{- Yesod webapp
 -
 - Copyright 2012 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

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

module Utility.WebApp where

import Common
import Utility.Tmp
import Utility.FileMode

import qualified Yesod
import qualified Network.Wai as Wai
import Network.Wai.Handler.Warp
import Network.Wai.Logger
import Control.Monad.IO.Class
import Network.HTTP.Types
import System.Log.Logger
import qualified Data.CaseInsensitive as CI
import Network.Socket
import Control.Exception
import Crypto.Random
import Data.Digest.Pure.SHA
import qualified Web.ClientSession as CS
import qualified Data.ByteString.Lazy as L
import qualified Data.ByteString.Lazy.UTF8 as L8
import qualified Data.ByteString as B
import qualified Data.Text as T
import qualified Data.Text.Encoding as TE
import Blaze.ByteString.Builder.Char.Utf8 (fromText)
import Blaze.ByteString.Builder (Builder)
import Data.Monoid
import Control.Arrow ((***))
import Control.Concurrent
#ifdef __ANDROID__
import Data.Endian
#endif

localhost :: HostName
localhost = "localhost"

{- Builds a command to use to start or open a web browser showing an url. -}
browserProc :: String -> CreateProcess
#ifdef darwin_HOST_OS
browserProc url = proc "open" [url]
#else
#ifdef __ANDROID__
-- Warning: The `am` command does not work very reliably on Android.
browserProc url = proc "am"
	["start", "-a", "android.intent.action.VIEW", "-d", url]
#else
browserProc url = proc "xdg-open" [url]
#endif
#endif

{- Binds to a socket on localhost, or possibly a different specified
 - hostname or address, and runs a webapp on it.
 -
 - An IO action can also be run, to do something with the address,
 - such as start a web browser to view the webapp.
 -}
runWebApp :: Maybe HostName -> Wai.Application -> (SockAddr -> IO ()) -> IO ()
runWebApp h app observer = do
	sock <- getSocket h
	void $ forkIO $ runSettingsSocket webAppSettings sock app
	sockaddr <- fixSockAddr <$> getSocketName sock
	observer sockaddr

fixSockAddr :: SockAddr -> SockAddr
#ifdef __ANDROID__
{- On Android, the port is currently incorrectly returned in network
 - byte order, which is wrong on little endian systems. -}
fixSockAddr (SockAddrInet (PortNum port) addr) = SockAddrInet (PortNum $ swapEndian port) addr
#endif
fixSockAddr addr = addr

webAppSettings :: Settings
webAppSettings = defaultSettings
	-- disable buggy sloworis attack prevention code
	{ settingsTimeout = 30 * 60
	}

{- Binds to a local socket, or if specified, to a socket on the specified
 - hostname or address. Selects any free port, unless the hostname ends with
 - ":port"
 -
 - Prefers to bind to the ipv4 address rather than the ipv6 address
 - of localhost, if it's available.
 -}
getSocket :: Maybe HostName -> IO Socket
getSocket h = do
#ifdef __ANDROID__
	-- getAddrInfo currently segfaults on Android.
	-- The HostName is ignored by this code.
	when (isJust h) $
		error "getSocket with HostName not supported on Android"
	addr <- inet_addr "127.0.0.1"
 	sock <- socket AF_INET Stream defaultProtocol
	preparesocket sock
	bindSocket sock (SockAddrInet aNY_PORT addr)
	use sock
  where
#else
	addrs <- getAddrInfo (Just hints) (Just hostname) port
	case (partition (\a -> addrFamily a == AF_INET) addrs) of
		(v4addr:_, _) -> go v4addr
		(_, v6addr:_) -> go v6addr
		_ -> error "unable to bind to a local socket"
  where
	(hostname, port) = maybe (localhost, Nothing) splitHostPort h
	hints = defaultHints { addrSocketType = Stream }
	{- Repeated attempts because bind sometimes fails for an
	 - unknown reason on OSX. -} 
	go addr = go' 100 addr
	go' :: Int -> AddrInfo -> IO Socket
	go' 0 _ = error "unable to bind to local socket"
	go' n addr = do
		r <- tryIO $ bracketOnError (open addr) sClose (useaddr addr)
		either (const $ go' (pred n) addr) return r
	open addr = socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr)
	useaddr addr sock = do
		preparesocket sock
		bindSocket sock (addrAddress addr)
		use sock
#endif
	preparesocket sock = setSocketOption sock ReuseAddr 1
	use sock = do
		listen sock maxListenQueue
		return sock

{- Splits address:port. For IPv6, use [address]:port. The port is optional. -}
splitHostPort :: String -> (HostName, Maybe ServiceName)
splitHostPort s
	| "[" `isPrefixOf` s = let (h, p) = break (== ']') (drop 1 s)
		in if "]:" `isPrefixOf` p
			then (h, Just $ drop 2 p)
			else (h, Nothing)
	| otherwise = let (h, p) = separate (== ':') s
		in if null p
			then (h, Nothing)
			else (h, Just p)

{- Checks if debugging is actually enabled. -}
debugEnabled :: IO Bool
debugEnabled = do
	l <- getRootLogger
	return $ getLevel l <= Just DEBUG

