-- | This module implements Scuttlebutt's Remote Procedure Call for
-- Rooms.
--
-- For more information kindly refer [WHERE]

-- TODO: Documentation for SSB-Room

module Ssb.Peer.RPC.Room where


import           Protolude               hiding ( Identity )
import qualified Data.Aeson                    as Aeson
import           Control.Concurrent.STM
import           Data.Default
import qualified Data.Map.Strict               as Map
import           Data.Time.Clock                ( UTCTime
                                                , getCurrentTime
                                                )
import qualified Data.Text                     as Text

import  Ssb.Aux
import qualified Ssb.Identity                  as Ssb
import qualified Ssb.Pub                       as Ssb
import           Ssb.Network
import qualified Ssb.Feed                      as Feed
import qualified Ssb.Peer.RPC                  as RPC

seed :: Text
seed = "SSB+Room+PSK3TLYC2T86EHQCUHBUHASCASE18JBV24="

data Invite = Invite
    { host :: Host
    , port :: Port
    , key  :: Ssb.PublicKey
    } deriving (Eq, Show)

formatInvite :: Invite -> Text
formatInvite arg =
  "net:"
    <> host arg
    <> ":"
    <> port arg
    <> "~shs"
    <> ":"
    <> formatPublicKey' arg
    <> ":"
    <> seed
 where
  formatPublicKey' arg =
    Text.dropEnd 8 $ Text.drop 1 $ Ssb.formatPublicKey $ key arg

-- TODO: Seriously, figure out how to use duplicate field names
data Room = Room {
      endpoints     :: TMVar (Map Ssb.PublicKey (RPC.ConnState, [Tunnel]))
    , notifyChange  :: TChan Bool
    , roomName      :: Text
    , roomDesc      :: Text
    , tunnels       :: TMVar (Map Tunnel [ThreadId])
    }

newRoom :: Text -> Text -> IO Room
newRoom name desc = do
  endpoints <- newTMVarIO Map.empty
  notifier  <- newBroadcastTChanIO
  tunnels   <- newTMVarIO Map.empty
  return $ Room endpoints notifier name desc tunnels

getEndpoints :: Room -> IO [Ssb.PublicKey]
getEndpoints h = do
  let mVar = endpoints h
  Map.keys <$> atomically (readTMVar mVar)

lookUpPeer :: Room -> Ssb.PublicKey -> IO (Maybe RPC.ConnState)
lookUpPeer h peer = do
  endpoints' <- atomically $ readTMVar (endpoints h)
  return $ fst <$> Map.lookup peer endpoints'

errConnLimitReached = "peer limit reached"

registerPeer :: Room -> RPC.Stream -> IO (Either Text ())
registerPeer h stream = do
  let mVar = endpoints h
  atomically $ do
    endpoints' <- takeTMVar mVar
    if Map.size endpoints' == (maxBound :: Int)
      then return $ Left errConnLimitReached
      else do
        putTMVar mVar
          $ Map.insert (RPC.peer stream) (RPC.conn stream, []) endpoints'
        writeTChan (notifyChange h) True
        return $ Right ()

unregisterPeer :: Room -> Ssb.PublicKey -> IO ()
unregisterPeer h peer = do
  let mVar = endpoints h
  atomically $ do
    endpoints' <- takeTMVar mVar
    putTMVar mVar $ Map.delete peer endpoints'
    writeTChan (notifyChange h) True

data IsRoomResponse = IsRoomResponse {
      name          :: Text
    , description   :: Text
    } deriving (Generic, Show)

instance Aeson.FromJSON IsRoomResponse

instance Aeson.ToJSON IsRoomResponse

newIsRoomResponse :: Room -> IsRoomResponse
newIsRoomResponse l = IsRoomResponse (roomName l) (roomDesc l)

announceRequest :: RPC.Request [Text]
announceRequest =
  RPC.Request { name = ["tunnel", "announce"], typ = RPC.Async, args = [] }

announce :: RPC.ConnState -> IO (Either Text ())
announce conn = RPC.requestAsync conn announceRequest

data ConnectRequest = ConnectRequest {
      target   :: Ssb.PublicKey
    , portal   :: Ssb.PublicKey
    } deriving (Generic, Show)

