{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE QuasiQuotes #-}

module Sproxy.Application
  ( sproxy
  , redirect
  ) where

import Blaze.ByteString.Builder (toByteString)
import Blaze.ByteString.Builder.ByteString (fromByteString)
import Control.Exception
       (Exception, Handler(..), SomeException, catches, displayException)
import qualified Data.Aeson as JSON
import Data.ByteString (ByteString)
import qualified Data.ByteString as BS
import Data.ByteString.Char8 (pack, unpack)
import Data.ByteString.Lazy (fromStrict)
import Data.Conduit (Flush(Chunk), mapOutput)
import qualified Data.HashMap.Strict as HM
import Data.List (find, partition)
import Data.Maybe (fromJust, fromMaybe)
import Data.Monoid ((<>))
import Data.Text (Text)
import Data.Text.Encoding (decodeUtf8, encodeUtf8)
import Data.Time.Clock.POSIX (posixSecondsToUTCTime)
import Data.Word (Word16)
import Data.Word8 (_colon)
import Foreign.C.Types (CTime(..))
import qualified Network.HTTP.Client as BE
import Network.HTTP.Client.Conduit (bodyReaderSource)
import Network.HTTP.Conduit
       (requestBodySourceChunkedIO, requestBodySourceIO)
import Network.HTTP.Types
       (RequestHeaders, ResponseHeaders, methodGet, methodPost)
import Network.HTTP.Types.Header
       (hConnection, hContentLength, hContentType, hCookie, hLocation,
        hTransferEncoding)
import Network.HTTP.Types.Status
       (Status(..), badGateway502, badRequest400, forbidden403, found302,
        internalServerError500, methodNotAllowed405, movedPermanently301,
        networkAuthenticationRequired511, notFound404, ok200, seeOther303,
        temporaryRedirect307)
import Network.Socket (NameInfoFlag(NI_NUMERICHOST), getNameInfo)
import qualified Network.Wai as W
import Network.Wai.Conduit (responseSource, sourceRequestBody)
import System.FilePath.Glob (Pattern, match)
import System.Posix.Time (epochTime)
import Text.InterpolatedString.Perl6 (qc)
import Web.Cookie (Cookies, parseCookies, renderCookies)
import qualified Web.Cookie as WC

import Sproxy.Application.Cookie
       (AuthCookie(..), AuthUser, cookieDecode, cookieEncode, getEmail,
        getEmailUtf8, getFamilyNameUtf8, getGivenNameUtf8)
import Sproxy.Application.OAuth2.Common (OAuth2Client(..))
import qualified Sproxy.Application.State as State
import Sproxy.Config (BackendConf(..))
import qualified Sproxy.Logging as Log
import Sproxy.Server.DB
       (Database, userAccess, userExists, userGroups)

redirect :: Word16 -> W.Application
redirect p req resp =
  case requestDomain req of
    Nothing -> badRequest "missing host" req resp
    Just domain -> do
      Log.info $ "redirecting to " ++ show location ++ ": " ++ showReq req
      resp $ W.responseBuilder status [(hLocation, location)] mempty
      where status =
              if W.requestMethod req == methodGet
                then movedPermanently301
                else temporaryRedirect307
            newhost =
              if p == 443
                then domain
                else domain <> ":" <> pack (show p)
            location =
              "https://" <> newhost <> W.rawPathInfo req <> W.rawQueryString req

sproxy ::
     ByteString
  -> Database
  -> HM.HashMap Text OAuth2Client
  -> [(Pattern, BackendConf, BE.Manager)]
  -> W.Application
sproxy key db oa2 backends =
  logException $ \req resp -> do
    Log.debug $ "sproxy <<< " ++ showReq req
    case requestDomain req of
      Nothing -> badRequest "missing host" req resp
      Just domain ->
        case find (\(p, _, _) -> match p (unpack domain)) backends of
          Nothing -> notFound "backend" req resp
          Just (_, be, mgr) -> do
            let cookieName = pack $ beCookieName be
                cookieDomain = pack <$> beCookieDomain be
            case W.pathInfo req of
              ["robots.txt"] -> get robots req resp
              (".sproxy":proxy) ->
                case proxy of
                  ["logout"] ->
                    get (logout key cookieName cookieDomain) req resp
                  ["oauth2", provider] ->
                    case HM.lookup provider oa2 of
                      Nothing -> notFound "OAuth2 provider" req resp
                      Just oa2c ->
                        get (oauth2callback key db (provider, oa2c) be) req resp
                  ["access"] -> do
                    now <- Just <$> epochTime
                    case extractCookie key now cookieName req of
                      Nothing -> authenticationRequired key oa2 req resp
                      Just (authCookie, _) ->
                        post (checkAccess db authCookie) req resp
                  _ -> notFound "proxy" req resp
              _ -> do
                now <- Just <$> epochTime
                case extractCookie key now cookieName req of
                  Nothing -> authenticationRequired key oa2 req resp
                  Just cs@(authCookie, _) ->
                    authorize db cs req >>= \case
                      Nothing -> forbidden authCookie req resp
                      Just req' -> forward mgr req' resp

