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/*
 * Copyright 2014 the original author or authors.
 *
 * 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 ratpack.stream.internal;

import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import ratpack.func.Function;
import ratpack.stream.TransformablePublisher;

import java.time.Duration;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Note, this publisher does not respect back pressure.
 * Must be used in conjunction with a throttling strategy.
 */
public class PeriodicPublisher implements TransformablePublisher {
  private final ScheduledExecutorService executorService;
  private final Function producer;
  private final Duration duration;

  public PeriodicPublisher(ScheduledExecutorService executorService, Function producer, Duration duration) {
    this.executorService = executorService;
    this.producer = producer;
    this.duration = duration;
  }

  @Override
  public void subscribe(final Subscriber s) {
    s.onSubscribe(new PeriodicSubscription(s));
  }

  private class PeriodicSubscription implements Subscription {
    private final AtomicInteger counter;
    private final ScheduledFuture future;
    private Subscriber s;

    public PeriodicSubscription(Subscriber subscription) {
      this.s = subscription;
      counter = new AtomicInteger(0);
      future = executorService.scheduleWithFixedDelay(this::run, 0, duration.toNanos(), TimeUnit.NANOSECONDS);
    }

    private void run() {
      int i = counter.getAndIncrement();
      T value;
      try {
        value = producer.apply(i);
      } catch (Exception e) {
        s.onError(e);
        cancel();
        return;
      }

      if (value == null) {
        s.onComplete();
        cancel();
      } else {
        s.onNext(value);
      }
    }

    @Override
    public void request(long n) {

    }

    @Override
    public void cancel() {
      future.cancel(false);
      s = null;
    }

  }
}