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Java wrapper for the popular chat & VOIP service: Discord https://discord.com

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/*
 * Copyright 2015 Austin Keener, Michael Ritter, Florian Spieß, and the JDA contributors
 *
 * 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 net.dv8tion.jda.internal.utils;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.util.concurrent.CompletableFuture;
import java.util.function.Function;

public class FutureUtil
{
    @Nonnull
    public static  CompletableFuture thenApplyCancellable(@Nonnull CompletableFuture future, @Nonnull Function applyFunction, @Nullable Runnable onCancel)
    {
        final CompletableFuture cf = new CompletableFuture<>();

        future.thenAccept(t -> cf.complete(applyFunction.apply(t)))
                .exceptionally(throwable ->
                {
                    cf.completeExceptionally(throwable);
                    return null;
                });

        cf.whenComplete((u, throwable) ->
        {
            if (cf.isCancelled())
            {
                future.cancel(true);
                if (onCancel != null)
                    onCancel.run();
            }
        });

        return cf;
    }

    @Nonnull
    public static  CompletableFuture thenApplyCancellable(@Nonnull CompletableFuture future, @Nonnull Function applyFunction)
    {
        return thenApplyCancellable(future, applyFunction, null);
    }
}