robots :: W.Application
robots _ resp =
  resp $
  W.responseLBS
    ok200
    [(hContentType, "text/plain; charset=utf-8")]
    "User-agent: *\nDisallow: /"

oauth2callback ::
     ByteString
  -> Database
  -> (Text, OAuth2Client)
  -> BackendConf
  -> W.Application
oauth2callback key db (provider, oa2c) be req resp =
  case param "code" of
    Nothing -> badRequest "missing auth code" req resp
    Just code ->
      case param "state" of
        Nothing -> badRequest "missing auth state" req resp
        Just state ->
          case State.decode key state of
            Left msg -> badRequest ("invalid state: " ++ msg) req resp
            Right url -> do
              au <- oauth2Authenticate oa2c code (redirectURL req provider)
              let email = getEmail au
              Log.info $ "login " ++ show email ++ " by " ++ show provider
              exists <- userExists db email
              if exists
                then authenticate key be au url req resp
                else userNotFound au req resp
  where
    param p = do
      (_, v) <- find ((==) p . fst) $ W.queryString req
      v

-- XXX: RFC6265: the user agent MUST NOT attach more than one Cookie header field
extractCookie ::
     ByteString
  -> Maybe CTime
  -> ByteString
  -> W.Request
  -> Maybe (AuthCookie, Cookies)
extractCookie key now name req = do
  (_, cookies) <- find ((==) hCookie . fst) $ W.requestHeaders req
  (auth, others) <- discriminate cookies
  case cookieDecode key auth of
    Left _ -> Nothing
    Right cookie ->
      if maybe True (acExpiry cookie >) now
        then Just (cookie, others)
        else Nothing
  where
    discriminate cs =
      case partition ((==) name . fst) $ parseCookies cs of
        ((_, x):_, xs) -> Just (x, xs)
        _ -> Nothing

authenticate ::
     ByteString -> BackendConf -> AuthUser -> ByteString -> W.Application
authenticate key be user url _req resp = do
  now <- epochTime
  let domain = pack <$> beCookieDomain be
      expiry = now + CTime (beCookieMaxAge be)
      authCookie = AuthCookie {acUser = user, acExpiry = expiry}
      cookie =
        WC.def
        { WC.setCookieName = pack $ beCookieName be
        , WC.setCookieHttpOnly = True
        , WC.setCookiePath = Just "/"
        , WC.setCookieSameSite = Nothing
        , WC.setCookieSecure = True
        , WC.setCookieValue = cookieEncode key authCookie
        , WC.setCookieDomain = domain
        , WC.setCookieExpires =
            Just . posixSecondsToUTCTime . realToFrac $ expiry
        }
  resp $
    W.responseLBS
      seeOther303
      [ (hLocation, url)
      , ("Set-Cookie", toByteString $ WC.renderSetCookie cookie)
      ]
      ""

authorize ::
     Database -> (AuthCookie, Cookies) -> W.Request -> IO (Maybe W.Request)
authorize db (authCookie, otherCookies) req = do
  let user = acUser authCookie
      domain = decodeUtf8 . fromJust $ requestDomain req
      email = getEmail user
      emailUtf8 = getEmailUtf8 user
      familyUtf8 = getFamilyNameUtf8 user
      givenUtf8 = getGivenNameUtf8 user
      method = decodeUtf8 $ W.requestMethod req
      path = decodeUtf8 $ W.rawPathInfo req
  grps <- userGroups db email domain path method
  if null grps
    then return Nothing
    else do
      ip <-
        pack . fromJust . fst <$>
        getNameInfo [NI_NUMERICHOST] True False (W.remoteHost req)
      return . Just $
        req
        { W.requestHeaders =
            HM.toList $
            HM.insert "From" emailUtf8 $
            HM.insert "X-Groups" (BS.intercalate "," $ encodeUtf8 <$> grps) $
            HM.insert "X-Given-Name" givenUtf8 $
            HM.insert "X-Family-Name" familyUtf8 $
            HM.insert "X-Forwarded-Proto" "https" $
            HM.insertWith (flip combine) "X-Forwarded-For" ip $
            setCookies otherCookies $
            HM.fromListWith combine $ W.requestHeaders req
        }
  where
    combine a b = a <> "," <> b
    setCookies [] = HM.delete hCookie
    setCookies cs = HM.insert hCookie (toByteString . renderCookies $ cs)

