/*
 * Copyright (C) 2009-2018 Lightbend Inc. <https://www.lightbend.com>
 */

package akka.io

import java.net.InetSocketAddress
import java.nio.ByteBuffer
import java.nio.channels.DatagramChannel
import java.nio.channels.SelectionKey._
import scala.annotation.tailrec
import scala.util.control.NonFatal
import akka.actor.{ Actor, ActorLogging, ActorRef }
import akka.dispatch.{ UnboundedMessageQueueSemantics, RequiresMessageQueue }
import akka.util.ByteString
import akka.io.SelectionHandler._
import akka.io.UdpConnected._

/**
 * INTERNAL API
 */
private[io] class UdpConnection(
  udpConn:         UdpConnectedExt,
  channelRegistry: ChannelRegistry,
  commander:       ActorRef,
  connect:         Connect)
  extends Actor with ActorLogging with RequiresMessageQueue[UnboundedMessageQueueSemantics] {

  import connect._
  import udpConn._
  import udpConn.settings._

  var pendingSend: (Send, ActorRef) = null
  def writePending = pendingSend ne null

  context.watch(handler) // sign death pact
  var channel: DatagramChannel = null

  if (remoteAddress.isUnresolved) {
    Dns.resolve(remoteAddress.getHostName)(context.system, self) match {
      case Some(r) ⇒
        doConnect(new InetSocketAddress(r.addr, remoteAddress.getPort))
      case None ⇒
        context.become(resolving(), discardOld = true)
    }
  } else {
    doConnect(remoteAddress)
  }

  def resolving(): Receive = {
    case r: Dns.Resolved ⇒
      reportConnectFailure {
        doConnect(new InetSocketAddress(r.addr, remoteAddress.getPort))
      }
  }

  def doConnect(address: InetSocketAddress): Unit = {
    reportConnectFailure {
      channel = DatagramChannel.open
      channel.configureBlocking(false)
      val socket = channel.socket
      options.foreach(_.beforeDatagramBind(socket))
      localAddress foreach socket.bind
      channel.connect(remoteAddress)
      channelRegistry.register(channel, OP_READ)
    }
    log.debug("Successfully connected to [{}]", remoteAddress)
  }

  def receive = {
    case registration: ChannelRegistration ⇒
      options.foreach {
        case v2: Inet.SocketOptionV2 ⇒ v2.afterConnect(channel.socket)
        case _                       ⇒
      }
      commander ! Connected
      context.become(connected(registration), discardOld = true)
  }

  def connected(registration: ChannelRegistration): Receive = {
    case SuspendReading  ⇒ registration.disableInterest(OP_READ)
    case ResumeReading   ⇒ registration.enableInterest(OP_READ)
    case ChannelReadable ⇒ doRead(registration, handler)

    case Disconnect ⇒
      log.debug("Closing UDP connection to [{}]", remoteAddress)
      channel.close()
      sender() ! Disconnected
      log.debug("Connection closed to [{}], stopping listener", remoteAddress)
      context.stop(self)

    case send: Send if writePending ⇒
      if (TraceLogging) log.debug("Dropping write because queue is full")
      sender() ! CommandFailed(send)

    case send: Send if send.payload.isEmpty ⇒
      if (send.wantsAck)
        sender() ! send.ack

    case send: Send ⇒
      pendingSend = (send, sender())
      registration.enableInterest(OP_WRITE)

    case ChannelWritable ⇒ doWrite()
  }

  def doRead(registration: ChannelRegistration, handler: ActorRef): Unit = {
    @tailrec def innerRead(readsLeft: Int, buffer: ByteBuffer): Unit = {
      buffer.clear()
      buffer.limit(DirectBufferSize)

      if (channel.read(buffer) > 0) {
        buffer.flip()
        handler ! Received(ByteString(buffer))
        innerRead(readsLeft - 1, buffer)
      }
    }
    val buffer = bufferPool.acquire()
    try innerRead(BatchReceiveLimit, buffer) finally {
      registration.enableInterest(OP_READ)
      bufferPool.release(buffer)
    }
  }

  final def doWrite(): Unit = {
    val buffer = udpConn.bufferPool.acquire()
    try {
      val (send, commander) = pendingSend
      buffer.clear()
      send.payload.copyToBuffer(buffer)
      buffer.flip()
      val writtenBytes = channel.write(buffer)
      if (TraceLogging) log.debug("Wrote [{}] bytes to channel", writtenBytes)

      // Datagram channel either sends the whole message, or nothing
      if (writtenBytes == 0) commander ! CommandFailed(send)
      else if (send.wantsAck) commander ! send.ack
    } finally {
      udpConn.bufferPool.release(buffer)
      pendingSend = null
    }
  }

  override def postStop(): Unit =
    if (channel.isOpen) {
      log.debug("Closing DatagramChannel after being stopped")
      try channel.close()
      catch {
        case NonFatal(e) ⇒ log.debug("Error closing DatagramChannel: {}", e)
      }
    }

  private def reportConnectFailure(thunk: ⇒ Unit): Unit = {
    try {
      thunk
    } catch {
      case NonFatal(e) ⇒
        log.debug(
          "Failure while connecting UDP channel to remote address [{}] local address [{}]: {}",
          remoteAddress, localAddress.getOrElse("undefined"), e)
        commander ! CommandFailed(connect)
        context.stop(self)
    }
  }
}
