// Copyright 2016 Google Inc. All Rights Reserved.
package com.android.contacts.util.concurrent;

import android.os.Handler;

import com.google.common.util.concurrent.FutureFallback;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;

import java.util.concurrent.CancellationException;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Has utility methods for operating on ListenableFutures
 */
public class FuturesUtil {

    /**
     * See
     * {@link FuturesUtil#withTimeout(ListenableFuture, long, TimeUnit, ScheduledExecutorService)}
     */
    public static <V> ListenableFuture<V> withTimeout(final ListenableFuture<V> future, long time,
            TimeUnit unit, Handler handler) {
        return withTimeout(future, time, unit, ContactsExecutors.newHandlerExecutor(handler));
    }

    /**
     * Returns a future that completes with the result from the input future unless the specified
     * time elapses before it finishes in which case the result will contain a TimeoutException and
     * the input future will be canceled.
     *
     * <p>Guava has Futures.withTimeout but it isn't available until v19.0 and we depend on v14.0
     * right now. Replace usages of this method if we upgrade our dependency.</p>
     */
    public static <V> ListenableFuture<V> withTimeout(final ListenableFuture<V> future, long time,
            TimeUnit unit, ScheduledExecutorService executor) {
        final AtomicBoolean didTimeout = new AtomicBoolean(false);
        executor.schedule(new Runnable() {
            @Override
            public void run() {
                didTimeout.set(!future.isDone() && !future.isCancelled());
                future.cancel(true);
            }
        }, time, unit);

        return Futures.withFallback(future, new FutureFallback<V>() {
            @Override
            public ListenableFuture<V> create(Throwable t) throws Exception {
                if ((t instanceof CancellationException) && didTimeout.get()) {
                    return Futures.immediateFailedFuture(new TimeoutException("Timeout expired"));
                }
                return Futures.immediateFailedFuture(t);
            }
        });
    }
}