checkAccess :: Database -> AuthCookie -> W.Application
checkAccess db authCookie req resp = do
  let email = getEmail . acUser $ authCookie
      domain = decodeUtf8 . fromJust $ requestDomain req
  body <- W.strictRequestBody req
  case JSON.eitherDecode' body of
    Left err -> badRequest err req resp
    Right inq -> do
      Log.debug $ "access <<< " ++ show inq
      tags <- userAccess db email domain inq
      Log.debug $ "access >>> " ++ show tags
      resp $
        W.responseLBS
          ok200
          [(hContentType, "application/json")]
          (JSON.encode tags)

-- XXX If something seems strange, think about HTTP/1.1 <-> HTTP/1.0.
-- FIXME For HTTP/1.0 backends we might need an option
-- FIXME in config file. HTTP Client does HTTP/1.1 by default.
forward :: BE.Manager -> W.Application
forward mgr req resp = do
  let beReq =
        BE.defaultRequest
        { BE.method = W.requestMethod req
        , BE.path = W.rawPathInfo req
        , BE.queryString = W.rawQueryString req
        , BE.requestHeaders = modifyRequestHeaders $ W.requestHeaders req
        , BE.redirectCount = 0
        , BE.decompress = const False
        , BE.requestBody =
            case W.requestBodyLength req of
              W.ChunkedBody ->
                requestBodySourceChunkedIO (sourceRequestBody req)
              W.KnownLength l ->
                requestBodySourceIO (fromIntegral l) (sourceRequestBody req)
        }
      msg =
        unpack (BE.method beReq <> " " <> BE.path beReq <> BE.queryString beReq)
  Log.debug $ "BACKEND <<< " ++ msg ++ " " ++ show (BE.requestHeaders beReq)
  BE.withResponse beReq mgr $ \res -> do
    let status = BE.responseStatus res
        headers = BE.responseHeaders res
        body =
          mapOutput (Chunk . fromByteString) . bodyReaderSource $
          BE.responseBody res
        logging =
          if statusCode status `elem` [400, 500]
            then Log.warn
            else Log.debug
    logging $
      "BACKEND >>> " ++
      show (statusCode status) ++ " on " ++ msg ++ " " ++ show headers ++ "\n"
    resp $ responseSource status (modifyResponseHeaders headers) body

modifyRequestHeaders :: RequestHeaders -> RequestHeaders
modifyRequestHeaders = filter (\(n, _) -> n `notElem` ban)
  where
    ban =
      [ hConnection
      , hContentLength -- XXX This is set automtically before sending request to backend
      , hTransferEncoding -- XXX Likewise
      ]

modifyResponseHeaders :: ResponseHeaders -> ResponseHeaders
modifyResponseHeaders = filter (\(n, _) -> n `notElem` ban)
  where
    ban =
      [ hConnection
      -- XXX WAI docs say we MUST NOT add (keep) Content-Length, Content-Range, and Transfer-Encoding,
      -- XXX but we use streaming body, which may add Transfer-Encoding only.
      -- XXX Thus we keep Content-* headers.
      , hTransferEncoding
      ]

authenticationRequired ::
     ByteString -> HM.HashMap Text OAuth2Client -> W.Application
authenticationRequired key oa2 req resp = do
  Log.info $ "511 Unauthenticated: " ++ showReq req
  resp $
    W.responseLBS
      networkAuthenticationRequired511
      [(hContentType, "text/html; charset=utf-8")]
      page
  where
    path =
      if W.requestMethod req == methodGet
        then W.rawPathInfo req <> W.rawQueryString req
        else "/"
    state =
      State.encode key $
      "https://" <> fromJust (W.requestHeaderHost req) <> path
    authLink :: Text -> OAuth2Client -> ByteString -> ByteString
    authLink provider oa2c html =
      let u = oauth2AuthorizeURL oa2c state (redirectURL req provider)
          d = pack $ oauth2Description oa2c
      in [qc|{html}<p><a href="{u}">Authenticate with {d}</a></p>|]
    authHtml = HM.foldrWithKey authLink "" oa2
    page =
      fromStrict
        [qc|
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Authentication required</title>
  </head>
  <body style="text-align:center;">
  <h1>Authentication required</h1>
  {authHtml}
  </body>
</html>
|]

