/*
 * Copyright (C) 2017-2021 Lightbend Inc. <https://www.lightbend.com>
 */

package akka.actor.typed
package internal

import java.time.Duration

import akka.actor.{ Cancellable, NotInfluenceReceiveTimeout }
import akka.actor.typed.scaladsl.{ ActorContext, LoggerOps }
import akka.annotation.InternalApi
import akka.dispatch.ExecutionContexts
import akka.util.OptionVal
import org.slf4j.Logger

import scala.concurrent.duration.FiniteDuration

/**
 * INTERNAL API
 */
@InternalApi private[akka] object TimerSchedulerImpl {
  final case class Timer[T](key: Any, msg: T, repeat: Boolean, generation: Int, task: Cancellable)
  sealed class TimerMsg(val key: Any, val generation: Int, val owner: AnyRef) {
    override def toString = s"TimerMsg(key=$key, generation=$generation, owner=$owner)"
  }

  def withTimers[T](factory: TimerSchedulerCrossDslSupport[T] => Behavior[T]): Behavior[T] = {
    scaladsl.Behaviors.setup[T](wrapWithTimers(factory))
  }

  def wrapWithTimers[T](factory: TimerSchedulerCrossDslSupport[T] => Behavior[T])(ctx: ActorContext[T]): Behavior[T] =
    ctx match {
      case ctxImpl: ActorContextImpl[T] =>
        val timerScheduler = ctxImpl.timer
        factory(timerScheduler)
      case _ => throw new IllegalArgumentException(s"timers not supported with [${ctx.getClass}]")
    }

  private sealed trait TimerMode {
    def repeat: Boolean
  }
  private case class FixedRateMode(initialDelay: FiniteDuration) extends TimerMode {
    override def repeat: Boolean = true
  }
  private case class FixedDelayMode(initialDelay: FiniteDuration) extends TimerMode {
    override def repeat: Boolean = true
  }
  private case object SingleMode extends TimerMode {
    override def repeat: Boolean = false
  }
}

@InternalApi private[akka] trait TimerSchedulerCrossDslSupport[T]
    extends scaladsl.TimerScheduler[T]
    with javadsl.TimerScheduler[T] {
  import akka.util.JavaDurationConverters._

  override final def startTimerWithFixedDelay(key: Any, msg: T, delay: Duration): Unit =
    startTimerWithFixedDelay(key, msg, delay.asScala)

  override final def startTimerWithFixedDelay(key: Any, msg: T, initialDelay: Duration, delay: Duration): Unit =
    startTimerWithFixedDelay(key, msg, initialDelay.asScala, delay.asScala)

  override final def startTimerAtFixedRate(key: Any, msg: T, interval: Duration): Unit =
    startTimerAtFixedRate(key, msg, interval.asScala)

  override final def startTimerAtFixedRate(key: Any, msg: T, initialDelay: Duration, interval: Duration): Unit =
    startTimerAtFixedRate(key, msg, initialDelay.asScala, interval.asScala)

  override final def startPeriodicTimer(key: Any, msg: T, interval: Duration): Unit = {
    //this follows the deprecation note in the super class
    startTimerWithFixedDelay(key, msg, interval.asScala)
  }

  override final def startSingleTimer(key: Any, msg: T, delay: Duration): Unit =
    startSingleTimer(key, msg, delay.asScala)
}

/**
 * INTERNAL API
 */
@InternalApi private[akka] class TimerSchedulerImpl[T](ctx: ActorContext[T])
    extends scaladsl.TimerScheduler[T]
    with TimerSchedulerCrossDslSupport[T] {
  import TimerSchedulerImpl._

  private var timers: Map[Any, Timer[T]] = Map.empty
  private val timerGen = Iterator.from(1)

  override def startTimerAtFixedRate(key: Any, msg: T, interval: FiniteDuration): Unit =
    startTimer(key, msg, interval, FixedRateMode(interval))

