{-# LANGUAGE CPP                 #-}
{-# LANGUAGE OverloadedStrings   #-}
{-# LANGUAGE RankNTypes          #-}
{-# LANGUAGE ScopedTypeVariables #-}

-- | Most of the hairy code. This isn't all internal, due to messy
-- dependencies, but I've tried to make this as \"internal\" as
-- reasonably possible.
module Network.IRC.Client.Internal where

import Control.Applicative        ((<$>))
import Control.Concurrent         (forkIO)
import Control.Concurrent.STM     (atomically, readTVar, retry, writeTVar)
import Control.Exception          (SomeException, catch, throwIO)
import Control.Monad              (unless, when)
import Control.Monad.IO.Class     (MonadIO, liftIO)
import Control.Monad.Trans.Reader (runReaderT)
import Data.ByteString            (ByteString)
import Data.Conduit               (Producer, Conduit, Consumer, (=$=), ($=), (=$), await, awaitForever, toProducer, yield)
import Data.Conduit.TMChan        (closeTBMChan, isEmptyTBMChan, newTBMChanIO, sourceTBMChan, writeTBMChan)
import Data.Text.Encoding         (decodeUtf8, encodeUtf8)
import Data.Time.Clock            (NominalDiffTime, addUTCTime, getCurrentTime)
import Data.Time.Format           (formatTime)
import Network.IRC.Conduit        (IrcEvent, IrcMessage, floodProtector, rawMessage, toByteString)
import Network.IRC.Client.Types

#if MIN_VERSION_time(1,5,0)
import Data.Time.Format (defaultTimeLocale)
#else
import System.Locale    (defaultTimeLocale)
#endif

-- * Connecting to an IRC network

-- | Connect to a server using the supplied connection function.
connectInternal :: MonadIO m
  => (Int -> ByteString -> IO () -> Consumer (Either ByteString IrcEvent) IO () -> Producer IO IrcMessage -> IO ())
  -- ^ Function to start the network conduits.
  -> StatefulIRC s ()
  -- ^ Connect handler
  -> StatefulIRC s ()
  -- ^ Disconnect handler
  -> (Origin -> ByteString -> IO ())
  -- ^ Logging function
  -> ByteString
  -- ^ Server hostname
  -> Int
  -- ^ Server post
  -> NominalDiffTime
  -- ^ Flood timeout
  -> m (ConnectionConfig s)
connectInternal f onconnect ondisconnect logf host port flood = liftIO $ do
  queueS <- newTBMChanIO 16

  return ConnectionConfig
    { _func         = f
    , _sendqueue    = queueS
    , _server       = host
    , _port         = port
    , _flood        = flood
    , _onconnect    = onconnect
    , _ondisconnect = ondisconnect
    , _logfunc      = logf
    }

-- * Event loop

-- | The event loop.
runner :: StatefulIRC s ()
runner = do
  state <- ircState

  -- Set the real- and user-name
  theUser  <- _username <$> instanceConfig
  theReal  <- _realname <$> instanceConfig
  password <- _password <$> instanceConfig

  -- Initialise the IRC session
  let initialise = flip runReaderT state $ do
        liftIO . atomically $ writeTVar (_connState state) Connected
        mapM_ (\p -> sendBS $ rawMessage "PASS" [encodeUtf8 p]) password
        sendBS $ rawMessage "USER" [encodeUtf8 theUser, "-", "-", encodeUtf8 theReal]
        _onconnect =<< connectionConfig

  -- Run the event loop, and call the disconnect handler if the remote
  -- end closes the socket.
  cconf <- connectionConfig
  let flood  = _flood     cconf
  let func   = _func      cconf
  let logf   = _logfunc   cconf
  let port   = _port      cconf
  let queue  = _sendqueue cconf
  let server = _server    cconf

  antiflood <- liftIO $ floodProtector flood

  dchandler <- _ondisconnect <$> connectionConfig

  let source = toProducer $ sourceTBMChan queue $= antiflood $= logConduit (logf FromClient . toByteString)
  let sink   = forgetful =$= logConduit (logf FromServer . _raw) =$ eventSink state

  (exc :: Maybe SomeException) <- liftIO $ catch
    (func port server initialise sink source >> pure Nothing)
    (pure . Just)

  disconnect
  dchandler

  -- If the connection terminated due to an exception, rethrow it.
  liftIO $ maybe (pure ()) throwIO exc

-- | Forget failed decodings.
forgetful :: Monad m => Conduit (Either a b) m b
forgetful = awaitForever go where
  go (Left  _) = return ()
  go (Right b) = yield b

