/*
 * Copyright (c) MuleSoft, Inc.  All rights reserved.  http://www.mulesoft.com
 * The software in this package is published under the terms of the CPAL v1.0
 * license, a copy of which has been included with this distribution in the
 * LICENSE.txt file.
 */
package org.mule.runtime.core.processor.strategy;

import static java.util.Objects.requireNonNull;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static org.mule.runtime.core.processor.strategy.AbstractStreamProcessingStrategyFactory.AbstractStreamProcessingStrategy.WaitStrategy.LITE_BLOCKING;
import static org.mule.runtime.core.processor.strategy.AbstractStreamProcessingStrategyFactory.AbstractStreamProcessingStrategy.WaitStrategy.valueOf;
import static reactor.util.concurrent.QueueSupplier.SMALL_BUFFER_SIZE;
import static reactor.util.concurrent.QueueSupplier.isPowerOfTwo;
import static reactor.util.concurrent.WaitStrategy.blocking;
import static reactor.util.concurrent.WaitStrategy.busySpin;
import static reactor.util.concurrent.WaitStrategy.liteBlocking;
import static reactor.util.concurrent.WaitStrategy.parking;
import static reactor.util.concurrent.WaitStrategy.phasedOffLiteLock;
import static reactor.util.concurrent.WaitStrategy.sleeping;
import static reactor.util.concurrent.WaitStrategy.yielding;

import org.mule.runtime.api.scheduler.Scheduler;
import org.mule.runtime.core.api.Event;
import org.mule.runtime.core.api.construct.FlowConstruct;
import org.mule.runtime.core.api.processor.ReactiveProcessor;
import org.mule.runtime.core.api.processor.Sink;
import org.mule.runtime.core.api.processor.strategy.ProcessingStrategy;
import org.mule.runtime.core.api.processor.strategy.ProcessingStrategyFactory;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Supplier;

import reactor.core.Disposable;
import reactor.core.publisher.WorkQueueProcessor;

/**
 * Abstract {@link ProcessingStrategyFactory} to be used by implementations that de-multiplex incoming messages using a
 * ring-buffer which can then be subscribed to n times.
 * <p/>
 * Processing strategies created with this factory are not suitable for transactional flows and will fail if used with an active
 * transaction.
 *
 * @since 4.0
 */
abstract class AbstractStreamProcessingStrategyFactory extends AbstractProcessingStrategyFactory {

  public static final int DEFAULT_BUFFER_SIZE = SMALL_BUFFER_SIZE;
  public static final int DEFAULT_SUBSCRIBER_COUNT = 1;
  public static final String DEFAULT_WAIT_STRATEGY = LITE_BLOCKING.name();
  protected static String RING_BUFFER_SCHEDULER_NAME_SUFFIX = ".ring-buffer";
  private int bufferSize = DEFAULT_BUFFER_SIZE;
  private int subscriberCount = DEFAULT_SUBSCRIBER_COUNT;
  private String waitStrategy = DEFAULT_WAIT_STRATEGY;

  /**
   * Configure the size of the ring-buffer size used to buffer and de-multiplexes events from multiple source threads. This value
   * must be a power-of two.
   * <p/>
   * Ring buffers typically use a power of two because it means that the rollover at the end of the buffer can be achieved using a
   * bit mask rather than having to explicitly compare the head/tail pointer with the end of the buffer.
   *
   * @param bufferSize buffer size to use.
   */
  public void setBufferSize(int bufferSize) {
    if (!isPowerOfTwo(bufferSize)) {
      throw new IllegalArgumentException("bufferSize must be a power of 2 : " + bufferSize);
    }
    this.bufferSize = bufferSize;
  }

  /**
   * Configure the number of ring-buffer subscribers.
   *
   * @param subscriberCount
   */
  public void setSubscriberCount(int subscriberCount) {
    this.subscriberCount = subscriberCount;
  }

  /**
   * Configure the wait strategy used to wait for new events on ring-buffer.
   *
   * @param waitStrategy
   */
  public void setWaitStrategy(String waitStrategy) {
    this.waitStrategy = waitStrategy;
  }

  protected int getBufferSize() {
    return bufferSize;
  }

  protected int getSubscriberCount() {
    return subscriberCount;
  }

  protected String getWaitStrategy() {
    return waitStrategy;
  }

  /**
   * Abstract {@link ProcessingStrategy} to be used by implementations that de-multiplex incoming messages using a ring-buffer
   * which can then be subscribed to n times.
   * <p/>
   * This processing strategy is not suitable for transactional flows and will fail if used with an active transaction.
   *
   * @since 4.0
   */
  protected abstract static class AbstractStreamProcessingStrategy extends AbstractProcessingStrategy {

    final protected Supplier<Scheduler> ringBufferSchedulerSupplier;
    final protected int bufferSize;
    final protected int subscribers;
    final protected WaitStrategy waitStrategy;
    final protected int maxConcurrency;

    public AbstractStreamProcessingStrategy(Supplier<Scheduler> ringBufferSchedulerSupplier, int bufferSize, int subscribers,
                                            String waitStrategy,
                                            int maxConcurrency) {
      this.subscribers = requireNonNull(subscribers);
      this.waitStrategy = valueOf(waitStrategy);
      this.bufferSize = requireNonNull(bufferSize);
      this.ringBufferSchedulerSupplier = requireNonNull(ringBufferSchedulerSupplier);
      this.maxConcurrency = requireNonNull(maxConcurrency);
    }

    @Override
    public Sink createSink(FlowConstruct flowConstruct, ReactiveProcessor function) {
      WorkQueueProcessor<Event> processor =
          WorkQueueProcessor.share(ringBufferSchedulerSupplier.get(), bufferSize, waitStrategy.getReactorWaitStrategy(), false);
      List<Disposable> disposables = new ArrayList<>();
      for (int i = 0; i < (maxConcurrency < subscribers ? maxConcurrency : subscribers); i++) {
        disposables.add(processor.transform(function).subscribe());
      }
      disposables.add(() -> processor.shutdown());
      return new ReactorSink(processor.connectSink(), () -> disposables.forEach(disposable -> disposable.dispose()),
                             createOnEventConsumer());
    }

    protected enum WaitStrategy {
      BLOCKING(blocking()),

      LITE_BLOCKING(liteBlocking()),

      SLEEPING(sleeping()),

      BUSY_SPIN(busySpin()),

      YIELDING(yielding()),

      PARKING(parking()),

      PHASED(phasedOffLiteLock(200, 100, MILLISECONDS));

      private reactor.util.concurrent.WaitStrategy reactorWaitStrategy;

      WaitStrategy(reactor.util.concurrent.WaitStrategy reactorWaitStrategy) {
        this.reactorWaitStrategy = reactorWaitStrategy;
      }

      reactor.util.concurrent.WaitStrategy getReactorWaitStrategy() {
        return reactorWaitStrategy;
      }
    }

  }
}