when (NimMajor, NimMinor) < (1, 4):
  {.push raises: [Defect].}
else:
  {.push raises: [].}

import
  std/[options, strutils]
import
  chronicles,
  eth/net/nat,
  stew/results,
  stew/shims/net,
  nativesockets

logScope:
  topics = "nat"

proc setupNat*(natConf, clientId: string,
               tcpPort, udpPort: Port):
               Result[tuple[ip: Option[ValidIpAddress],
                            tcpPort: Option[Port],
                            udpPort: Option[Port]], string]
               {.gcsafe.} =

  let strategy = case natConf.toLowerAscii():
      of "any": NatAny
      of "none": NatNone
      of "upnp": NatUpnp
      of "pmp": NatPmp
      else: NatNone

  var endpoint: tuple[ip: Option[ValidIpAddress], tcpPort: Option[Port], udpPort: Option[Port]]

  if strategy != NatNone:
    let extIp = getExternalIP(strategy)
    if extIP.isSome():
      endpoint.ip = some(ValidIpAddress.init(extIp.get()))
      # RedirectPorts in considered a gcsafety violation
      # because it obtains the address of a non-gcsafe proc?
      var extPorts: Option[(Port, Port)]
      try:
        extPorts = ({.gcsafe.}: redirectPorts(tcpPort = tcpPort,
                                              udpPort = udpPort,
                                              description = clientId))
      except CatchableError:
        # TODO: nat.nim Error: can raise an unlisted exception: Exception. Isolate here for now.
        error "unable to determine external ports"
        extPorts = none((Port, Port))

      if extPorts.isSome():
        let (extTcpPort, extUdpPort) = extPorts.get()
        endpoint.tcpPort = some(extTcpPort)
        endpoint.udpPort = some(extUdpPort)

  else: # NatNone
    if not natConf.startsWith("extip:"):
      return err("not a valid NAT mechanism: " & $natConf)

    try:
      # any required port redirection is assumed to be done by hand
      endpoint.ip = some(ValidIpAddress.init(natConf[6..^1]))
    except ValueError:
      return err("not a valid IP address: " & $natConf[6..^1])

  return ok(endpoint)