# Nim-LibP2P
# Copyright (c) 2022 Status Research & Development GmbH
# Licensed under either of
#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
#  * MIT license ([LICENSE-MIT](LICENSE-MIT))
# at your option.
# This file may not be copied, modified, or distributed except according to
# those terms.

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

import options, sequtils, tables, sugar

import chronos, chronicles

import ./messages,
       ./rconn,
       ./utils,
       ../../peerinfo,
       ../../switch,
       ../../multiaddress,
       ../../multicodec,
       ../../stream/connection,
       ../../protocols/protocol,
       ../../transports/transport,
       ../../errors,
       ../../utils/heartbeat,
       ../../signed_envelope

# TODO:
# * Eventually replace std/times by chronos/timer. Currently chronos/timer
#   doesn't offer the possibility to get a datetime in UNIX UTC
# * Eventually add an access control list in the handleReserve, handleConnect
#   and handleHop
# * Better reservation management ie find a way to re-reserve when the end is nigh

import std/times
export chronicles

const
  RelayMsgSize* = 4096
  DefaultReservationTTL* = initDuration(hours = 1)
  DefaultLimitDuration* = 120
  DefaultLimitData* = 1 shl 17
  DefaultHeartbeatSleepTime* = 1
  MaxCircuit* = 128
  MaxCircuitPerPeer* = 16

logScope:
  topics = "libp2p relay"

type
  RelayV2Error* = object of LPError
  SendStopError = object of RelayV2Error

# Relay Side

type
  Relay* = ref object of LPProtocol
    switch*: Switch
    peerCount: CountTable[PeerId]

    # number of reservation (relayv2) + number of connection (relayv1)
    maxCircuit*: int

    maxCircuitPerPeer*: int
    msgSize*: int
    # RelayV1
    isCircuitRelayV1*: bool
    streamCount: int
    # RelayV2
    rsvp: Table[PeerId, DateTime]
    reservationLoop: Future[void]
    reservationTTL*: times.Duration
    heartbeatSleepTime*: uint32
    limit*: Limit

# Relay V2

proc createReserveResponse(
    r: Relay,
    pid: PeerId,
    expire: DateTime): Result[HopMessage, CryptoError] =
  let
    expireUnix = expire.toTime.toUnix.uint64
    v = Voucher(relayPeerId: r.switch.peerInfo.peerId,
                  reservingPeerId: pid,
                  expiration: expireUnix)
    sv = ? SignedVoucher.init(r.switch.peerInfo.privateKey, v)
    ma = ? MultiAddress.init("/p2p/" & $r.switch.peerInfo.peerId).orErr(CryptoError.KeyError)
    rsrv = Reservation(expire: expireUnix,
                       addrs: r.switch.peerInfo.addrs.mapIt(
                         ? it.concat(ma).orErr(CryptoError.KeyError)),
                       svoucher: some(? sv.encode))
    msg = HopMessage(msgType: HopMessageType.Status,
                     reservation: some(rsrv),
                     limit: r.limit,
                     status: some(Ok))
  return ok(msg)

proc isRelayed(conn: Connection): bool =
  var wrappedConn = conn
  while not isNil(wrappedConn):
    if wrappedConn of RelayConnection:
      return true
    wrappedConn = wrappedConn.getWrapped()
  return false

proc handleReserve(r: Relay, conn: Connection) {.async, gcsafe.} =
  if conn.isRelayed():
    trace "reservation attempt over relay connection", pid = conn.peerId
    await sendHopStatus(conn, PermissionDenied)
    return

  if r.peerCount[conn.peerId] + r.rsvp.len() >= r.maxCircuit:
    trace "Too many reservations", pid = conn.peerId
    await sendHopStatus(conn, ReservationRefused)
    return
  let
    pid = conn.peerId
    expire = now().utc + r.reservationTTL
    msg = r.createReserveResponse(pid, expire)

  trace "reserving relay slot for", pid
  if msg.isErr():
    trace "error signing the voucher", error = error(msg), pid
    return
  r.rsvp[pid] = expire
  await conn.writeLp(encode(msg.get()).buffer)

proc handleConnect(r: Relay,
                   connSrc: Connection,
                   msg: HopMessage) {.async, gcsafe.} =
  if connSrc.isRelayed():
    trace "connection attempt over relay connection"
    await sendHopStatus(connSrc, PermissionDenied)
    return
  if msg.peer.isNone():
    await sendHopStatus(connSrc, MalformedMessage)
    return

  let
    src = connSrc.peerId
    dst = msg.peer.get().peerId
  if dst notin r.rsvp:
    trace "refusing connection, no reservation", src, dst
    await sendHopStatus(connSrc, NoReservation)
    return

  r.peerCount.inc(src)
  r.peerCount.inc(dst)
  defer:
    r.peerCount.inc(src, -1)
    r.peerCount.inc(dst, -1)

