/*
    * Portions of this software was developed by employees of the National Institute
    * of Standards and Technology (NIST), an agency of the Federal Government and is
    * being made available as a public service. Pursuant to title 17 United States
    * Code Section 105, works of NIST employees are not subject to copyright
    * protection in the United States. This software may be subject to foreign
    * copyright. Permission in the United States and in foreign countries, to the
    * extent that NIST may hold copyright, to use, copy, modify, create derivative
    * works, and distribute this software and its documentation without fee is hereby
   * granted on a non-exclusive basis, provided that this notice and disclaimer
   * of warranty appears in all copies.
   *
   * THE SOFTWARE IS PROVIDED 'AS IS' WITHOUT ANY WARRANTY OF ANY KIND, EITHER
   * EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY
   * THAT THE SOFTWARE WILL CONFORM TO SPECIFICATIONS, ANY IMPLIED WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND FREEDOM FROM
   * INFRINGEMENT, AND ANY WARRANTY THAT THE DOCUMENTATION WILL CONFORM TO THE
   * SOFTWARE, OR ANY WARRANTY THAT THE SOFTWARE WILL BE ERROR FREE.  IN NO EVENT
   * SHALL NIST BE LIABLE FOR ANY DAMAGES, INCLUDING, BUT NOT LIMITED TO, DIRECT,
   * INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES, ARISING OUT OF, RESULTING FROM,
   * OR IN ANY WAY CONNECTED WITH THIS SOFTWARE, WHETHER OR NOT BASED UPON WARRANTY,
   * CONTRACT, TORT, OR OTHERWISE, WHETHER OR NOT INJURY WAS SUSTAINED BY PERSONS OR
   * PROPERTY OR OTHERWISE, AND WHETHER OR NOT LOSS WAS SUSTAINED FROM, OR AROSE OUT
   * OF THE RESULTS OF, OR USE OF, THE SOFTWARE OR SERVICES PROVIDED HEREUNDER.
   */
  
  package gov.nist.secauto.metaschema.core.util;
  
  import java.util.HashMap;
  import java.util.LinkedHashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.function.BinaryOperator;
  import java.util.function.Function;
  import java.util.function.Supplier;
  import java.util.stream.Collector;
  import java.util.stream.Collectors;
  import java.util.stream.Stream;
  
  import edu.umd.cs.findbugs.annotations.NonNull;
  
  public final class CustomCollectors {
    private CustomCollectors() {
      // disable
    }
  
    @SuppressWarnings("null")
    @NonNull
    public static <T> Function<T, T> identity() {
      return Function.identity();
    }
  
    public static Collector<CharSequence, ?, String> joiningWithOxfordComma(@NonNull String conjunction) {
      return Collectors.collectingAndThen(Collectors.toList(), withOxfordComma(conjunction));
    }
  
    private static Function<List<CharSequence>, String> withOxfordComma(@NonNull String conjunction) {
      return list -> {
        int size = list.size();
        if (size < 2) {
          return String.join("", list);
        }
        if (size == 2) {
          return String.join(" " + conjunction + " ", list);
        }
        // else there are 3 or more
        int last = size - 1;
        return String.join(", " + conjunction + " ",
            String.join(", ", list.subList(0, last)),
            list.get(last));
      };
    }
  
    /**
     * Produce a new stream with duplicates removed based on the provided
     * {@code keyMapper}. When a duplicate key is encountered, the second item is
     * used. The original sequencing is preserved if the input stream is sequential.
     *
     * @param <V>
     *          the item value for the streams
     * @param <K>
     *          the key type
     * @param stream
     *          the stream to reduce
     * @param keyMapper
     *          the key function to use to find unique items
     * @return a new stream
     */
    public static <V, K> Stream<V> distinctByKey(
        @NonNull Stream<V> stream,
        @NonNull Function<? super V, ? extends K> keyMapper) {
      return distinctByKey(stream, keyMapper, (key, value1, value2) -> value2);
    }
  
    /**
     * Produce a new stream with duplicates removed based on the provided
     * {@code keyMapper}. When a duplicate key is encountered, the provided
     * {@code duplicateHandler} is used to determine which item to keep. The
    * original sequencing is preserved if the input stream is sequential.
    *
    * @param <V>
    *          the item value for the streams
    * @param <K>
    *          the key type
    * @param stream
    *          the stream to reduce
    * @param keyMapper
    *          the key function to use to find unique items
    * @param duplicateHander
    *          used to determine which of two duplicates to keep
    * @return a new stream
    */
   public static <V, K> Stream<V> distinctByKey(
       @NonNull Stream<V> stream,
       @NonNull Function<? super V, ? extends K> keyMapper,
       @NonNull DuplicateHandler<K, V> duplicateHander) {
     Map<K, V> uniqueRoles = stream
         .collect(toMap(
             keyMapper,
             identity(),
             duplicateHander,
             LinkedHashMap::new));
     return uniqueRoles.values().stream();
   }
 
   @NonNull
   public static <T, K, V> Collector<T, ?, Map<K, V>> toMap(
       @NonNull Function<? super T, ? extends K> keyMapper,
       @NonNull Function<? super T, ? extends V> valueMapper,
       @NonNull DuplicateHandler<K, V> duplicateHander) {
     return toMap(keyMapper, valueMapper, duplicateHander, HashMap::new);
   }
 
   @NonNull
   public static <T, K, V, M extends Map<K, V>> Collector<T, ?, M> toMap(
       @NonNull Function<? super T, ? extends K> keyMapper,
       @NonNull Function<? super T, ? extends V> valueMapper,
       @NonNull DuplicateHandler<K, V> duplicateHander,
       Supplier<M> supplier) {
     return ObjectUtils.notNull(
         Collector.of(
             supplier,
             (map, item) -> {
               K key = keyMapper.apply(item);
               V value = Objects.requireNonNull(valueMapper.apply(item));
               V oldValue = map.get(key);
               if (oldValue != null) {
                 value = duplicateHander.handle(key, oldValue, value);
               }
               map.put(key, value);
             },
             (map1, map2) -> {
               map2.forEach((key, value) -> {
                 V oldValue = map1.get(key);
                 V newValue = value;
                 if (oldValue != null) {
                   newValue = duplicateHander.handle(key, oldValue, value);
                 }
                 map1.put(key, newValue);
               });
               return map1;
             }));
   }
 
   @FunctionalInterface
   public interface DuplicateHandler<K, V> {
     @NonNull
     V handle(K key, @NonNull V value1, V value2);
   }
 
   @NonNull
   public static <T> BinaryOperator<T> useFirstMapper() {
     return (value1, value2) -> value1;
   }
 
   @NonNull
   public static <T> BinaryOperator<T> useLastMapper() {
     return (value1, value2) -> value2;
   }
 }