the formal Bag interface, however where possible
     // Bag implementations should follow these comments.
 //    /**
 //     * Compares this Bag to another.
 //     * This Bag equals another Bag if it contains the same number of occurrences of
 //     * the same elements.
 //     * This equals definition is compatible with the Set interface.
 //     *
 //     * @param obj  the Bag to compare to
 //     * @return true if equal
 //     */
 //    boolean equals(Object obj);
 //
 //    /**
 //     * Gets a hash code for the Bag compatible with the definition of equals.
 //     * The hash code is defined as the sum total of a hash code for each element.
 //     * The per element hash code is defined as
 //     * {@code (e==null ? 0 : e.hashCode()) ^ noOccurrences)}.
 //     * This hash code definition is compatible with the Set interface.
 //     *
 //     * @return the hash code of the Bag
 //     */
 //    int hashCode();
 
 }