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package com.commercetools.sync.commons.utils;

import static java.util.Arrays.asList;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Optional;
import java.util.function.Supplier;
import java.util.stream.Collectors;
import javax.annotation.Nonnull;

public final class OptionalUtils {

  /**
   * Takes a {@link Collection} of {@link Optional}s containing some elements of type {@code T},
   * this method filters out any empty {@link Optional} and returns a new list containing the values
   * of the non-empty optionals.
   *
   * @param optionals the collection of optionals that should be filtered out of empty optionals.
   * @param  The type of the elements in the Optionals in the supplied collection {@code
   *     optionals}.
   * @return a new list containing the values of the non-empty optionals from the supplied {@code
   *     optionals} collection.
   */
  @Nonnull
  public static  List filterEmptyOptionals(@Nonnull final Collection> optionals) {
    return filterEmptyOptionals(optionals, ArrayList::new);
  }

  /**
   * Takes zero or more {@link Optional}s containing some elements of type {@code T}, this method
   * filters out any empty {@link Optional} and returns a new list containing the values of the
   * non-empty optionals.
   *
   * @param optionals zero or more optionals that should be filtered out of empty optionals.
   * @param  The type of the elements in the Optionals in the supplied collection {@code
   *     optionals}.
   * @return a new list containing the values of the non-empty optionals from the supplied {@code
   *     optionals}.
   */
  @Nonnull
  @SafeVarargs
  public static  List filterEmptyOptionals(@Nonnull final Optional... optionals) {
    return filterEmptyOptionals(asList(optionals));
  }

  /**
   * Takes a {@link Collection} of {@link Optional}s containing some elements of type {@code T},
   * this method filters out any empty {@link Optional} and returns a new collection, of a type
   * based on the supplied {@code collectionFactory}, containing the values of the non-empty
   * optionals.
   *
   * @param optionals the collection of optionals that should be filtered out of empty optionals.
   * @param collectionFactory the factory which decided on the type of the returned collection.
   * @param  The type of the elements in the Optionals in the supplied collection {@code
   *     optionals}.
   * @param  The type of the collection that should be returned containing the values of the
   *     non-empty optionals.
   * @return a new collection, of a type based on the supplied {@code collectionFactory}, containing
   *     the values of the non-empty optionals from the supplied {@code optionals} collection.
   */
  @Nonnull
  private static > C filterEmptyOptionals(
      @Nonnull final Collection> optionals,
      @Nonnull final Supplier collectionFactory) {

    return optionals.stream()
        .filter(Optional::isPresent)
        .map(Optional::get)
        .collect(Collectors.toCollection(collectionFactory));
  }

  private OptionalUtils() {}
}