  override def startTimerAtFixedRate(key: Any, msg: T, initialDelay: FiniteDuration, interval: FiniteDuration): Unit =
    startTimer(key, msg, interval, FixedRateMode(initialDelay))

  override def startTimerWithFixedDelay(key: Any, msg: T, delay: FiniteDuration): Unit =
    startTimer(key, msg, delay, FixedDelayMode(delay))

  override def startTimerWithFixedDelay(key: Any, msg: T, initialDelay: FiniteDuration, delay: FiniteDuration): Unit =
    startTimer(key, msg, delay, FixedDelayMode(initialDelay))

  override def startPeriodicTimer(key: Any, msg: T, interval: FiniteDuration): Unit =
    startTimer(key, msg, interval, FixedRateMode(interval))

  override def startSingleTimer(key: Any, msg: T, delay: FiniteDuration): Unit =
    startTimer(key, msg, delay, SingleMode)

  private def startTimer(key: Any, msg: T, delay: FiniteDuration, mode: TimerMode): Unit = {
    timers.get(key) match {
      case Some(t) => cancelTimer(t)
      case None    =>
    }
    val nextGen = timerGen.next()

    val timerMsg =
      if (msg.isInstanceOf[NotInfluenceReceiveTimeout])
        new TimerMsg(key, nextGen, this) with NotInfluenceReceiveTimeout
      else
        new TimerMsg(key, nextGen, this)

    val task = mode match {
      case SingleMode =>
        ctx.system.scheduler.scheduleOnce(delay, () => ctx.self.unsafeUpcast ! timerMsg)(ExecutionContexts.parasitic)
      case m: FixedDelayMode =>
        ctx.system.scheduler.scheduleWithFixedDelay(m.initialDelay, delay)(() => ctx.self.unsafeUpcast ! timerMsg)(
          ExecutionContexts.parasitic)
      case m: FixedRateMode =>
        ctx.system.scheduler.scheduleAtFixedRate(m.initialDelay, delay)(() => ctx.self.unsafeUpcast ! timerMsg)(
          ExecutionContexts.parasitic)
    }

    val nextTimer = Timer(key, msg, mode.repeat, nextGen, task)
    timers = timers.updated(key, nextTimer)
  }

  override def isTimerActive(key: Any): Boolean =
    timers.contains(key)

  override def cancel(key: Any): Unit = {
    timers.get(key) match {
      case None    => // already removed/canceled
      case Some(t) => cancelTimer(t)
    }
  }

  private def cancelTimer(timer: Timer[T]): Unit = {
    ctx.log.debug("Cancel timer [{}] with generation [{}]", timer.key, timer.generation)
    timer.task.cancel()
    timers -= timer.key
  }

  override def cancelAll(): Unit = {
    ctx.log.debug("Cancel all timers")
    timers.valuesIterator.foreach { timer =>
      timer.task.cancel()
    }
    timers = Map.empty
  }

  def interceptTimerMsg(log: Logger, timerMsg: TimerMsg): OptionVal[T] = {
    timers.get(timerMsg.key) match {
      case None =>
        // it was from canceled timer that was already enqueued in mailbox
        log.debug("Received timer [{}] that has been removed, discarding", timerMsg.key)
        OptionVal.none // message should be ignored
      case Some(t) =>
        if (timerMsg.owner ne this) {
          // after restart, it was from an old instance that was enqueued in mailbox before canceled
          log.debug("Received timer [{}] from old restarted instance, discarding", timerMsg.key)
          OptionVal.none // message should be ignored
        } else if (timerMsg.generation == t.generation) {
          // valid timer
          if (!t.repeat)
            timers -= t.key
          OptionVal.Some(t.msg)
        } else {
          // it was from an old timer that was enqueued in mailbox before canceled
          if (log.isDebugEnabled)
            log.debugN(
              "Received timer [{}] from old generation [{}], expected generation [{}], discarding",
              timerMsg.key,
              timerMsg.generation,
              t.generation)
          OptionVal.none // message should be ignored
        }
    }
  }
}
