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

module Network.Wai.Application.Classic.CGI (
    cgiApp
  ) where

import Control.Applicative
import Control.Exception (SomeException)
import Control.Exception.Lifted (catch)
import Control.Monad (when)
import Control.Monad.IO.Class (liftIO)
import Control.Monad.Trans.Resource
import Data.ByteString (ByteString)
import qualified Data.ByteString as BS hiding (unpack)
import qualified Data.ByteString.Char8 as BS (readInt, unpack)
import Data.Conduit
import qualified Data.Conduit.Binary as CB
import qualified Data.Conduit.List as CL
import Network.HTTP.Types
import Network.Wai
import Network.Wai.Application.Classic.Conduit
import Network.Wai.Application.Classic.Field
import Network.Wai.Application.Classic.Header
import Network.Wai.Application.Classic.Path
import Network.Wai.Application.Classic.Types
import Network.Wai.Logger.Utils
import Prelude hiding (catch)
import System.IO
import System.Process

----------------------------------------------------------------

type ENVVARS = [(String,String)]

gatewayInterface :: String
gatewayInterface = "CGI/1.1"

----------------------------------------------------------------

{-|
  Handle GET and POST for CGI.

The program to link this library must ignore SIGCHLD as follows:

>   installHandler sigCHLD Ignore Nothing
-}
cgiApp :: ClassicAppSpec -> CgiRoute -> Application
cgiApp cspec cgii req = case method of
    "GET"  -> cgiApp' False cspec cgii req
    "POST" -> cgiApp' True  cspec cgii req
    _      -> return $ responseLBS statusNotAllowed textPlainHeader "Method Not Allowed\r\n" -- xxx
  where
    method = requestMethod req

cgiApp' :: Bool -> ClassicAppSpec -> CgiRoute -> Application
cgiApp' body cspec cgii req = do
    (rhdl,whdl,tellEOF) <- liftIO (execProcess cspec cgii req) >>= register3
    when body $ toCGI whdl req
    tellEOF
    fromCGI rhdl cspec req
  where
    register3 (rhdl,whdl,pid) = do
        register $ terminateProcess pid -- SIGTERM
        register $ hClose rhdl
        keyw <- register $ hClose whdl
        return (rhdl,whdl,release keyw)

----------------------------------------------------------------

toCGI :: Handle -> Request -> ResourceT IO ()
toCGI whdl req = requestBody req $$ CB.sinkHandle whdl

fromCGI :: Handle -> ClassicAppSpec -> Application
fromCGI rhdl cspec req = do
    bsrc <- bufferSource $ CB.sourceHandle rhdl
    m <- (check <$> (bsrc $$ parseHeader)) `catch` recover
    let (st, hdr, hasBody) = case m of
            Nothing    -> (statusServerError,[],False)
            Just (s,h) -> (s,h,True)
        hdr' = addServer cspec hdr
    liftIO $ logger cspec req st Nothing
    let src = if hasBody then toSource bsrc else CL.sourceNull
    return $ ResponseSource st hdr' (Chunk <$> src)
  where
    check hs = lookup fkContentType hs >> case lookup "status" hs of
        Nothing -> Just (status200, hs)
        Just l  -> toStatus l >>= \s -> Just (s,hs')
      where
        hs' = filter (\(k,_) -> k /= "status") hs
    toStatus s = BS.readInt s >>= \x -> Just (Status (fst x) s)
    recover (_ :: SomeException) = return Nothing

----------------------------------------------------------------

execProcess :: ClassicAppSpec -> CgiRoute -> Request -> IO (Handle, Handle, ProcessHandle)
execProcess cspec cgii req = do
    let naddr = showSockAddr . remoteHost $ req
    (Just whdl,Just rhdl,_,pid) <- createProcess . proSpec $ naddr
    hSetEncoding rhdl latin1
    hSetEncoding whdl latin1
    return (rhdl, whdl, pid)
 where
    proSpec naddr = CreateProcess {
        cmdspec = RawCommand prog []
      , cwd = Nothing
      , env = Just (makeEnv req naddr scriptName pathinfo (softwareName cspec))
      , std_in = CreatePipe
      , std_out = CreatePipe
      , std_err = Inherit
      , close_fds = True
#if __GLASGOW_HASKELL__ >= 702
      , create_group = True
#endif
      }
    (prog, scriptName, pathinfo) = pathinfoToCGI (cgiSrc cgii)
                                                 (cgiDst cgii)
                                                 (fromByteString (rawPathInfo req))

makeEnv :: Request -> NumericAddress -> String -> String -> ByteString -> ENVVARS
makeEnv req naddr scriptName pathinfo sname = addLen . addType . addCookie $ baseEnv
  where
    baseEnv = [
        ("GATEWAY_INTERFACE", gatewayInterface)
      , ("SCRIPT_NAME",       scriptName)
      , ("REQUEST_METHOD",    BS.unpack . requestMethod $ req)
      , ("SERVER_NAME",       BS.unpack . serverName $ req)
      , ("SERVER_PORT",       show . serverPort $ req)
      , ("REMOTE_ADDR",       naddr)
      , ("SERVER_PROTOCOL",   show . httpVersion $ req)
      , ("SERVER_SOFTWARE",   BS.unpack sname)
      , ("PATH_INFO",         pathinfo)
      , ("QUERY_STRING",      query req)
      ]
    headers = requestHeaders req
    addLen = addEnv "CONTENT_LENGTH" $ lookup fkContentLength headers
    addType   = addEnv "CONTENT_TYPE" $ lookup fkContentType headers
    addCookie = addEnv "HTTP_COOKIE" $ lookup fkCookie headers
    query = BS.unpack . safeTail . rawQueryString
      where
        safeTail "" = ""
        safeTail bs = BS.tail bs

addEnv :: String -> Maybe ByteString -> ENVVARS -> ENVVARS
addEnv _   Nothing    envs = envs
addEnv key (Just val) envs = (key,BS.unpack val) : envs

pathinfoToCGI :: Path -> Path -> Path -> (FilePath, String, String)
pathinfoToCGI src dst path = (prog, scriptName, pathinfo)
  where
    path' = path <\> src
    (prog',pathinfo') = breakAtSeparator path'
    prog = pathString (dst </> prog')
    scriptName = pathString (src </> prog')
    pathinfo = pathString pathinfo'