/**
 *  Copyright (C) 2009-2011 Typesafe Inc. <http://www.typesafe.com>
 */

package akka.actor

import akka.util.Duration
import org.jboss.netty.akka.util.{ TimerTask, HashedWheelTimer, Timeout ⇒ HWTimeout }
import akka.event.LoggingAdapter
import akka.dispatch.MessageDispatcher
import java.io.Closeable

//#scheduler
/**
 * An Akka scheduler service. This one needs one special behavior: if
 * Closeable, it MUST execute all outstanding tasks upon .close() in order
 * to properly shutdown all dispatchers.
 *
 * Furthermore, this timer service MUST throw IllegalStateException if it
 * cannot schedule a task. Once scheduled, the task MUST be executed. If
 * executed upon close(), the task may execute before its timeout.
 */
trait Scheduler {
  /**
   * Schedules a message to be sent repeatedly with an initial delay and
   * frequency. E.g. if you would like a message to be sent immediately and
   * thereafter every 500ms you would set delay=Duration.Zero and
   * frequency=Duration(500, TimeUnit.MILLISECONDS)
   *
   * Java & Scala API
   */
  def schedule(
    initialDelay: Duration,
    frequency: Duration,
    receiver: ActorRef,
    message: Any): Cancellable

  /**
   * Schedules a function to be run repeatedly with an initial delay and a
   * frequency. E.g. if you would like the function to be run after 2 seconds
   * and thereafter every 100ms you would set delay = Duration(2, TimeUnit.SECONDS)
   * and frequency = Duration(100, TimeUnit.MILLISECONDS)
   *
   * Scala API
   */
  def schedule(
    initialDelay: Duration, frequency: Duration)(f: ⇒ Unit): Cancellable

  /**
   * Schedules a function to be run repeatedly with an initial delay and
   * a frequency. E.g. if you would like the function to be run after 2
   * seconds and thereafter every 100ms you would set delay = Duration(2,
   * TimeUnit.SECONDS) and frequency = Duration(100, TimeUnit.MILLISECONDS)
   *
   * Java API
   */
  def schedule(
    initialDelay: Duration, frequency: Duration, runnable: Runnable): Cancellable

  /**
   * Schedules a Runnable to be run once with a delay, i.e. a time period that
   * has to pass before the runnable is executed.
   *
   * Java & Scala API
   */
  def scheduleOnce(delay: Duration, runnable: Runnable): Cancellable

  /**
   * Schedules a message to be sent once with a delay, i.e. a time period that has
   * to pass before the message is sent.
   *
   * Java & Scala API
   */
  def scheduleOnce(delay: Duration, receiver: ActorRef, message: Any): Cancellable

  /**
   * Schedules a function to be run once with a delay, i.e. a time period that has
   * to pass before the function is run.
   *
   * Scala API
   */
  def scheduleOnce(delay: Duration)(f: ⇒ Unit): Cancellable
}
//#scheduler

//#cancellable
/**
 * Signifies something that can be cancelled
 * There is no strict guarantee that the implementation is thread-safe,
 * but it should be good practice to make it so.
 */
trait Cancellable {
  /**
   * Cancels this Cancellable
   *
   * Java & Scala API
   */
  def cancel(): Unit

  /**
   * Returns whether this Cancellable has been cancelled
   *
   * Java & Scala API
   */
  def isCancelled: Boolean
}
//#cancellable

/**
 * Scheduled tasks (Runnable and functions) are executed with the supplied dispatcher.
 * Note that dispatcher is by-name parameter, because dispatcher might not be initialized
 * when the scheduler is created.
 *
 * The HashedWheelTimer used by this class MUST throw an IllegalStateException
 * if it does not enqueue a task. Once a task is queued, it MUST be executed or
 * returned from stop().
 */
class DefaultScheduler(hashedWheelTimer: HashedWheelTimer,
                       log: LoggingAdapter,
                       dispatcher: ⇒ MessageDispatcher) extends Scheduler with Closeable {

  def schedule(initialDelay: Duration, delay: Duration, receiver: ActorRef, message: Any): Cancellable = {
    val continuousCancellable = new ContinuousCancellable
    val task = new TimerTask with ContinuousScheduling {
      def run(timeout: HWTimeout) {
        receiver ! message
        // Check if the receiver is still alive and kicking before reschedule the task
        if (receiver.isTerminated) {
          log.debug("Could not reschedule message to be sent because receiving actor has been terminated.")
        } else {
          scheduleNext(timeout, delay, continuousCancellable)
        }
      }
    }
    continuousCancellable.init(hashedWheelTimer.newTimeout(task, initialDelay))
    continuousCancellable
  }