instance Aeson.FromJSON ConnectRequest

instance Aeson.ToJSON ConnectRequest

leaveRequest :: RPC.Request [Text]
leaveRequest =
  RPC.Request { name = ["tunnel", "leave"], typ = RPC.Async, args = [] }

leave :: RPC.ConnState -> IO (Either Text ())
leave conn = RPC.requestAsync conn leaveRequest

pingRequest :: RPC.Request [Text]
pingRequest =
  RPC.Request { name = ["tunnel", "ping"], typ = RPC.Async, args = [] }

ping :: RPC.ConnState -> IO (Either Text UTCTime)
ping conn = RPC.requestAsync conn pingRequest

-- | fork creates a new thread, incrementing the counter in the given mVar.
fork mVar action = do
  fork' <- newEmptyTMVarIO
  atomically $ do
    forks <- takeTMVar mVar
    putTMVar mVar $ fork' : forks
  forkFinally
    action
    (\_ -> do
      atomically $ putTMVar fork' ()
    )

-- | wait returns when all forks have completed.
waitForkGroup mVar threads = do
  cs <- atomically $ takeTMVar mVar
  case cs of
    []     -> return ()
    m : ms -> do
      atomically $ putTMVar mVar ms
      atomically $ takeTMVar m
      forM_ threads killThread
      waitForkGroup mVar []

forwardMessages :: RPC.Stream -> RPC.Stream -> IO (Either Text ())
forwardMessages s1 s2 = do
  mMsg <- RPC.readStream s1
  case mMsg of
    Nothing  -> return $ Right ()
    Just msg -> do
      res <- RPC.writeStream s2 def msg
      case res of
        Left  err -> return $ Left err
        Right _   -> forwardMessages s1 s2

type Tunnel = (Ssb.PublicKey, Ssb.PublicKey)

newTunnel arg1 arg2 =
  -- the tunnel's entries need to be ordered to make pairs unique
  if arg1 < arg2 then (arg1, arg2) else (arg2, arg1)

createTunnel :: Room -> (RPC.Stream, RPC.Stream) -> IO (Either Text ())
createTunnel room (stream1, stream2) = do
  let peer1  = RPC.connPeer $ RPC.conn stream1
  let peer2  = RPC.connPeer $ RPC.conn stream2
  let tunnel = newTunnel peer1 peer2

  exists <- atomically $ do
    tunnels' <- readTMVar (tunnels room)
    return $ Map.member tunnel tunnels'
  if exists
    then return $ Left "only one tunnel allowed"
    else do
      waiter  <- newTMVarIO []
      thread1 <- fork waiter $ forwardMessages stream1 stream2
      thread2 <- fork waiter $ forwardMessages stream2 stream1
      let threads = [thread1, thread2]

      atomically $ do
        endpoints' <- takeTMVar (endpoints room)
        let endpoints'' = Map.adjust (addTunnel tunnel) (fst tunnel) endpoints'
        let endpoints''' =
              Map.adjust (addTunnel tunnel) (snd tunnel) endpoints''
        putTMVar (endpoints room) endpoints'''

        tunnels' <- takeTMVar (tunnels room)
        let tunnels'' = Map.insert tunnel threads tunnels'
        putTMVar (tunnels room) tunnels''

      waitForkGroup waiter threads

      atomically $ do
        endpoints' <- takeTMVar (endpoints room)
        let endpoints'' =
              Map.adjust (removeTunnel tunnel) (fst tunnel) endpoints'
        let endpoints''' =
              Map.adjust (removeTunnel tunnel) (snd tunnel) endpoints''
        putTMVar (endpoints room) endpoints'''

        tunnels' <- takeTMVar (tunnels room)
        putTMVar (tunnels room) $ Map.delete tunnel tunnels'

      return . return $ ()
 where
  addTunnel arg (conn, tunnels) = (conn, tunnels ++ [arg])
  removeTunnel arg (conn, tunnels) = (conn, filter (arg /=) tunnels)

