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/*
 * 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 org.apache.flink.runtime.concurrent;

import org.apache.flink.annotation.VisibleForTesting;

import javax.annotation.Nonnull;

import java.util.Objects;
import java.util.concurrent.Delayed;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicLong;

import static java.util.concurrent.TimeUnit.NANOSECONDS;

/**
 * Adapter from {@link Future} to {@link ScheduledFuture}. This enriches the basic future with
 * scheduling information.
 *
 * @param  value type of the future.
 */
public class ScheduledFutureAdapter implements ScheduledFuture {

    /** The uid sequence generator. */
    private static final AtomicLong SEQUENCE_GEN = new AtomicLong();

    /** The encapsulated basic future to which execution is delegated. */
    @Nonnull private final Future delegate;

    /** Tie-breaker for {@link #compareTo(Delayed)}. */
    private final long tieBreakerUid;

    /** The time when this is scheduled for execution in nanoseconds. */
    private final long scheduleTimeNanos;

    public ScheduledFutureAdapter(
            @Nonnull Future delegate, long delay, @Nonnull TimeUnit timeUnit) {
        this(
                delegate,
                System.nanoTime() + TimeUnit.NANOSECONDS.convert(delay, timeUnit),
                SEQUENCE_GEN.incrementAndGet());
    }

    @VisibleForTesting
    ScheduledFutureAdapter(
            @Nonnull Future delegate, long scheduleTimeNanos, long tieBreakerUid) {

        this.delegate = delegate;
        this.scheduleTimeNanos = scheduleTimeNanos;
        this.tieBreakerUid = tieBreakerUid;
    }

    @Override
    public long getDelay(@Nonnull TimeUnit unit) {
        return unit.convert(scheduleTimeNanos - System.nanoTime(), TimeUnit.NANOSECONDS);
    }

    @Override
    public int compareTo(@Nonnull Delayed o) {

        if (o == this) {
            return 0;
        }

        // tie breaking for ScheduledFutureAdapter objects
        if (o instanceof ScheduledFutureAdapter) {
            ScheduledFutureAdapter typedOther = (ScheduledFutureAdapter) o;
            int cmp = Long.compare(scheduleTimeNanos, typedOther.scheduleTimeNanos);
            return cmp != 0 ? cmp : Long.compare(tieBreakerUid, typedOther.tieBreakerUid);
        }

        return Long.compare(getDelay(NANOSECONDS), o.getDelay(NANOSECONDS));
    }

    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        return delegate.cancel(mayInterruptIfRunning);
    }

    @Override
    public boolean isCancelled() {
        return delegate.isCancelled();
    }

    @Override
    public boolean isDone() {
        return delegate.isDone();
    }

    @Override
    public V get() throws InterruptedException, ExecutionException {
        return delegate.get();
    }

    @Override
    public V get(long timeout, @Nonnull TimeUnit unit)
            throws InterruptedException, ExecutionException, TimeoutException {
        return delegate.get(timeout, unit);
    }

    @VisibleForTesting
    long getTieBreakerUid() {
        return tieBreakerUid;
    }

    @VisibleForTesting
    long getScheduleTimeNanos() {
        return scheduleTimeNanos;
    }

    @Override
    public boolean equals(Object o) {

        if (this == o) {
            return true;
        }

        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        ScheduledFutureAdapter that = (ScheduledFutureAdapter) o;
        return tieBreakerUid == that.tieBreakerUid && scheduleTimeNanos == that.scheduleTimeNanos;
    }

    @Override
    public int hashCode() {
        return Objects.hash(tieBreakerUid, scheduleTimeNanos);
    }
}