  def schedule(initialDelay: Duration, delay: Duration)(f: ⇒ Unit): Cancellable = {
    val continuousCancellable = new ContinuousCancellable
    val task = new TimerTask with ContinuousScheduling with Runnable {
      def run = f
      def run(timeout: HWTimeout) {
        dispatcher execute this
        scheduleNext(timeout, delay, continuousCancellable)
      }
    }
    continuousCancellable.init(hashedWheelTimer.newTimeout(task, initialDelay))
    continuousCancellable
  }

  def schedule(initialDelay: Duration, delay: Duration, runnable: Runnable): Cancellable = {
    val continuousCancellable = new ContinuousCancellable
    val task = new TimerTask with ContinuousScheduling {
      def run(timeout: HWTimeout) {
        dispatcher.execute(runnable)
        scheduleNext(timeout, delay, continuousCancellable)
      }
    }
    continuousCancellable.init(hashedWheelTimer.newTimeout(task, initialDelay))
    continuousCancellable
  }

  def scheduleOnce(delay: Duration, runnable: Runnable): Cancellable = {
    val task = new TimerTask() {
      def run(timeout: HWTimeout) { dispatcher.execute(runnable) }
    }
    new DefaultCancellable(hashedWheelTimer.newTimeout(task, delay))
  }

  def scheduleOnce(delay: Duration, receiver: ActorRef, message: Any): Cancellable = {
    val task = new TimerTask {
      def run(timeout: HWTimeout) {
        receiver ! message
      }
    }
    new DefaultCancellable(hashedWheelTimer.newTimeout(task, delay))
  }

  def scheduleOnce(delay: Duration)(f: ⇒ Unit): Cancellable = {
    val task = new TimerTask {
      def run(timeout: HWTimeout) {
        dispatcher.execute(new Runnable { def run = f })
      }
    }
    new DefaultCancellable(hashedWheelTimer.newTimeout(task, delay))
  }

  private trait ContinuousScheduling { this: TimerTask ⇒
    def scheduleNext(timeout: HWTimeout, delay: Duration, delegator: ContinuousCancellable) {
      try {
        delegator.swap(timeout.getTimer.newTimeout(this, delay))
      } catch {
        case _: IllegalStateException ⇒ // stop recurring if timer is stopped
      }
    }
  }

  private def execDirectly(t: HWTimeout): Unit = {
    try t.getTask.run(t) catch {
      case e: InterruptedException ⇒ throw e
      case e: Exception            ⇒ log.error(e, "exception while executing timer task")
    }
  }

  def close() = {
    import scala.collection.JavaConverters._
    hashedWheelTimer.stop().asScala foreach execDirectly
  }
}

/**
 * Wrapper of a [[org.jboss.netty.akka.util.Timeout]] that delegates all
 * methods. Needed to be able to cancel continuous tasks,
 * since they create new Timeout for each tick.
 */
private[akka] class ContinuousCancellable extends Cancellable {
  @volatile
  private var delegate: HWTimeout = _
  @volatile
  private var cancelled = false

  private[akka] def init(initialTimeout: HWTimeout): Unit = {
    delegate = initialTimeout
  }

  private[akka] def swap(newTimeout: HWTimeout): Unit = {
    val wasCancelled = isCancelled
    delegate = newTimeout
    if (wasCancelled || isCancelled) cancel()
  }

  def isCancelled(): Boolean = {
    // delegate is initially null, but this object will not be exposed to the world until after init
    cancelled || delegate.isCancelled()
  }

  def cancel(): Unit = {
    // the underlying Timeout will not become cancelled once the task has been started to run,
    // therefore we keep a flag here to make sure that rescheduling doesn't occur when cancelled
    cancelled = true
    // delegate is initially null, but this object will not be exposed to the world until after init
    delegate.cancel()
  }
}

class DefaultCancellable(val timeout: HWTimeout) extends Cancellable {
  def cancel() {
    timeout.cancel()
  }

  def isCancelled: Boolean = {
    timeout.isCancelled
  }
}