-- | An example of a custom authentication framework that checks a Cookie for a
-- value.

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ScopedTypeVariables #-}

import Data.Aeson
import Data.ByteString (ByteString)
import Data.ByteString.Builder.Internal (byteStringCopy)
import Data.Monoid ((<>))
import Data.Text (Text)
import GHC.Generics
import Network.HTTP.Types
import Network.Wai
import Network.Wai.Handler.Warp
import Servant
import Servant.API.Authentication
import Servant.Server.Internal
import Servant.Server.Internal.Authentication (strictProtect, AuthHandlers(AuthHandlers))

-- | Data we will use to test for authentication
data CookieAuth = CookieAuth { cookie :: ByteString }

-- | A 'User' datatype we get once the authentication data is tested.
type User = ByteString

-- | We will look up authentication data in the database and extract a User.
type DBLookup = CookieAuth -> IO (Maybe User)

-- | Method that tests for authentication and extracts a User type.
isGoodCookie :: DBLookup
isGoodCookie (CookieAuth cookie) = if cookie == "good cookie" then return (Just "one user") else return Nothing

-- | Response handlers: what do we do when authentication doesn't work.
cookieAuthHandlers :: AuthHandlers CookieAuth
cookieAuthHandlers = AuthHandlers missingAuth notAuthenticated
  where
    missingAuth :: IO Response
    missingAuth = return $ (responseBuilder status401 [] "Missing Cookie header.")

    notAuthenticated :: CookieAuth -> IO Response
    notAuthenticated (CookieAuth cookie) = return $
        responseBuilder status401 [] ("Invalid cookie: " <> byteStringCopy cookie)

-- | 'AuthData' is a typeclass that provides a method to extract authentication
-- data from a 'Request'
instance AuthData CookieAuth where
    authData req = fmap CookieAuth (lookup "Cookie" (requestHeaders req))

-- | Some data we will return from our API that is protected
newtype PrivateData = PrivateData { ssshhh :: Text }
  deriving (Eq, Show, Generic)

instance ToJSON PrivateData

-- | Some data we will return from our API that is not protected
newtype PublicData = PublicData { somedata :: Text }
  deriving (Eq, Show, Generic)

instance ToJSON PublicData

-- | Private API (will require authentication) as a type
type PrivateAPI = Get '[JSON] [PrivateData]

-- | Public API (non-authenticated) as a type
type PublicAPI = Get '[JSON] [PublicData]

-- | Our full API as a type with authentication
type API = AuthProtect CookieAuth User 'Strict :> "private" :>  PrivateAPI
      :<|> PublicAPI

api :: Proxy API
api = Proxy

server :: Server API
server = strictProtect isGoodCookie cookieAuthHandlers (const (return prvdata))
    :<|> return pubdata

  where prvdata = [PrivateData "this is a secret"]
        pubdata = [PublicData "this is a public piece of data"]

main :: IO ()
main = run 8080 (serve api server)

{- Sample session:
$ curl http://localhost:8080/
[{"somedata":"this is a public piece of data"}]
$ curl http://localhost:8080/private
Missing auth header.
$ curl -H "Cookie: good password" http://localhost:8080/private
[{"ssshhh":"this is a secret"}]
$ curl -H "Cookie: bad password" http://localhost:8080/private
Invalid cookie.
-}