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package org.opentripplanner.framework.collection;

import gnu.trove.map.TLongObjectMap;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;

public class MapUtils {

  public static  void addToMapSet(TLongObjectMap> mapSet, long key, U value) {
    Set set = mapSet.get(key);
    if (set == null) {
      set = new HashSet<>();
      mapSet.put(key, set);
    }
    set.add(value);
  }

  /**
   * Map a collection of objects of type S to a list of type T using the provided
   * mapping function.
   * 
   * Nullsafe: if entities is null, then null is returned.
   */
  public static  List mapToList(Collection entities, Function mapper) {
    return entities == null ? null : entities.stream().map(mapper).collect(Collectors.toList());
  }

  /**
   * Takes a list of maps and returns the union of all of them.
   * 
   * If there are duplicate keys then the one from the later argument overwrites the value in an
   * earlier argument.
   */
  @SafeVarargs
  public static  Map combine(Map... maps) {
    var ret = new HashMap();
    Arrays.stream(maps).forEach(ret::putAll);
    return Map.copyOf(ret);
  }
}