-- | Block on receiving a message and invoke all matching handlers
-- concurrently.
eventSink :: MonadIO m => IRCState s -> Consumer IrcEvent m ()
eventSink ircstate = await >>= maybe (return ()) (\event -> do
  let event'  = decodeUtf8 <$> event
  ignored <- isIgnored ircstate event'
  unless ignored $ do
    handlers <- getHandlersFor event' . _eventHandlers <$> getInstanceConfig' ircstate
    liftIO $ mapM_ (\h -> forkIO $ runReaderT (h event') ircstate) handlers

  -- If disconnected, do not loop.
  disconnected <- (==Disconnected) <$> getConnState ircstate
  unless disconnected (eventSink ircstate))

-- | Check if an event is ignored or not.
isIgnored :: MonadIO m => IRCState s -> UnicodeEvent -> m Bool
isIgnored ircstate ev = do
  iconf <- liftIO . atomically . readTVar . _instanceConfig $ ircstate
  let ignoreList = _ignore iconf

  return $
    case _source ev of
      User      n ->  (n, Nothing) `elem` ignoreList
      Channel c n -> ((n, Nothing) `elem` ignoreList) || ((n, Just c) `elem` ignoreList)
      Server  _   -> False

-- |Get the event handlers for an event.
getHandlersFor :: Event a -> [EventHandler s] -> [UnicodeEvent -> StatefulIRC s ()]
getHandlersFor e ehs = [_eventFunc eh | eh <- ehs, _matchType eh `elem` [EEverything, eventType e]]

-- |A conduit which logs everything which goes through it.
logConduit :: MonadIO m => (a -> IO ()) -> Conduit a m a
logConduit logf = awaitForever $ \x -> do
  -- Call the logging function
  liftIO $ logf x

  -- And pass the message on
  yield x

-- | Print messages to stdout, with the current time.
stdoutLogger :: Origin -> ByteString -> IO ()
stdoutLogger origin x = do
  now <- getCurrentTime

  putStrLn $ unwords
    [ formatTime defaultTimeLocale "%c" now
    , if origin == FromServer then "<---" else "--->"
    , init . tail $ show x
    ]

-- | Append messages to a file, with the current time.
fileLogger :: FilePath -> Origin -> ByteString -> IO ()
fileLogger fp origin x = do
  now <- getCurrentTime

  appendFile fp $ unwords
    [ formatTime defaultTimeLocale "%c" now
    , if origin == FromServer then "--->" else "<---"
    , init . tail $ show x
    , "\n"
    ]

-- | Do no logging.
noopLogger :: a -> b -> IO ()
noopLogger _ _ = return ()

-- * Messaging

-- | Send a message as UTF-8, using TLS if enabled. This blocks if
-- messages are sent too rapidly.
send :: UnicodeMessage -> StatefulIRC s ()
send = sendBS . fmap encodeUtf8

-- | Send a message, using TLS if enabled. This blocks if messages are
-- sent too rapidly.
sendBS :: IrcMessage -> StatefulIRC s ()
sendBS msg = do
  queue <- _sendqueue <$> connectionConfig
  liftIO . atomically $ writeTBMChan queue msg

-- * Disconnecting

-- | Disconnect from the server, properly tearing down the TLS session
-- (if there is one).
disconnect :: StatefulIRC s ()
disconnect = do
  s <- ircState

  connState <- liftIO . atomically . readTVar $ _connState s
  case connState of
    Connected -> do
      -- Set the state to @Disconnecting@
      liftIO . atomically $ writeTVar (_connState s) Disconnecting

      -- Wait for all messages to be sent, or a minute has passed.
      queueS <- _sendqueue <$> connectionConfig
      timeout 60 . atomically $ isEmptyTBMChan queueS

      -- Then close the connection
      disconnectNow

    -- If already disconnected, or disconnecting, do nothing.
    _ -> pure ()

-- | Disconnect immediately, without waiting for messages to be sent.
disconnectNow :: StatefulIRC s ()
disconnectNow = do
  queueS <- _sendqueue <$> connectionConfig
  liftIO . atomically $ closeTBMChan queueS

  s <- ircState
  liftIO . atomically $ writeTVar (_connState s) Disconnected

-- | Block until an action is successful or a timeout is reached.
timeout :: MonadIO m => NominalDiffTime -> IO Bool -> m ()
timeout dt check = liftIO $ do
  finish <- addUTCTime dt <$> getCurrentTime
  let wait = do
        now  <- getCurrentTime
        cond <- check
        when (now < finish && not cond) wait
  wait