/*
 * Copyright (c) 2016, 2020, 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.internal.net.http.common;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.atomic.AtomicLong;

import static java.util.Objects.requireNonNull;

/*
 * 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;
    }

    private final static AtomicLong TOKENS = new AtomicLong();
    private final long id;
    private final Cancelable cancelable;

    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 MinimalFuture() {
        this(null);
    }

    public MinimalFuture(Cancelable cancelable) {
        super();
        this.id = TOKENS.incrementAndGet();
        this.cancelable = cancelable;
    }

    @Override
    public <U> MinimalFuture<U> newIncompleteFuture() {
        return new MinimalFuture<>(cancelable);
    }

    @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 +")";
    }

    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        boolean result = false;
        if  (cancelable != null && !isDone()) {
            result = cancelable.cancel(mayInterruptIfRunning);
        }
        return super.cancel(mayInterruptIfRunning) || result;
    }

    private Cancelable cancelable() {
        return cancelable;
    }

    public static <U> MinimalFuture<U> of(CompletionStage<U> stage) {
        Cancelable cancelable = stage instanceof MinimalFuture
                ? ((MinimalFuture)stage).cancelable() : null;
        MinimalFuture<U> cf = new MinimalFuture<>(cancelable);
        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);
        }
    }
}