{-# OPTIONS_HADDOCK ignore-exports #-}
-- |The Clients module in the PupEvents framework is used by the main
-- application code to send events to the server. Its main function,
-- 'client' returns a pair of "PQueues" that the application uses to send
-- and receive events (written following the specification defined in the
-- Events module).
module PupEventsClient (client) where

import Network.Socket
import System.IO
import Control.Concurrent
import Control.Concurrent.STM
import Control.Monad
import Text.Parsec
import PupEventsPQueue
import Data.Functor.Identity

-- |The client function is the main entry point for the client code. It creates a socket, spawns two processes ('sendEvents' and 'recvEvents') to handle outgoing and incoming events, and returns the queues used to communicate with those processes.
client ::   Maybe [Char] -- ^ The address to connect to. If ommitted we connect to 'localhost'
            -> Int -- ^ The number of priorities in the PQueue
            -> (a -> Int) -- ^ A function to return the priority level of an event
            -> (t -> t -> String) -- ^ A function to return the string representation of an event
            -> [ParsecT [Char] () Data.Functor.Identity.Identity a] -- ^ A list of parsers that return Event objects
            -> IO (PQueue t, PQueue a) -- ^ We return a pair of "PQueues" to use in communicating events. The first is for all events going to the server, the second is for events coming from the server.
client Nothing priorities lookupPriority lookupUnHandler parsers = client (Just "localhost") priorities lookupPriority lookupUnHandler parsers
client ip priorities lookupPriority lookupUnHandler parsers=
    -- get address info
    do  addrinfos <- getAddrInfo Nothing ip (Just "1267")
        let serveraddr = head addrinfos
        -- create socket
        sock <- socket (addrFamily serveraddr) Stream 6
        setSocketOption sock KeepAlive 1
        -- connect to the server
        connect sock (addrAddress serveraddr)
        -- convert to handle for convenience
        handle <- socketToHandle sock ReadWriteMode
        hSetBuffering handle NoBuffering
        -- create pqueue
        outqueue <- makeQueues priorities
        inqueue <- makeQueues priorities
        -- fork communication threads to server
        forkOS $ sendEvents handle outqueue lookupUnHandler
        forkOS $ recvEvents handle inqueue lookupPriority parsers
        -- outqueue is the outgoing messages to the server
        -- inqueue is the incoming messages from the server
        return (outqueue, inqueue)

-- |The sendEvents function handles the sending of all outgoing events to the server. It checks for an event, blocks if none is available, and sends it.
sendEvents ::   Handle -- ^ Handle to send events on
                -> PQueue t -- ^ "PQueue" to listen on
                -> (t -> t -> String) -- ^ A function to convert an Event to a string
                -> IO b
sendEvents handle pqueue lookupUnHandler = forever $
    do  event <- atomically $
            do  e <- getThing pqueue
                case e of
                    Nothing -> retry
                    Just event -> return event
        hPutStr handle (lookupUnHandler event event)
        hFlush handle

-- |The recvEvents function receives events until the connection is closed, parses them, and puts them on the queue to be handled by the application.
recvEvents ::   Handle -- ^ Handle listen on
                -> PQueue a -- ^ "PQueue" to send events on
                -> (a -> Int) -- ^ Function to lookup the priority level of an event
                -> [ParsecT [Char] () Data.Functor.Identity.Identity a] -- ^ A list of parsers to apply to parse an event
                -> IO ()
recvEvents handle pqueue lookupPriority parsers =
    -- I don't really understand how these two lines work, but I think its
    -- got something to do with lazy evalution.  they're from RWH.
    do  messages <- hGetContents handle
        mapM_ toDispatch (nullLines messages)
        hClose handle
        -- |Attempts to parse an event and send it to the queue.
        toDispatch str = 
            case parse parseMsg "" str of
                Left e -> putStrLn $ "ParseError: " ++ show e ++ "\nString: " ++ show str
                Right event ->  atomically $ writeThing pqueue (lookupPriority event) event

        -- |Applies the parsers given in 'client' until one of them succeeds.
        parseMsg =  choice parsers
        -- |Separates a string on the character sequence \"\0\0\"
        nullLines "" = []
        nullLines str = x:nullLines xs
            where   (x, xs) = splitAt (nullLines' 0 str) str
                    nullLines' n [] = n
                    nullLines' n ('\0':'\0':str) = n+2
                    nullLines' n (s:str) = nullLines' (n+1) str