/*
 * 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.samza.task;

import com.google.common.base.Preconditions;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.ExecutorService;
import org.apache.samza.SamzaException;
import org.apache.samza.context.Context;
import org.apache.samza.operators.OperatorSpecGraph;
import org.apache.samza.operators.impl.InputOperatorImpl;
import org.apache.samza.operators.impl.OperatorImplGraph;
import org.apache.samza.system.EndOfStreamMessage;
import org.apache.samza.system.IncomingMessageEnvelope;
import org.apache.samza.system.MessageType;
import org.apache.samza.system.SystemStream;
import org.apache.samza.system.WatermarkMessage;
import org.apache.samza.util.Clock;
import org.apache.samza.util.SystemClock;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * A {@link StreamTask} implementation that brings all the operator API implementation components together and
 * feeds the input messages into the user-defined transformation chains in {@link OperatorSpecGraph}.
 */
public class StreamOperatorTask implements AsyncStreamTask, InitableTask, WindowableTask, ClosableTask {
  private static final Logger LOG = LoggerFactory.getLogger(StreamOperatorTask.class);

  private final OperatorSpecGraph specGraph;
  private final Clock clock;

  /*
   * Thread pool used by the task to schedule processing of incoming messages. If job.container.thread.pool.size is
   * not configured, this will be null. We don't want to create an executor service within StreamOperatorTask due to
   * following reasons
   *   1. It is harder to reason about the lifecycle of the executor service
   *   2. We end up with thread pool proliferation. Especially for jobs with high number of tasks.
   */
  private ExecutorService taskThreadPool;
  private OperatorImplGraph operatorImplGraph;

  /**
   * Constructs an adaptor task to run the user-implemented {@link OperatorSpecGraph}.
   * @param specGraph the serialized version of user-implemented {@link OperatorSpecGraph}
   *                  that includes the logical DAG
   * @param clock the {@link Clock} to use for time-keeping
   */
  public StreamOperatorTask(OperatorSpecGraph specGraph, Clock clock) {
    this.specGraph = specGraph.clone();
    this.clock = clock;
  }

  public StreamOperatorTask(OperatorSpecGraph specGraph) {
    this(specGraph, SystemClock.instance());
  }

  /**
   * Initializes this task during startup.
   * <p>
   * Implementation: Initializes the runtime {@link OperatorImplGraph} according to user-defined {@link OperatorSpecGraph}.
   * Users set the input and output streams and the task-wide context manager using
   * {@link org.apache.samza.application.descriptors.StreamApplicationDescriptor} APIs, and the logical transforms
   * using the {@link org.apache.samza.operators.MessageStream} APIs. After the
   * {@link org.apache.samza.application.descriptors.StreamApplicationDescriptorImpl} is initialized once by the
   * application, it then creates an immutable {@link OperatorSpecGraph} accordingly, which is passed in to this
   * class to create the {@link OperatorImplGraph} corresponding to the logical DAG.
   *
   * @param context allows initializing and accessing contextual data of this StreamTask
   * @throws Exception in case of initialization errors
   */
  @Override
  public final void init(Context context) throws Exception {
    // create the operator impl DAG corresponding to the logical operator spec DAG
    this.operatorImplGraph = new OperatorImplGraph(specGraph, context, clock);
  }

  /**
   * Passes the incoming message envelopes along to the {@link InputOperatorImpl} node
   * for the input {@link SystemStream}. It is non-blocking and dispatches the message to the container thread
   * pool. The thread pool size is configured through job.container.thread.pool.size. In the absence of the config,
   * the task executes the DAG on the run loop thread.
   * <p>
   * From then on, each {@link org.apache.samza.operators.impl.OperatorImpl} propagates its transformed output to
   * its chained {@link org.apache.samza.operators.impl.OperatorImpl}s itself.
   *
   * @param ime incoming message envelope to process
   * @param collector the collector to send messages with
   * @param coordinator the coordinator to request commits or shutdown
   * @param callback the task callback handle
   */
  @Override
  public final void processAsync(IncomingMessageEnvelope ime, MessageCollector collector, TaskCoordinator coordinator,
      TaskCallback callback) {
    Runnable processRunnable = () -> {
      try {
        SystemStream systemStream = ime.getSystemStreamPartition().getSystemStream();
        InputOperatorImpl inputOpImpl = operatorImplGraph.getInputOperator(systemStream);
        if (inputOpImpl != null) {
          CompletionStage<Void> processFuture;
          MessageType messageType = MessageType.of(ime.getMessage());
          switch (messageType) {
            case USER_MESSAGE:
              processFuture = inputOpImpl.onMessageAsync(ime, collector, coordinator);
              break;

            case END_OF_STREAM:
              EndOfStreamMessage eosMessage = (EndOfStreamMessage) ime.getMessage();
              processFuture =
                  inputOpImpl.aggregateEndOfStream(eosMessage, ime.getSystemStreamPartition(), collector, coordinator);
              break;

            case WATERMARK:
              WatermarkMessage watermarkMessage = (WatermarkMessage) ime.getMessage();
              processFuture = inputOpImpl.aggregateWatermark(watermarkMessage, ime.getSystemStreamPartition(), collector,
                  coordinator);
              break;

            default:
              processFuture = failedFuture(new SamzaException("Unknown message type " + messageType + " encountered."));
              break;
          }

          processFuture.whenComplete((val, ex) -> {
            if (ex != null) {
              callback.failure(ex);
            } else {
              callback.complete();
            }
          });
        }
      } catch (Exception e) {
        LOG.error("Failed to process the incoming message due to ", e);
        callback.failure(e);
      }
    };

    if (taskThreadPool != null) {
      LOG.debug("Processing message using thread pool.");
      taskThreadPool.submit(processRunnable);
    } else {
      LOG.debug("Processing message on the run loop thread.");
      processRunnable.run();
    }
  }

  @Override
  public final void window(MessageCollector collector, TaskCoordinator coordinator)  {
    CompletableFuture<Void> windowFuture = CompletableFuture.allOf(operatorImplGraph.getAllInputOperators()
        .stream()
        .map(inputOperator -> inputOperator.onTimer(collector, coordinator))
        .toArray(CompletableFuture[]::new));

    windowFuture.join();
  }

  @Override
  public void close() throws Exception {
    if (operatorImplGraph != null) {
      operatorImplGraph.close();
    }
  }

  /* package private setter for TaskFactoryUtil to initialize the taskThreadPool */
  void setTaskThreadPool(ExecutorService taskThreadPool) {
    this.taskThreadPool = taskThreadPool;
  }

  /* package private for testing */
  OperatorImplGraph getOperatorImplGraph() {
    return this.operatorImplGraph;
  }

  private static CompletableFuture<Void> failedFuture(Throwable ex) {
    Preconditions.checkNotNull(ex);
    CompletableFuture<Void> failedFuture = new CompletableFuture<>();
    failedFuture.completeExceptionally(ex);

    return failedFuture;
  }
}