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Swirlds is a software platform designed to build fully-distributed applications that harness the power of the cloud without servers. Now you can develop applications with fairness in decision making, speed, trust and reliability, at a fraction of the cost of traditional server-based platforms.

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/*
 * Copyright (C) 2016-2024 Hedera Hashgraph, LLC
 *
 * 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.swirlds.common.merkle.hash;

import com.swirlds.common.crypto.Hash;
import com.swirlds.common.merkle.MerkleNode;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * This future object is used by {@link MerkleHashBuilder#digestTreeAsync(MerkleNode)} to return a hash to the user.
 */
public class FutureMerkleHash implements Future {

    private volatile Hash hash;
    private volatile Throwable exception;
    private final CountDownLatch latch;

    /**
     * Create a future that will eventually have the hash specified.
     */
    public FutureMerkleHash() {
        latch = new CountDownLatch(1);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean cancel(final boolean mayInterruptIfRunning) {
        throw new UnsupportedOperationException();
    }

    /**
     * This method is used to register that an exception was encountered while hashing the tree.
     */
    public synchronized void cancelWithException(final Throwable exception) {
        if (exception != null) {
            // Only the first exception gets rethrown
            this.exception = exception;
            latch.countDown();
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean isCancelled() {
        return exception != null;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean isDone() {
        return hash != null;
    }

    /**
     * If there were any exceptions encountered during hashing, rethrow that exception.
     */
    private void rethrowException() throws ExecutionException {
        if (exception != null) {
            throw new ExecutionException(exception);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Hash get() throws InterruptedException, ExecutionException {
        latch.await();
        rethrowException();
        return hash;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Hash get(final long timeout, final TimeUnit unit)
            throws InterruptedException, TimeoutException, ExecutionException {
        if (!latch.await(timeout, unit)) {
            throw new TimeoutException();
        }
        rethrowException();
        return hash;
    }

    /**
     * Set the hash for the tree.
     *
     * @param hash
     * 		the hash
     */
    public synchronized void set(Hash hash) {
        if (exception == null) {
            this.hash = hash;
            latch.countDown();
        }
    }
}