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/*
 * Copyright (c) 2013-2018 Spotify AB
 *
 * 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.spotify.futures;

import com.google.common.base.Function;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Maps;
import com.google.common.util.concurrent.ListenableFuture;
import java.util.List;
import java.util.Map;

/**
 * Contains references to a set of joined future values.
 */
public final class JoinedResults {
  private final Map, Object> futures;

  private JoinedResults(Map, Object> futures) {
    this.futures = futures;
  }

  /**
   * Gets a future value if it was part of the joined future values,
   * else throws an illegal argument exception.
   */
  public  T get(ListenableFuture future) {
    Object value = futures.get(future);
    if (value == Null.INSTANCE) {
      return null;
    } else if (value == null) {
      String message = "Attempt to access future value not part of joined operation";
      throw new IllegalArgumentException(message);
    }
    // Must be of type T since futures is an identity map and future has resolved into this
    // value earlier
    @SuppressWarnings("unchecked")
    T t = (T) value;
    return t;
  }

  static class Transform implements Function, JoinedResults> {
    private final List> futures;

    Transform(List> list) {
      futures = ImmutableList.copyOf(list);
    }

    @Override
    public JoinedResults apply(List