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/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2016 DiffPlug.
 *
 * 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.diffplug.common.util.concurrent;

import static com.diffplug.common.base.Preconditions.checkState;

import java.util.List;
import java.util.Optional;

import javax.annotation.Nullable;

import com.google.j2objc.annotations.WeakOuter;

import com.diffplug.common.annotations.GwtCompatible;
import com.diffplug.common.collect.ImmutableCollection;
import com.diffplug.common.collect.ImmutableList;
import com.diffplug.common.collect.Lists;

/**
 * Aggregate future that collects (stores) results of each future.
 */
@GwtCompatible
abstract class CollectionFuture extends AggregateFuture {

	@WeakOuter
	abstract class CollectionFutureRunningState extends RunningState {
		private List> values;

		CollectionFutureRunningState(
				ImmutableCollection> futures,
				boolean allMustSucceed) {
			super(futures, allMustSucceed, true);

			this.values = futures.isEmpty() ? ImmutableList.> of()
					: Lists.> newArrayListWithCapacity(futures.size());

			// Populate the results list with null initially.
			for (int i = 0; i < futures.size(); ++i) {
				values.add(null);
			}
		}

		@Override
		final void collectOneValue(boolean allMustSucceed, int index, @Nullable V returnValue) {
			List> localValues = values;

			if (localValues != null) {
				localValues.set(index, Optional.ofNullable(returnValue));
			} else {
				// Some other future failed or has been cancelled, causing this one to
				// also be cancelled or have an exception set. This should only happen
				// if allMustSucceed is true or if the output itself has been
				// cancelled.
				checkState(allMustSucceed || isCancelled(),
						"Future was done before all dependencies completed");
			}
		}

		@Override
		final void handleAllCompleted() {
			List> localValues = values;
			if (localValues != null) {
				set(combine(localValues));
			} else {
				checkState(isDone());
			}
		}

		@Override
		void releaseResourcesAfterFailure() {
			super.releaseResourcesAfterFailure();
			this.values = null;
		}

		abstract C combine(List> values);
	}
}