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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.Publisher;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import ratpack.func.Function;

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 Publisher {
  private final ScheduledExecutorService executorService;
  private final Function producer;
  private final long delay;
  private final TimeUnit timeUnit;

  public  PeriodicPublisher(ScheduledExecutorService executorService, Function producer, long delay, TimeUnit timeUnit) {
    this.executorService = executorService;
    this.producer = producer;
    this.delay = delay;
    this.timeUnit = timeUnit;
  }

  @Override
  public void subscribe(final Subscriber s) {
    s.onSubscribe(new Subscription() {
      private final AtomicInteger counter = new AtomicInteger(0);
      private final ScheduledFuture future = executorService.scheduleWithFixedDelay(new Runnable() {
        @Override
        public void run() {
          int i = counter.getAndIncrement();
          T value;
          try {
            value = producer.apply(i);
          } catch (Exception e) {
            future.cancel(false);
            s.onError(e);
            return;
          }

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

      }, 0, delay, timeUnit);

      @Override
      public void request(int n) {

      }

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