{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MultiWayIf #-}
module Server where

import Prelude hiding (Word)

import Control.Concurrent.STM
import Control.Monad (void)
import Control.Monad.Loops (iterateUntilM)
import Data.List (delete)
import qualified Data.Map.Strict as Map
import Data.Map.Strict (Map)
import System.Random

import Types


data ServerIn = ServerIn ServerIn' (TMVar [ServerOut])

data ServerIn'
    = IAnon Cmd
    | IAs User Cmd
  deriving (Show)

data ServerOut
    = OResponse Response
    | OLogin User
    | OLogout
    | ODisconnect
  deriving (Show)

data ClientAction
    = CAResponse Response
    | CAPush Push
    | CADisconnect
  deriving (Show)

data ClientState
    = CSDisconnected
    | CSAnon
    | CSUser User
    | CSVersionWait
  deriving (Show)

clientGate :: TQueue ServerIn -> TQueue (Maybe Cmd) -> TQueue ClientAction -> IO ()
clientGate server clientIn clientOut =
    void $ iterateUntilM (\case CSDisconnected -> True ; _ -> False) body CSVersionWait
  where
    body state = do
        atomically (readTQueue clientIn) >>= \case
            Nothing -> return CSDisconnected
            Just (CVersion (Word "3")) -> do
                atomically (writeTQueue clientOut (CAResponse ROk))
                case state of
                    CSVersionWait -> return CSAnon
                    _ -> return state
            Just (CVersion _) -> do
                atomically (writeTQueue clientOut (CAResponse (RError "Version not supported")))
                return CSVersionWait
            Just cmd -> do
                let msg = case state of CSAnon -> IAnon cmd
                                        CSUser u -> IAs u cmd
                                        _ -> error "impossible"
                resVar <- newEmptyTMVarIO
                atomically (writeTQueue server (ServerIn msg resVar))
                outs <- atomically (readTMVar resVar)
                loopM outs state $ curry $ \case
                    (CSDisconnected, _) -> return CSDisconnected
                    (state', OResponse res) -> do
                        atomically (writeTQueue clientOut (CAResponse res))
                        return state'
                    (_, OLogin u) -> return (CSUser u)
                    (_, OLogout) -> return CSAnon
                    (_, ODisconnect) -> return CSDisconnected

data ServerState
    = ServerState { ssRooms :: Map Room RoomState
                  , ssUsers :: Map User UserData
                  , ssRNG :: StdGen }
  deriving (Show)

data RoomState
    = RoomState { rsHistory :: Map Id HistoryItem
                , rsMembers :: [User] }
  deriving (Show)

data UserData
    = UserData { udPassword :: Line }
  deriving (Show)

data HistoryItem
    = HIMsg { hiId :: Id
            , hiTimestamp :: Int
            , hiUser :: User
            , hiReplyId :: Maybe Id
            , hiLine :: Line }
  deriving (Show)

initialServerState :: ServerState
initialServerState =
    ServerState { ssRooms = mempty
                , ssUsers = mempty
                , ssRNG = mkStdGen 1234 }

emptyRoomState :: RoomState
emptyRoomState =
    RoomState { rsHistory = mempty
              , rsMembers = [] }

serverHandleEvent :: ServerState -> ServerIn' -> (ServerState, [ServerOut])
serverHandleEvent state = \case
    IAnon (CRegister u p)
      | u `Map.member` ssUsers state -> (state, [OResponse (RError "User already exists")])
      | otherwise -> (state { ssUsers = Map.insert u (UserData p) (ssUsers state) }
                     ,[OResponse ROk])

    IAnon (CLogin u p)
      | Just ud <- Map.lookup u (ssUsers state)
      , p == udPassword ud
      -> (state, [OResponse ROk, OLogin u])
      | otherwise -> (state, [OResponse (RError "Invalid password")])

    IAnon _ -> (state, [OResponse (RError "Not logged in")])

    IAs user cmd -> case cmd of
        CChangePassword p ->
            (state { ssUsers = Map.adjust (\ud -> ud { udPassword = p }) user (ssUsers state) }
            ,[OResponse ROk])

        CLogout -> (state, [OResponse ROk, OLogout])

        CListRooms -> (state, [OResponse (RList (map fromRoom (Map.keys (ssRooms state))))])

        CListMembers r
          | Just (RoomState { rsMembers = mbs }) <- Map.lookup r (ssRooms state)
          , user `elem` mbs
          -> (state, [OResponse (RList (map fromUser mbs))])
          | otherwise
          -> (state, [OResponse (RError "Room not found")])

        CCreateRoom ->
            let (rng', roomid) = genRoomId (ssRNG state)
            in (state { ssRooms = Map.insert roomid emptyRoomState (ssRooms state)
                      , ssRNG = rng' }
               ,[OResponse (RName (fromRoom roomid))])

        CLeaveRoom r
          | Just rs@(RoomState { rsMembers = mbs }) <- Map.lookup r (ssRooms state)
          , user `elem` mbs
          -> (state { ssRooms = Map.insert r (rs { rsMembers = delete user mbs }) (ssRooms state) }
             ,[OResponse ROk])
          | otherwise
          -> (state, [OResponse (RError "Not in that room")])

        CInvite r u
          | Just (RoomState { rsMembers = mbs }) <- Map.lookup r (ssRooms state)
          , user `elem` mbs
          -> if | user `Map.notMember` ssUsers state -> (state, [OResponse (RError "User not found")])
                | user `elem` mbs -> (state, [OResponse (RError "User already in room")])
                | otherwise ->
                    (state { ssRooms = Map.adjust (\rs -> rs { rsMembers = u : rsMembers rs })
                                                  r (ssRooms state) }
                    ,[OResponse ROk, push_to_u_something, broadcast_something])
         | otherwise
         -> (state, [OResponse (RError "Not in that room")])

loopM :: Monad m => [a] -> s -> (s -> a -> m s) -> m s
loopM [] s _ = return s
loopM (x:xs) s f = f s x >>= \s' -> loopM xs s' f

genRoomId :: RandomGen g => g -> (g, Room)
genRoomId gen =
    let (is, gen') = uniformRN 8 (0, 2 * 26) gen
    in (gen', Room (Word (map ((['a'..'z'] ++ ['A'..'Z']) !!) is)))
  where
    uniformRN :: (RandomGen g, UniformRange a) => Int -> (a, a) -> g -> ([a], g)
    uniformRN 0 r g = let (x, g') = uniformR r g
                      in ([x], g')
    uniformRN n r g = let (x, g') = uniformR r g
                          (xs, g'') = uniformRN (n-1) r g'
                      in (x:xs, g'')