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

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

import Blaze.ByteString.Builder (Builder)
import qualified Control.Exception as E (SomeException, IOException, try, catch)
import Control.Monad (when)
import Data.ByteString (ByteString)
import qualified Data.ByteString.Char8 as BS (readInt, unpack, tail)
import Data.Conduit
import qualified Data.Conduit.Binary as CB
import qualified Data.Conduit.List as CL
import Network.HTTP.Types
import Network.SockAddr
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 System.Environment
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 -> CgiAppSpec -> CgiRoute -> Application
cgiApp cspec spec cgii req = case method of
    Right GET  -> cgiApp' False cspec spec cgii req
    Right POST -> cgiApp' True  cspec spec cgii req
    _          -> return $ responseLBS methodNotAllowed405 textPlainHeader "Method Not Allowed\r\n" -- xxx
  where
    method = parseMethod $ requestMethod req

cgiApp' :: Bool -> ClassicAppSpec -> CgiAppSpec -> CgiRoute -> Application
cgiApp' body cspec spec cgii req = responseSourceBracket setup teardown cgi
  where
    setup = execProcess cspec spec cgii req
    teardown (rhdl,whdl,pid) = do
        terminateProcess pid -- SIGTERM
        hClose rhdl
        hClose whdl
    cgi (rhdl,whdl,_) = do
        when body $ toCGI whdl req
        hClose whdl -- telling EOF
        fromCGI rhdl cspec req

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

type TRYPATH = Either E.IOException String

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

fromCGI :: Handle -> ClassicAppSpec -> Request -> IO (Status, RequestHeaders, Source IO (Flush Builder))
fromCGI rhdl cspec req = do
    (src', hs) <- cgiHeader `E.catch` recover
    let (st, hdr, hasBody) = case check hs of
            Nothing    -> (internalServerError500,[],False)
            Just (s,h) -> (s,h,True)
        hdr' = addServer cspec hdr
    logger cspec req st Nothing
    let src | hasBody   = src'
            | otherwise = CL.sourceNull
    return (st, hdr', src)
  where
    check hs = lookup hContentType hs >> case lookup hStatus hs of
        Nothing -> Just (ok200, hs)
        Just l  -> toStatus l >>= \s -> Just (s,hs')
      where
        hs' = filter (\(k,_) -> k /= hStatus) hs
    toStatus s = BS.readInt s >>= \x -> Just (Status (fst x) s)
    emptyHeader = []
    recover (_ :: E.SomeException) = return (CL.sourceNull, emptyHeader)
    cgiHeader = do
        (rsrc,hs) <- CB.sourceHandle rhdl $$+ parseHeader
        src <- toResponseSource rsrc
        return (src,hs)

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

execProcess :: ClassicAppSpec -> CgiAppSpec -> CgiRoute -> Request -> IO (Handle, Handle, ProcessHandle)
execProcess cspec spec cgii req = do
    let naddr = showSockAddr . remoteHost $ req
    epath <- E.try (getEnv "PATH") :: IO TRYPATH
    (Just whdl,Just rhdl,_,pid) <- createProcess $ proSpec naddr epath
    hSetEncoding rhdl latin1
    hSetEncoding whdl latin1
    return (rhdl, whdl, pid)
 where
    proSpec naddr epath = CreateProcess {
        cmdspec = RawCommand prog []
      , cwd = Nothing
      , env = Just $ makeEnv req naddr scriptName pathinfo (softwareName cspec) epath
      , std_in = CreatePipe
      , std_out = CreatePipe
      , std_err = Inherit
      , close_fds = True
#if __GLASGOW_HASKELL__ >= 702
      , create_group = True
#endif
#if __GLASGOW_HASKELL__ >= 707
      , delegate_ctlc = False
#endif
      }
    (prog, scriptName, pathinfo) =
        pathinfoToCGI (cgiSrc cgii)
                      (cgiDst cgii)
                      (fromByteString (rawPathInfo req))
                      (indexCgi spec)

makeEnv :: Request -> String -> String -> String -> ByteString ->
           TRYPATH -> ENVVARS
makeEnv req naddr scriptName pathinfo sname epath = addPath epath . addLen . addType . addCookie $ baseEnv
  where
    baseEnv = [
        ("GATEWAY_INTERFACE", gatewayInterface)
      , ("SCRIPT_NAME",       scriptName)
      , ("REQUEST_METHOD",    BS.unpack . requestMethod $ req)
      , ("SERVER_NAME",       BS.unpack host)
      , ("SERVER_PORT",       BS.unpack port)
      , ("REMOTE_ADDR",       naddr)
      , ("SERVER_PROTOCOL",   show . httpVersion $ req)
      , ("SERVER_SOFTWARE",   BS.unpack sname)
      , ("PATH_INFO",         pathinfo)
      , ("QUERY_STRING",      query req)
      ]
    headers = requestHeaders req
    addLen    = addLength "CONTENT_LENGTH" $ requestBodyLength req
    addType   = addEnv "CONTENT_TYPE"   $ lookup hContentType   headers
    addCookie = addEnv "HTTP_COOKIE"    $ lookup hCookie        headers
    addPath (Left _)     ev = ev
    addPath (Right path) ev = ("PATH", path) : ev
    query = BS.unpack . safeTail . rawQueryString
      where
        safeTail "" = ""
        safeTail bs = BS.tail bs
    (host, port) = hostPort req

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

addLength :: String -> RequestBodyLength -> ENVVARS -> ENVVARS
addLength _   ChunkedBody       envs = envs
addLength key (KnownLength len) envs = (key, show len) : envs

{-|

>>> pathinfoToCGI "/cgi-bin/" "/User/cgi-bin/" "/cgi-bin/foo" "index.cgi"
("/User/cgi-bin/foo","/cgi-bin/foo","")
>>> pathinfoToCGI "/cgi-bin/" "/User/cgi-bin/" "/cgi-bin/foo/bar" "index.cgi"
("/User/cgi-bin/foo","/cgi-bin/foo","/bar")
>>> pathinfoToCGI "/cgi-bin/" "/User/cgi-bin/" "/cgi-bin/" "index.cgi"
("/User/cgi-bin/index.cgi","/cgi-bin/index.cgi","")

-}

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