{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RankNTypes #-}
-- | Backend for Common Gateway Interface. Almost all users should use the
-- 'run' function.
module Network.Wai.Handler.CGI
    ( run
    , runSendfile
    , runGeneric
    , requestBodyFunc
    ) where

import Network.Wai
import Network.Socket (getAddrInfo, addrAddress)
import System.Environment (getEnvironment)
import Data.Maybe (fromMaybe)
import qualified Data.ByteString.Char8 as B
import qualified Data.ByteString.Lazy as L
import Control.Arrow ((***))
import Data.Char (toLower)
import qualified System.IO
import qualified Data.String as String
import Data.Enumerator
    ( Enumerator, Step (..), Stream (..), continue, yield
    , enumList, ($$), joinI, returnI, (>>==), run_
    )
import Data.Monoid (mconcat)
import Blaze.ByteString.Builder (fromByteString, toLazyByteString)
import Blaze.ByteString.Builder.Char8 (fromChar, fromString)
import Blaze.ByteString.Builder.Enumerator (builderToByteString)
import Control.Monad.IO.Class (liftIO)
import Data.ByteString.Lazy.Internal (defaultChunkSize)
import System.IO (Handle)
import Network.HTTP.Types (Status (..))
import qualified Network.HTTP.Types as H
import qualified Data.CaseInsensitive as CI

safeRead :: Read a => a -> String -> a
safeRead d s =
  case reads s of
    ((x, _):_) -> x
    [] -> d

lookup' :: String -> [(String, String)] -> String
lookup' key pairs = fromMaybe "" $ lookup key pairs

-- | Run an application using CGI.
run :: Application -> IO ()
run app = do
    vars <- getEnvironment
    let input = requestBodyHandle System.IO.stdin
        output = B.hPut System.IO.stdout
    runGeneric vars input output Nothing app

-- | Some web servers provide an optimization for sending files via a sendfile
-- system call via a special header. To use this feature, provide that header
-- name here.
runSendfile :: B.ByteString -- ^ sendfile header
            -> Application -> IO ()
runSendfile sf app = do
    vars <- getEnvironment
    let input = requestBodyHandle System.IO.stdin
        output = B.hPut System.IO.stdout
    runGeneric vars input output (Just sf) app

-- | A generic CGI helper, which allows other backends (FastCGI and SCGI) to
-- use the same code as CGI. Most users will not need this function, and can
-- stick with 'run' or 'runSendfile'.
runGeneric
     :: [(String, String)] -- ^ all variables
     -> (forall a. Int -> Enumerator B.ByteString IO a) -- ^ responseBody of input
     -> (B.ByteString -> IO ()) -- ^ destination for output
     -> Maybe B.ByteString -- ^ does the server support the X-Sendfile header?
     -> Application
     -> IO ()
runGeneric vars inputH outputH xsendfile app = do
    let rmethod = B.pack $ lookup' "REQUEST_METHOD" vars
        pinfo = lookup' "PATH_INFO" vars
        qstring = lookup' "QUERY_STRING" vars
        servername = lookup' "SERVER_NAME" vars
        serverport = safeRead 80 $ lookup' "SERVER_PORT" vars
        contentLength = safeRead 0 $ lookup' "CONTENT_LENGTH" vars
        remoteHost' =
            case lookup "REMOTE_ADDR" vars of
                Just x -> x
                Nothing ->
                    case lookup "REMOTE_HOST" vars of
                        Just x -> x
                        Nothing -> ""
        isSecure' =
            case map toLower $ lookup' "SERVER_PROTOCOL" vars of
                "https" -> True
                _ -> False
    addrs <- getAddrInfo Nothing (Just remoteHost') Nothing
    let addr =
            case addrs of
                a:_ -> addrAddress a
                [] -> error $ "Invalid REMOTE_ADDR or REMOTE_HOST: " ++ remoteHost'
    let env = Request
            { requestMethod = rmethod
            , rawPathInfo = B.pack pinfo
            , pathInfo = H.decodePathSegments $ B.pack pinfo
            , rawQueryString = B.pack qstring
            , queryString = H.parseQuery $ B.pack qstring
            , serverName = B.pack servername
            , serverPort = serverport
            , requestHeaders = map (cleanupVarName *** B.pack) vars
            , isSecure = isSecure'
            , remoteHost = addr
            , httpVersion = H.http11 -- FIXME
            }
    -- FIXME worry about exception?
    res <- run_ $ inputH contentLength $$ app env
    case (xsendfile, res) of
        (Just sf, ResponseFile s hs fp Nothing) ->
            mapM_ outputH $ L.toChunks $ toLazyByteString $ sfBuilder s hs sf fp
        _ -> responseEnumerator res $ \s hs ->
            joinI $ enumList 1 [headers s hs, fromChar '\n'] $$ builderIter
  where
    headers s hs = mconcat (map header $ status s : map header' (fixHeaders hs))
    status (Status i m) = (fromByteString "Status", mconcat
        [ fromString $ show i
        , fromChar ' '
        , fromByteString m
        ])
    header' (x, y) = (fromByteString $ CI.original x, fromByteString y)
    header (x, y) = mconcat
        [ x
        , fromByteString ": "
        , y
        , fromChar '\n'
        ]
    sfBuilder s hs sf fp = mconcat
        [ headers s hs
        , header $ (fromByteString sf, fromString fp)
        , fromChar '\n'
        , fromByteString sf
        , fromByteString " not supported"
        ]
    bsStep = Continue bsStep'
    bsStep' EOF = yield () EOF
    bsStep' (Chunks []) = continue bsStep'
    bsStep' (Chunks bss) = liftIO (mapM_ outputH bss) >> continue bsStep'
    builderIter = builderToByteString bsStep
    fixHeaders h =
        case lookup "content-type" h of
            Nothing -> ("Content-Type", "text/html; charset=utf-8") : h
            Just _ -> h

cleanupVarName :: String -> CI.CI B.ByteString
cleanupVarName "CONTENT_TYPE" = "Content-Type"
cleanupVarName "CONTENT_LENGTH" = "Content-Length"
cleanupVarName "SCRIPT_NAME" = "CGI-Script-Name"
cleanupVarName s =
    case s of
        'H':'T':'T':'P':'_':a:as -> String.fromString $ a : helper' as
        _ -> String.fromString s -- FIXME remove?
  where
    helper' ('_':x:rest) = '-' : x : helper' rest
    helper' (x:rest) = toLower x : helper' rest
    helper' [] = []

requestBodyHandle :: Handle -> Int -> Enumerator B.ByteString IO a
requestBodyHandle h =
    requestBodyFunc go
  where
    go i = Just `fmap` B.hGet h (min i defaultChunkSize)

requestBodyFunc :: (Int -> IO (Maybe B.ByteString))
                -> Int
                -> Enumerator B.ByteString IO a
requestBodyFunc _ 0 step = returnI step
requestBodyFunc h len (Continue k) = do
    mbs <- liftIO $ h len
    case mbs of
        Nothing -> continue k
        Just bs -> do
            let newLen = len - B.length bs
            k (Chunks [bs]) >>== requestBodyFunc h newLen
requestBodyFunc _ _ step = returnI step