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Special Java 1.8+ Library with extended collection related functionality
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/**
 * Copyright (C) 2014-2020 Philip Helger (www.helger.com)
 * philip[at]helger[dot]com
 *
 * Licensed 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 com.helger.collection.multimap;

import java.util.Collection;
import java.util.Map;
import java.util.function.BiConsumer;
import java.util.function.Consumer;

import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import com.helger.commons.annotation.ReturnsMutableObject;
import com.helger.commons.collection.impl.ICommonsCollection;
import com.helger.commons.collection.impl.ICommonsMap;
import com.helger.commons.state.EChange;

/**
 * Base interface for a multi map (one key with several values).
 *
 * @author Philip Helger
 * @param 
 *        Key type
 * @param 
 *        Element type
 * @param 
 *        Container type containing value types
 */
public interface IMultiMap > extends
                           ICommonsMap 
{
  /**
   * Get or create the collection of the specified key.
   *
   * @param aKey
   *        The key to use. May not be null.
   * @return The mutable collection to be used. Never null.
   */
  @Nonnull
  @ReturnsMutableObject ("design")
  COLLTYPE getOrCreate (@Nonnull KEYTYPE aKey);

  /**
   * Add a single value into the container identified by the passed key.
   *
   * @param aKey
   *        The key to use. May not be null.
   * @param aValue
   *        The value to be added. May be null.
   * @return {@link EChange}
   */
  @Nonnull
  default EChange putSingle (@Nonnull final KEYTYPE aKey, @Nullable final VALUETYPE aValue)
  {
    return getOrCreate (aKey).addObject (aValue);
  }

  /**
   * Add all values into the container identified by the passed key-value-map.
   *
   * @param aMap
   *        The key-value-map to use. May not be null.
   * @return {@link EChange}
   */
  @Nonnull
  default EChange putAllIn (@Nonnull final Map  aMap)
  {
    EChange eChange = EChange.UNCHANGED;
    for (final Map.Entry  aEntry : aMap.entrySet ())
      eChange = eChange.or (putSingle (aEntry.getKey (), aEntry.getValue ()));
    return eChange;
  }

  /**
   * Remove a single element from the container identified by the passed key.
   *
   * @param aKey
   *        The key to use. May not be null.
   * @param aValue
   *        The value to be removed. May be null.
   * @return {@link EChange}
   */
  @Nonnull
  default EChange removeSingle (@Nonnull final KEYTYPE aKey, @Nullable final VALUETYPE aValue)
  {
    final COLLTYPE aCont = get (aKey);
    return aCont == null ? EChange.UNCHANGED : aCont.removeObject (aValue);
  }

  /**
   * Check a single element from the container identified by the passed key is
   * present.
   *
   * @param aKey
   *        The key to use. May not be null.
   * @param aValue
   *        The value to be checked. May be null.
   * @return true if the value is contained, false
   *         otherwise
   */
  default boolean containsSingle (@Nonnull final KEYTYPE aKey, @Nullable final VALUETYPE aValue)
  {
    final COLLTYPE aCont = get (aKey);
    return aCont != null && aCont.contains (aValue);
  }

  /**
   * @return The total number of contained values recursively over all contained
   *         maps. Always ≥ 0.
   */
  @Nonnegative
  default long getTotalValueCount ()
  {
    long ret = 0;
    for (final Collection  aChild : values ())
      ret += aChild.size ();
    return ret;
  }

  default void forEachSingle (@Nonnull final BiConsumer  aConsumer)
  {
    for (final Map.Entry  aEntry : entrySet ())
    {
      final KEYTYPE aKey = aEntry.getKey ();
      for (final VALUETYPE aValue : aEntry.getValue ())
        aConsumer.accept (aKey, aValue);
    }
  }

  default void forEachSingleValue (@Nonnull final Consumer  aConsumer)
  {
    for (final Map.Entry  aEntry : entrySet ())
      for (final VALUETYPE aValue : aEntry.getValue ())
        aConsumer.accept (aValue);
  }
}