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/*
 * Copyright (c) 2018 Uber Technologies, Inc. ([email protected])
 *
 * 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 com.uber.hoodie.common.util.queue;

import com.uber.hoodie.common.util.DefaultSizeEstimator;
import com.uber.hoodie.common.util.SizeEstimator;
import com.uber.hoodie.exception.HoodieException;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.function.Function;
import java.util.stream.Collectors;
import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;

/**
 * Executor which orchestrates concurrent producers and consumers communicating through a bounded in-memory queue.
 * This class takes as input the size limit, queue producer(s), consumer and transformer
 * and exposes API to orchestrate concurrent execution of these actors communicating through a central bounded queue
 */
public class BoundedInMemoryExecutor {

  private static Logger logger = LogManager.getLogger(BoundedInMemoryExecutor.class);

  // Executor service used for launching writer thread.
  private final ExecutorService executorService;
  // Used for buffering records which is controlled by HoodieWriteConfig#WRITE_BUFFER_LIMIT_BYTES.
  private final BoundedInMemoryQueue queue;
  // Producers
  private final List> producers;
  // Consumer
  private final Optional> consumer;

  public BoundedInMemoryExecutor(final long bufferLimitInBytes,
      BoundedInMemoryQueueProducer producer,
      Optional> consumer,
      final Function transformFunction) {
    this(bufferLimitInBytes, Arrays.asList(producer), consumer, transformFunction, new DefaultSizeEstimator<>());
  }

  public BoundedInMemoryExecutor(final long bufferLimitInBytes,
      List> producers,
      Optional> consumer,
      final Function transformFunction,
      final SizeEstimator sizeEstimator) {
    this.producers = producers;
    this.consumer = consumer;
    // Ensure single thread for each producer thread and one for consumer
    this.executorService = Executors.newFixedThreadPool(producers.size() + 1);
    this.queue = new BoundedInMemoryQueue<>(bufferLimitInBytes, transformFunction, sizeEstimator);
  }

  /**
   * Callback to implement environment specific behavior before executors (producers/consumer)
   * run.
   */
  public void preExecute() {
    // Do Nothing in general context
  }

  /**
   * Start all Producers
   */
  public ExecutorCompletionService startProducers() {
    // Latch to control when and which producer thread will close the queue
    final CountDownLatch latch = new CountDownLatch(producers.size());
    final ExecutorCompletionService completionService =
        new ExecutorCompletionService(executorService);
    producers.stream().map(producer -> {
      return completionService.submit(() -> {
        try {
          preExecute();
          producer.produce(queue);
        } catch (Exception e) {
          logger.error("error producing records", e);
          queue.markAsFailed(e);
          throw e;
        } finally {
          synchronized (latch) {
            latch.countDown();
            if (latch.getCount() == 0) {
              // Mark production as done so that consumer will be able to exit
              queue.close();
            }
          }
        }
        return true;
      });
    }).collect(Collectors.toList());
    return completionService;
  }

  /**
   * Start only consumer
   */
  private Future startConsumer() {
    return consumer.map(consumer -> {
      return executorService.submit(
          () -> {
            logger.info("starting consumer thread");
            preExecute();
            try {
              E result = consumer.consume(queue);
              logger.info("Queue Consumption is done; notifying producer threads");
              return result;
            } catch (Exception e) {
              logger.error("error consuming records", e);
              queue.markAsFailed(e);
              throw e;
            }
          });
    }).orElse(CompletableFuture.completedFuture(null));
  }

  /**
   * Main API to run both production and consumption
   */
  public E execute() {
    try {
      ExecutorCompletionService producerService = startProducers();
      Future future = startConsumer();
      // Wait for consumer to be done
      return future.get();
    } catch (Exception e) {
      throw new HoodieException(e);
    }
  }


  public boolean isRemaining() {
    return queue.iterator().hasNext();
  }

  public void shutdownNow() {
    executorService.shutdownNow();
  }

  public BoundedInMemoryQueue getQueue() {
    return queue;
  }
}