forbidden :: AuthCookie -> W.Application
forbidden ac req resp = do
  Log.info $ "403 Forbidden: " ++ show email ++ ": " ++ showReq req
  resp $
    W.responseLBS forbidden403 [(hContentType, "text/html; charset=utf-8")] page
  where
    email = getEmailUtf8 . acUser $ ac
    page =
      fromStrict
        [qc|
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Access Denied</title>
  </head>
  <body>
  <h1>Access Denied</h1>
    <p>You are currently logged in as <strong>{email}</strong></p>
    <p><a href="/.sproxy/logout">Logout</a></p>
  </body>
</html>
|]

userNotFound :: AuthUser -> W.Application
userNotFound au _ resp = do
  Log.info $ "404 User not found: " ++ show email
  resp $
    W.responseLBS notFound404 [(hContentType, "text/html; charset=utf-8")] page
  where
    email = getEmailUtf8 au
    page =
      fromStrict
        [qc|
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Access Denied</title>
  </head>
  <body>
  <h1>Access Denied</h1>
    <p>You are not allowed to login as <strong>{email}</strong></p>
    <p><a href="/">Main page</a></p>
  </body>
</html>
|]

logout :: ByteString -> ByteString -> Maybe ByteString -> W.Application
logout key cookieName cookieDomain req resp = do
  let host = fromJust $ W.requestHeaderHost req
  case extractCookie key Nothing cookieName req of
    Nothing ->
      resp $ W.responseLBS found302 [(hLocation, "https://" <> host)] ""
    Just _ -> do
      let cookie =
            WC.def
            { WC.setCookieName = cookieName
            , WC.setCookieHttpOnly = True
            , WC.setCookiePath = Just "/"
            , WC.setCookieSameSite = Just WC.sameSiteStrict
            , WC.setCookieSecure = True
            , WC.setCookieValue = "goodbye"
            , WC.setCookieDomain = cookieDomain
            , WC.setCookieExpires =
                Just . posixSecondsToUTCTime . realToFrac $ CTime 0
            }
      resp $
        W.responseLBS
          found302
          [ (hLocation, "https://" <> host)
          , ("Set-Cookie", toByteString $ WC.renderSetCookie cookie)
          ]
          ""

badRequest :: String -> W.Application
badRequest msg req resp = do
  Log.warn $ "400 Bad Request (" ++ msg ++ "): " ++ showReq req
  resp $ W.responseLBS badRequest400 [] "Bad Request"

notFound :: String -> W.Application
notFound msg req resp = do
  Log.warn $ "404 Not Found (" ++ msg ++ "): " ++ showReq req
  resp $ W.responseLBS notFound404 [] "Not Found"

logException :: W.Middleware
logException app req resp =
  catches (app req resp) [Handler badGateway, Handler internalError]
  where
    internalError :: SomeException -> IO W.ResponseReceived
    internalError = response internalServerError500
    badGateway :: BE.HttpException -> IO W.ResponseReceived
    badGateway = response badGateway502
    response :: Exception e => Status -> e -> IO W.ResponseReceived
    response st e = do
      Log.error $
        show (statusCode st) ++
        " " ++
        unpack (statusMessage st) ++
        ": " ++ displayException e ++ " on " ++ showReq req
      resp $
        W.responseLBS
          st
          [(hContentType, "text/plain")]
          (fromStrict $ statusMessage st)

get :: W.Middleware
get app req resp
  | W.requestMethod req == methodGet = app req resp
  | otherwise = do
    Log.warn $ "405 Method Not Allowed: " ++ showReq req
    resp $
      W.responseLBS methodNotAllowed405 [("Allow", "GET")] "Method Not Allowed"

post :: W.Middleware
post app req resp
  | W.requestMethod req == methodPost = app req resp
  | otherwise = do
    Log.warn $ "405 Method Not Allowed: " ++ showReq req
    resp $
      W.responseLBS methodNotAllowed405 [("Allow", "POST")] "Method Not Allowed"

redirectURL :: W.Request -> Text -> ByteString
redirectURL req provider =
  "https://" <> fromJust (W.requestHeaderHost req) <> "/.sproxy/oauth2/" <>
  encodeUtf8 provider

requestDomain :: W.Request -> Maybe ByteString
requestDomain req = do
  h <- W.requestHeaderHost req
  return . fst . BS.break (== _colon) $ h

-- XXX: make sure not to reveal the cookie, which can be valid (!)
showReq :: W.Request -> String
showReq req =
  unpack
    (W.requestMethod req <> " " <>
     fromMaybe "<no host>" (W.requestHeaderHost req) <>
     W.rawPathInfo req <>
     W.rawQueryString req <>
     " ") ++
  show (W.httpVersion req) ++
  " " ++
  show (fromMaybe "-" $ W.requestHeaderReferer req) ++
  " " ++
  show (fromMaybe "-" $ W.requestHeaderUserAgent req) ++
  " from " ++ show (W.remoteHost req)