{- WAI middleware that logs using System.Log.Logger at debug level.
 -
 - Recommend only inserting this middleware when debugging is actually
 - enabled, as it's not optimised at all.
 -}
httpDebugLogger :: Wai.Middleware
httpDebugLogger waiApp req = do
	logRequest req
	waiApp req

logRequest :: MonadIO m => Wai.Request -> m ()
logRequest req = do
	liftIO $ debugM "WebApp" $ unwords
		[ showSockAddr $ Wai.remoteHost req
		, frombs $ Wai.requestMethod req
		, frombs $ Wai.rawPathInfo req
		--, show $ Wai.httpVersion req
		--, frombs $ lookupRequestField "referer" req
		, frombs $ lookupRequestField "user-agent" req
		]
  where
	frombs v = L8.toString $ L.fromChunks [v]

lookupRequestField :: CI.CI B.ByteString -> Wai.Request -> B.ByteString
lookupRequestField k req = fromMaybe "" . lookup k $ Wai.requestHeaders req

{- Rather than storing a session key on disk, use a random key
 - that will only be valid for this run of the webapp. -}
#if MIN_VERSION_yesod(1,2,0)
webAppSessionBackend :: Yesod.Yesod y => y -> IO (Maybe Yesod.SessionBackend)
#else
webAppSessionBackend :: Yesod.Yesod y => y -> IO (Maybe (Yesod.SessionBackend y))
#endif
webAppSessionBackend _ = do
	g <- newGenIO :: IO SystemRandom
	case genBytes 96 g of
		Left e -> error $ "failed to generate random key: " ++ show e
		Right (s, _) -> case CS.initKey s of
			Left e -> error $ "failed to initialize key: " ++ show e
			Right key -> use key
  where
	timeout = 120 * 60 -- 120 minutes
	use key =
#if MIN_VERSION_yesod(1,2,0)
		Just . Yesod.clientSessionBackend key . fst
			<$> Yesod.clientSessionDateCacher timeout
#else
#if MIN_VERSION_yesod(1,1,7)
		Just . Yesod.clientSessionBackend2 key . fst
			<$> Yesod.clientSessionDateCacher timeout
#else
		return $ Just $
			Yesod.clientSessionBackend key timeout
#endif
#endif

{- Generates a random sha512 string, suitable to be used for an
 - authentication secret. -}
genRandomToken :: IO String
genRandomToken = do
	g <- newGenIO :: IO SystemRandom
	return $
		case genBytes 512 g of
			Left e -> error $ "failed to generate secret token: " ++ show e
			Right (s, _) -> showDigest $ sha512 $ L.fromChunks [s]

{- A Yesod isAuthorized method, which checks the auth cgi parameter
 - against a token extracted from the Yesod application.
 -
 - Note that the usual Yesod error page is bypassed on error, to avoid
 - possibly leaking the auth token in urls on that page!
 -}
#if MIN_VERSION_yesod(1,2,0)
checkAuthToken :: (Monad m, Yesod.MonadHandler m) => (Yesod.HandlerSite m -> T.Text) -> m Yesod.AuthResult
#else
checkAuthToken :: forall t sub. (t -> T.Text) -> Yesod.GHandler sub t Yesod.AuthResult
#endif
checkAuthToken extractToken = do
	webapp <- Yesod.getYesod
	req <- Yesod.getRequest
	let params = Yesod.reqGetParams req
	if lookup "auth" params == Just (extractToken webapp)
		then return Yesod.Authorized
		else Yesod.sendResponseStatus unauthorized401 ()

{- A Yesod joinPath method, which adds an auth cgi parameter to every
 - url matching a predicate, containing a token extracted from the
 - Yesod application.
 - 
 - A typical predicate would exclude files under /static.
 -}
insertAuthToken :: forall y. (y -> T.Text)
	-> ([T.Text] -> Bool)
	-> y
	-> T.Text
	-> [T.Text]
	-> [(T.Text, T.Text)]
	-> Builder
insertAuthToken extractToken predicate webapp root pathbits params =
	fromText root `mappend` encodePath pathbits' encodedparams
  where
	pathbits' = if null pathbits then [T.empty] else pathbits
	encodedparams = map (TE.encodeUtf8 *** go) params'
	go "" = Nothing
	go x = Just $ TE.encodeUtf8 x
	authparam = (T.pack "auth", extractToken webapp)
	params'
		| predicate pathbits = authparam:params
		| otherwise = params

{- Creates a html shim file that's used to redirect into the webapp,
 - to avoid exposing the secret token when launching the web browser. -}
writeHtmlShim :: String -> String -> FilePath -> IO ()
writeHtmlShim title url file = viaTmp writeFileProtected file $ genHtmlShim title url

{- TODO: generate this static file using Yesod. -}
genHtmlShim :: String -> String -> String
genHtmlShim title url = unlines
	[ "<html>"
	, "<head>"
	, "<title>"++ title ++ "</title>"
	, "<meta http-equiv=\"refresh\" content=\"1; URL="++url++"\">"
	, "<body>"
	, "<p>"
	, "<a href=\"" ++ url ++ "\">" ++ title ++ "</a>"
	, "</p>"
	, "</body>"
	, "</html>"
	]