{-# LANGUAGE CPP               #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeFamilies      #-}
module Main where

import System.Directory
import Control.Monad
import System.Posix.Signals
import System.Posix.Types
import System.Posix.Process
import Data.Maybe
import Data.Char

import System.INotify
#ifndef NOUTMP
import UTmp 
-- Breaks profiling build with error:
--     Dynamic linking required, but this is a non-standard build (eg. prof).
--         You need to build the program twice: once the normal way, and then
--             in the desired way using -osuf to set the object file suffix.
--
-- TODO: Figure out wtf ghc is trying to tell me.
--       In the mean time, use -DNOTMP to build for profiling.
-- 
#endif
import FGConsole
import XMPPServer
import Data.HList
import Network.Socket (sClose)
import Control.Exception
import LocalPeerCred
import System.Posix.User
import qualified Data.Set as Set
import           Data.Set as Set (Set,(\\))
import qualified Data.Map as Map
import           Data.Map as Map (Map)

import Control.Concurrent.STM
import Control.Concurrent (threadDelay)
import Control.Monad.Trans.Maybe
import Control.Monad.IO.Class

import ByteStringOperators
import qualified Data.ByteString.Lazy.Char8 as L
import           Data.ByteString.Lazy.Char8 as L (ByteString,putStrLn)
import qualified Prelude
import           Prelude hiding (putStrLn)


data UnixSession = UnixSession {
    unix_uid :: (IORef (Maybe UserID)),
    unix_resource :: (IORef (Maybe L.ByteString)),
    presence_state :: PresenceState
}

instance XMPPSession UnixSession where
    data XMPPClass UnixSession = UnixSessions PresenceState
    newSession (UnixSessions state) sock handle = do
        muid <- getLocalPeerCred sock
        L.putStrLn $ "SESSION: open " <++> bshow muid
        uid_ref <- newIORef muid
        res_ref <- newIORef Nothing
        return $ UnixSession uid_ref res_ref state
    setResource  s  resource    = do
        writeIORef (unix_resource s) (Just resource)
        L.putStrLn $ "SESSION: resource " <++> resource
    getJID       s             = do
        let host = "localhost" -- TODO
        muid <- readIORef (unix_uid s)
        user <- maybe (return "nobody") 
                   (\uid -> 
                        handle (\(SomeException _) -> 
                                return . L.append "uid." . L.pack . show $ uid)
                          $ do
                             user <- fmap userName $ getUserEntryForID uid
                             return (L.pack user)
                        )
                   muid
        rsc <- readIORef (unix_resource s)
        let suf = maybe "" ("/"<++>) rsc
            jid = user <++> "@" <++> L.pack host <++> suf
        L.putStrLn $ "SESSION: jid " <++> jid
        return jid
    closeSession _             = L.putStrLn "SESSION: close"
    subscribe session Nothing = do
        let tmvar = greedySubscriber (presence_state session)
        chan <- atomically $
            (do (cnt,chan) <- takeTMVar tmvar
                putTMVar tmvar (cnt+1,chan)
                chan' <- dupTChan chan
                return chan' )
          `orElse`
            (do chan <- newTChan
                putTMVar tmvar (1,chan)
                return chan )
        return chan
    subscribe session (Just jid) = do
        let tvar = subscriberMap (presence_state session)
        atomically $ do
            subs <- readTVar tvar
            let mbchan       = Map.lookup jid subs
            (chan,subs') <- 
                do case mbchan of
                    Nothing -> do
                      newchan <- newTChan
                      return (newchan, Map.insert jid (1,newchan) subs)
                    Just (cnt,chan) -> do
                      chan' <- dupTChan chan
                      return (chan', Map.insert jid (cnt+1,chan) subs)
            writeTVar tvar subs'
            return chan

matchResource tty jid = maybe Away (avail . (==tty)) $ resource jid
 where
    avail True  = Available
    avail False = Away

sendPresence chan jid status = 
    (liftIO  . atomically . writeTChan chan . Presence jid $ status) :: MaybeT IO ()

