AsyncObserver.java

/*
 * Copyright (c) 2015 Spotify AB.
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.spotify.heroic.async;

import com.spotify.heroic.common.Throwing;
import eu.toolchain.async.AsyncFuture;
import eu.toolchain.async.FutureDone;
import eu.toolchain.async.ResolvableFuture;

import java.util.function.Function;

/**
 * XXX: consider replacing with RxJava at some point.
 *
 * @param <T>
 * @author udoprog
 */
public interface AsyncObserver<T> {
    AsyncFuture<Void> observe(final T value);

    void cancel();

    void fail(Throwable cause);

    void end();

    /**
     * Bind a given future as an observeable. It can also be considered as converting a future into
     * an observable.
     * <p>
     * The end states of the observable will be passed on to the future.
     *
     * @param future
     * @param transform Transforms each observed action into a future. This is equivalent to the
     * {@link #observe(Object)} method.
     * @return An observer bound to the given future.
     */
    static <T> AsyncObserver<T> bind(
        final ResolvableFuture<Void> future, final Function<T, AsyncFuture<Void>> transform
    ) {
        return new AsyncObserver<T>() {
            @Override
            public AsyncFuture<Void> observe(T value) {
                return transform.apply(value);
            }

            @Override
            public void cancel() {
                future.cancel();
            }

            @Override
            public void fail(Throwable cause) {
                future.fail(cause);
            }

            @Override
            public void end() {
                future.resolve(null);
            }
        };
    }

    default AsyncObserver<T> onFinished(Runnable finished) {
        return new AsyncObserver<T>() {
            @Override
            public AsyncFuture<Void> observe(T value) {
                return AsyncObserver.this.observe(value);
            }

            @Override
            public void cancel() {
                Throwing.call(AsyncObserver.this::cancel, finished);
            }

            @Override
            public void fail(Throwable cause) {
                Throwing.call(() -> AsyncObserver.this.fail(cause), finished);
            }

            @Override
            public void end() {
                Throwing.call(AsyncObserver.this::end, finished);
            }
        };
    }

    default FutureDone<Void> onDone() {
        return new FutureDone<Void>() {
            @Override
            public void failed(final Throwable cause) throws Exception {
                fail(cause);
            }

            @Override
            public void cancelled() throws Exception {
                cancel();
            }

            @Override
            public void resolved(final Void result) throws Exception {
                end();
            }
        };
    }
}