org.finos.tracdap.common.async.flow.FutureFirstItemSubscriber Maven / Gradle / Ivy

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TRAC D.A.P. data library, interfaces and core functionality for working with primary data

There is a newer version: 0.7.0

/*
 * Copyright 2023 Accenture Global Solutions Limited
 *
 * 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 org.finos.tracdap.common.async.flow;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionException;
import java.util.concurrent.Flow;

public class FutureFirstItemSubscriber implements Flow.Subscriber {

    private final CompletableFuture firstFuture;
    private Flow.Subscription subscription;

    public FutureFirstItemSubscriber(CompletableFuture firstFuture) {
        this.firstFuture = firstFuture;
    }

    @Override
    public void onSubscribe(Flow.Subscription subscription) {
        this.subscription = subscription;
        subscription.request(1);
    }

    @Override
    public void onNext(T item) {
        firstFuture.complete(item);
        subscription.cancel();
    }

    @Override
    public void onError(Throwable error) {

        if (!firstFuture.isDone()) {

            var completionError = (error instanceof CompletionException)
                    ? error : new CompletionException(error.getMessage(), error);

            firstFuture.completeExceptionally(completionError);
        }
    }

    @Override
    public void onComplete() {

        if (!firstFuture.isDone())
            firstFuture.completeExceptionally(new IllegalStateException());
    }
}