  if r.peerCount[src] > r.maxCircuitPerPeer or
     r.peerCount[dst] > r.maxCircuitPerPeer:
    trace "too many connections", src = r.peerCount[src],
                                  dst = r.peerCount[dst],
                                  max = r.maxCircuitPerPeer
    await sendHopStatus(connSrc, ResourceLimitExceeded)
    return

  let connDst = try:
    await r.switch.dial(dst, RelayV2StopCodec)
  except CancelledError as exc:
    raise exc
  except CatchableError as exc:
    trace "error opening relay stream", dst, exc=exc.msg
    await sendHopStatus(connSrc, ConnectionFailed)
    return
  defer:
    await connDst.close()

  proc sendStopMsg() {.async.} =
    let stopMsg = StopMessage(msgType: StopMessageType.Connect,
                            peer: some(Peer(peerId: src, addrs: @[])),
                            limit: r.limit)
    await connDst.writeLp(encode(stopMsg).buffer)
    let msg = StopMessage.decode(await connDst.readLp(r.msgSize)).get()
    if msg.msgType != StopMessageType.Status:
      raise newException(SendStopError, "Unexpected stop response, not a status message")
    if msg.status.get(UnexpectedMessage) != Ok:
      raise newException(SendStopError, "Relay stop failure")
    await connSrc.writeLp(encode(HopMessage(msgType: HopMessageType.Status,
                                          status: some(Ok))).buffer)
  try:
    await sendStopMsg()
  except CancelledError as exc:
    raise exc
  except CatchableError as exc:
    trace "error sending stop message", msg = exc.msg
    await sendHopStatus(connSrc, ConnectionFailed)
    return

  trace "relaying connection", src, dst
  let
    rconnSrc = RelayConnection.new(connSrc, r.limit.duration, r.limit.data)
    rconnDst = RelayConnection.new(connDst, r.limit.duration, r.limit.data)
  defer:
    await rconnSrc.close()
    await rconnDst.close()
  await bridge(rconnSrc, rconnDst)

proc handleHopStreamV2*(r: Relay, conn: Connection) {.async, gcsafe.} =
  let msgOpt = HopMessage.decode(await conn.readLp(r.msgSize))
  if msgOpt.isNone():
    await sendHopStatus(conn, MalformedMessage)
    return
  trace "relayv2 handle stream", msg = msgOpt.get()
  let msg = msgOpt.get()
  case msg.msgType:
  of HopMessageType.Reserve: await r.handleReserve(conn)
  of HopMessageType.Connect: await r.handleConnect(conn, msg)
  else:
    trace "Unexpected relayv2 handshake", msgType=msg.msgType
    await sendHopStatus(conn, MalformedMessage)

# Relay V1

proc handleHop*(r: Relay, connSrc: Connection, msg: RelayMessage) {.async, gcsafe.} =
  r.streamCount.inc()
  defer: r.streamCount.dec()
  if r.streamCount + r.rsvp.len() >= r.maxCircuit:
    trace "refusing connection; too many active circuit", streamCount = r.streamCount, rsvp = r.rsvp.len()
    await sendStatus(connSrc, StatusV1.HopCantSpeakRelay)
    return

  proc checkMsg(): Result[RelayMessage, StatusV1] =
    if msg.srcPeer.isNone:
      return err(StatusV1.HopSrcMultiaddrInvalid)
    let src = msg.srcPeer.get()
    if src.peerId != connSrc.peerId:
      return err(StatusV1.HopSrcMultiaddrInvalid)
    if msg.dstPeer.isNone:
      return err(StatusV1.HopDstMultiaddrInvalid)
    let dst = msg.dstPeer.get()
    if dst.peerId == r.switch.peerInfo.peerId:
      return err(StatusV1.HopCantRelayToSelf)
    if not r.switch.isConnected(dst.peerId):
      trace "relay not connected to dst", dst
      return err(StatusV1.HopNoConnToDst)
    ok(msg)
  let check = checkMsg()
  if check.isErr:
    await sendStatus(connSrc, check.error())
    return

  let
    src = msg.srcPeer.get()
    dst = msg.dstPeer.get()
  if r.peerCount[src.peerId] >= r.maxCircuitPerPeer or
     r.peerCount[dst.peerId] >= r.maxCircuitPerPeer:
    trace "refusing connection; too many connection from src or to dst", src, dst
    await sendStatus(connSrc, StatusV1.HopCantSpeakRelay)
    return
  r.peerCount.inc(src.peerId)
  r.peerCount.inc(dst.peerId)
  defer:
    r.peerCount.inc(src.peerId, -1)
    r.peerCount.inc(dst.peerId, -1)

