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 * Copyright (c) 2016, 2017, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package jdk.incubator.http.internal.common;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.CompletionException;

import java.util.concurrent.CompletionStage;

import java.util.concurrent.Executor;

import java.util.function.BiConsumer;

import java.util.function.Function;

import static java.util.Objects.requireNonNull;

import java.util.concurrent.atomic.AtomicLong;

/*

 * A CompletableFuture which does not allow any obtrusion logic.

 * All methods of CompletionStage return instances of this class.

 */

public final class MinimalFuture<T> extends CompletableFuture<T> {

    @FunctionalInterface

    public interface ExceptionalSupplier<U> {

        U get() throws Throwable;

    }

    final static AtomicLong TOKENS = new AtomicLong();

    final long id;

    public static <U> MinimalFuture<U> completedFuture(U value) {

        MinimalFuture<U> f = new MinimalFuture<>();

        f.complete(value);

        return f;

    }

    public static <U> CompletableFuture<U> failedFuture(Throwable ex) {

        requireNonNull(ex);

        MinimalFuture<U> f = new MinimalFuture<>();

        f.completeExceptionally(ex);

        return f;

    }

    public static <U> CompletableFuture<U> supply(ExceptionalSupplier<U> supplier) {

        CompletableFuture<U> cf = new MinimalFuture<>();

        try {

            U value = supplier.get();

            cf.complete(value);

        } catch (Throwable t) {

            cf.completeExceptionally(t);

        }

        return cf;

    }

    public static <U> CompletableFuture<U> supply(ExceptionalSupplier<U> supplier, Executor executor) {

        CompletableFuture<U> cf = new MinimalFuture<>();

        cf.completeAsync( () -> {

            try {

                return supplier.get();

            } catch (Throwable ex) {

                throw new CompletionException(ex);

            }

        }, executor);

        return cf;

    }

    public MinimalFuture() {

        super();

        this.id = TOKENS.incrementAndGet();

    }

    /**

     * Creates a defensive copy of the given {@code CompletionStage}.

     *

     * <p> Might be useful both for producers and consumers of {@code

     * CompletionStage}s.

     *

     * <p> Producers are protected from possible uncontrolled modifications

     * (cancellation, completion, obtrusion, etc.) as well as from executing

     * unknown potentially lengthy or faulty dependants in the given {@code

     * CompletionStage}'s default execution facility or synchronously.

     *

     * <p> Consumers are protected from some of the aspects of misbehaving

     * implementations (e.g. accepting results, applying functions, running

     * tasks, etc. more than once or escape of a reference to their private

     * executor, etc.) by providing a reliable proxy they use instead.

     *

     * @param src

     *         the {@code CompletionStage} to make a copy from

     * @param executor

     *         the executor used to propagate the completion

     * @param <T>

     *         the type of the {@code CompletionStage}'s result

     *

     * @return a copy of the given stage

     */

    public static <T> MinimalFuture<T> copy(CompletionStage<T> src,

                                            Executor executor) {

        MinimalFuture<T> copy = new MinimalFuture<>();

        BiConsumer<T, Throwable> relay =

                (result, error) -> {

                    if (error != null) {

                        copy.completeExceptionally(error);

                    } else {

                        copy.complete(result);

                    }

                };

        if (src.getClass() == CompletableFuture.class) {

            // No subclasses! Strictly genuine CompletableFuture.

            src.whenCompleteAsync(relay, executor);

            return copy;

        } else {

            // Don't give our executor away to an unknown CS!

            src.whenComplete(relay);

            return (MinimalFuture<T>)

                    copy.thenApplyAsync(Function.identity(), executor);

        }

    }

    public static <U> MinimalFuture<U> newMinimalFuture() {

        return new MinimalFuture<>();

    }

    @Override

    public void obtrudeValue(T value) {

        throw new UnsupportedOperationException();

    }

    @Override

    public void obtrudeException(Throwable ex) {

        throw new UnsupportedOperationException();

    }

    @Override

    public String toString() {

        return super.toString() + " (id=" + id +")";

    }

    public static <U> MinimalFuture<U> of(CompletionStage<U> stage) {

        MinimalFuture<U> cf = newMinimalFuture();

        stage.whenComplete((r,t) -> complete(cf, r, t));

        return cf;

    }

    private static <U> void complete(CompletableFuture<U> cf, U result, Throwable t) {

        if (t == null) {

            cf.complete(result);

        } else {

            cf.completeExceptionally(t);

        }

    }

}