connect :: Room -> RPC.Stream -> ConnectRequest -> IO (Either Text ())
connect room stream req = do
  let tunnel = newTunnel (RPC.connPeer $ RPC.conn $ stream) (target req)
  tunnels' <- atomically $ readTMVar (tunnels room)
  mPeer    <- lookUpPeer room (target req)
  let peerConn = do
        bool (return ()) errSelfNotAllowed   (fst tunnel == snd tunnel)
        bool (return ()) errOnlyUniqueTunnel (Map.member tunnel tunnels')
        maybeToRight errPeerNotAvailable mPeer
  case peerConn of
    Left err -> do
      putStrLn $ "room error:  " <> err
      return $ Left err
    Right conn -> RPC.request conn (rpcRequest req)
      $ \peerStream -> createTunnel room (stream, peerStream)
 where
  errOnlyUniqueTunnel = Left $ "only unique tunnels are allowed"
  errPeerNotAvailable = "peer is not connected" :: Text
  errSelfNotAllowed   = Left $ "connecting to self not allowed"
  rpcRequest arg =
    RPC.Request { name = ["tunnel", "connect"], typ = RPC.Duplex, args = [arg] }

leave' :: Room -> Ssb.PublicKey -> IO (Either Text ())
leave' room peer = do
  endpoints' <- atomically $ readTMVar (endpoints room)
  tunnels'   <- atomically $ readTMVar (tunnels room)

  let etunnels = fromMaybe mempty $ snd <$> Map.lookup peer endpoints'
  forM_ etunnels $ \tunnel -> do
    let threads = fromMaybe mempty $ Map.lookup tunnel tunnels'
    forM_ threads killThread
  unregisterPeer room peer
  return . return $ ()

instance RPC.Handler Room where
  endpoints _ =
    [ RPC.Endpoint ["tunnel", "announce"] RPC.Async
    , RPC.Endpoint ["tunnel", "connect"] RPC.Duplex
    , RPC.Endpoint ["tunnel", "endpoints"] RPC.Async
    , RPC.Endpoint ["tunnel", "leave"] RPC.Async
    , RPC.Endpoint ["tunnel", "isRoom"] RPC.Async
    , RPC.Endpoint ["tunnel", "ping"] RPC.Async
    ]

    -- The announce and leave endpoints are defined by the server's JS, but
    -- never called by the client.  The official (NodeJS) project uses
    -- disconnect notifications from the SSB-server.
    --
  serve h (RPC.Endpoint ["tunnel", "announce"] _) args stream =
    registerPeer h stream

  -- should decode request
  serve h (RPC.Endpoint ["tunnel", "connect"] RPC.Duplex) args stream = do
    let args' =
          decodeJSON (toS $ Aeson.encode args) :: Either
              Text
              [ConnectRequest]
    case args' of
      Left  err       -> return $ Left err
      Right [connReq] -> connect h stream connReq
      otherwise       -> return $ Left "bad target argument"

  serve h (RPC.Endpoint ["tunnel", "endpoints"] _) _ stream = do
    err <- registerPeer h stream
    case err of
      Left  msg -> return $ Left msg
      Right _   -> do
        change <- atomically $ dupTChan $ notifyChange h
        while $ do
          endpoints' <- getEndpoints h
          let resp = filter (/= RPC.peer stream) endpoints'
          res <- RPC.writeStreamJSON stream resp
          if isLeft res then return False else atomically $ readTChan change
        return $ Right ()
   where
    while f = do
      continue <- f
      if continue then (while f) else return False

  serve room (RPC.Endpoint ["tunnel", "leave"] _) _ stream =
    leave' room (RPC.peer stream)

  serve room (RPC.Endpoint ["tunnel", "isRoom"] _) _ stream =
    RPC.writeStreamJSON stream (newIsRoomResponse room)

  serve room (RPC.Endpoint ["tunnel", "ping"] _) _ stream = do
    resp <- getCurrentTime
    RPC.writeStreamJSON stream resp

  serve room endpoint@otherwise arg stream = (RPC.notFoundHandlerFunc endpoint) arg stream

  notifyConnect _ _ = return . return $ ()

  notifyDisconnect room peer = do
    _ <- leave' room peer
    return . return $ ()