  let connDst = try:
    await r.switch.dial(dst.peerId, RelayV1Codec)
  except CancelledError as exc:
    raise exc
  except CatchableError as exc:
    trace "error opening relay stream", dst, exc=exc.msg
    await sendStatus(connSrc, StatusV1.HopCantDialDst)
    return
  defer:
    await connDst.close()

  let msgToSend = RelayMessage(
    msgType: some(RelayType.Stop),
    srcPeer: some(src),
    dstPeer: some(dst))

  let msgRcvFromDstOpt = try:
    await connDst.writeLp(encode(msgToSend).buffer)
    RelayMessage.decode(await connDst.readLp(r.msgSize))
  except CancelledError as exc:
    raise exc
  except CatchableError as exc:
    trace "error writing stop handshake or reading stop response", exc=exc.msg
    await sendStatus(connSrc, StatusV1.HopCantOpenDstStream)
    return

  if msgRcvFromDstOpt.isNone:
    trace "error reading stop response", msg = msgRcvFromDstOpt
    await sendStatus(connSrc, StatusV1.HopCantOpenDstStream)
    return

  let msgRcvFromDst = msgRcvFromDstOpt.get()
  if msgRcvFromDst.msgType.get(RelayType.Stop) != RelayType.Status or
     msgRcvFromDst.status.get(StatusV1.StopRelayRefused) != StatusV1.Success:
    trace "unexcepted relay stop response", msgRcvFromDst
    await sendStatus(connSrc, StatusV1.HopCantOpenDstStream)
    return

  await sendStatus(connSrc, StatusV1.Success)
  trace "relaying connection", src, dst
  await bridge(connSrc, connDst)

proc handleStreamV1(r: Relay, conn: Connection) {.async, gcsafe.} =
  let msgOpt = RelayMessage.decode(await conn.readLp(r.msgSize))
  if msgOpt.isNone:
    await sendStatus(conn, StatusV1.MalformedMessage)
    return
  trace "relay handle stream", msg = msgOpt.get()
  let msg = msgOpt.get()
  case msg.msgType.get:
    of RelayType.Hop: await r.handleHop(conn, msg)
    of RelayType.Stop: await sendStatus(conn, StatusV1.StopRelayRefused)
    of RelayType.CanHop: await sendStatus(conn, StatusV1.Success)
    else:
      trace "Unexpected relay handshake", msgType=msg.msgType
      await sendStatus(conn, StatusV1.MalformedMessage)

proc setup*(r: Relay, switch: Switch) =
  r.switch = switch
  r.switch.addPeerEventHandler(
    proc (peerId: PeerId, event: PeerEvent) {.async.} =
      r.rsvp.del(peerId),
    Left)

proc new*(T: typedesc[Relay],
     reservationTTL: times.Duration = DefaultReservationTTL,
     limitDuration: uint32 = DefaultLimitDuration,
     limitData: uint64 = DefaultLimitData,
     heartbeatSleepTime: uint32 = DefaultHeartbeatSleepTime,
     maxCircuit: int = MaxCircuit,
     maxCircuitPerPeer: int = MaxCircuitPerPeer,
     msgSize: int = RelayMsgSize,
     circuitRelayV1: bool = false): T =

  let r = T(reservationTTL: reservationTTL,
            limit: Limit(duration: limitDuration, data: limitData),
            heartbeatSleepTime: heartbeatSleepTime,
            maxCircuit: maxCircuit,
            maxCircuitPerPeer: maxCircuitPerPeer,
            msgSize: msgSize,
            isCircuitRelayV1: circuitRelayV1)

  proc handleStream(conn: Connection, proto: string) {.async, gcsafe.} =
    try:
      case proto:
      of RelayV2HopCodec: await r.handleHopStreamV2(conn)
      of RelayV1Codec: await r.handleStreamV1(conn)
    except CancelledError as exc:
      raise exc
    except CatchableError as exc:
      debug "exception in relayv2 handler", exc = exc.msg, conn
    finally:
      trace "exiting relayv2 handler", conn
      await conn.close()

  r.codecs = if r.isCircuitRelayV1: @[RelayV1Codec]
             else: @[RelayV2HopCodec, RelayV1Codec]
  r.handler = handleStream
  r

proc deletesReservation(r: Relay) {.async.} =
  heartbeat "Reservation timeout", r.heartbeatSleepTime.seconds():
    let n = now().utc
    for k in toSeq(r.rsvp.keys):
      if n > r.rsvp[k]:
        r.rsvp.del(k)

method start*(r: Relay) {.async.} =
  if not r.reservationLoop.isNil:
    warn "Starting relay twice"
    return
  r.reservationLoop = r.deletesReservation()
  r.started = true

method stop*(r: Relay) {.async.} =
  if r.reservationLoop.isNil:
    warn "Stopping relay without starting it"
    return
  r.started = false
  r.reservationLoop.cancel()
  r.reservationLoop = nil