lookupT jid subscribers = MaybeT . return $ Map.lookup jid subscribers 

update_presence greedy subscribers state getStatus =
    forM_ (Set.toList state) $ \jid -> do
      let status = getStatus jid 
      runMaybeT $ do
        chan <- lookupT jid subscribers
        sendPresence chan jid status
      runMaybeT $ do
        chan <- MaybeT . return $ greedy
        sendPresence chan jid status
      putStrLn $ bshow jid <++> " " <++> bshow status

type RefCount = Int

data PresenceState = PresenceState 
    { currentTTY    :: TVar ByteString
    , activeUsers   :: TVar (Set JID)
    , subscriberMap :: TVar (Map JID (RefCount,TChan Presence))
    , greedySubscriber :: TMVar (RefCount,TChan Presence)
    }

newPresenceState = atomically $ do
    tty  <- newTVar ""
    us   <- newTVar (Set.empty)
    subs <- newTVar (Map.empty)
    greedy <- newEmptyTMVar
    return $ PresenceState tty us subs greedy

track_login state e = do
#ifndef NOUTMP
    us <- UTmp.users
#else
    let us = []
#endif
    let toJabberId host (user,tty,_) = 
            if L.take 3 tty == "tty"
              then Just (jid user host tty)
              else Nothing
        new_users = Set.fromList $ mapMaybe (toJabberId "localhost") us
    (tty,known_users,subs,greedy) <- atomically $ do
            tty <- readTVar                $ currentTTY state
            st  <- flip swapTVar new_users $ activeUsers state
            xs  <- readTVar                $ subscriberMap state
            greedy <- tryReadTMVar $ greedySubscriber state
            return (tty,st,fmap snd xs,fmap snd greedy)
    let arrivals   = new_users \\ known_users
        departures = known_users \\ new_users
    update_presence greedy subs departures $ const Offline
    update_presence greedy subs arrivals   $ matchResource tty

on_chvt state vtnum = do
    let tty = L.snoc "tty" $ intToDigit (fromIntegral vtnum)
    L.putStrLn $ "VT switch: " <++> tty
    (users,subs,greedy) <- atomically $ do
        us   <- readTVar $ activeUsers state
        subs <- readTVar $ subscriberMap state
        writeTVar (currentTTY state) tty
        greedy <- tryReadTMVar $ greedySubscriber state
        return (us,fmap snd subs,fmap snd greedy)
    update_presence greedy subs users $ matchResource tty


start :: IO ()
start = do
    tracked <- newPresenceState
    let dologin e = track_login tracked e
        dologin :: t -> IO ()
    installHandler sigUSR1 (Catch (dologin (userError "signaled"))) Nothing
    -- installHandler sigTERM (CatchOnce (dologin (userError "term signaled"))) Nothing
    mtty <- monitorTTY (on_chvt tracked)
    inotify <- initINotify
#ifndef NOUTMP
    wd <- addWatch
            inotify
            [CloseWrite] -- [Open,Close,Access,Modify,Move]
            utmp_file
            dologin
#endif
    sock <- listenForXmppClients (UnixSessions tracked) 5222 HNil

    threadDelay 1000 -- wait a moment to obtain current tty
    dologin ()
    putStrLn "\nHit enter to terminate...\n"
    getLine
    sClose sock
    -- threadDelay 1000
    putStrLn "closed listener."
    unmonitorTTY mtty
    putStrLn "unhooked tty monitor."
#ifndef NOUTMP
    removeWatch wd
#endif
    putStrLn "Normal termination."

sendUSR1 pid = do
    signalProcess sigUSR1 pid

getStartupAction []     = throw (userError "pid file?") >> return (Right "")
getStartupAction (p:ps) = do
    handle onEr $
        ( do
            pid <- fmap CPid (readFile p >>= readIO)
            -- signal pid
            return (Left pid) )
 where
    onEr (SomeException _) = do
        pid <- getProcessID
        putStrLn $ "starting pid = " <++> bshow pid
        handle (\(SomeException _) -> getStartupAction ps)
            (do 
                writeFile p (show pid)
                putStrLn $ "writing " <++> bshow p
                -- start daemon
                return (Right p) )

runOnce ps run notify = getStartupAction ps >>= doit
 where
    doit (Left pid      ) = notify pid
    doit (Right pidfile ) = do 
        run
        removeFile pidfile


main = do
    runOnce ["/var/run/presence.pid","/tmp/presence.pid"] start sendUSR1