{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE DeriveGeneric #-}

-- | Interprocess communication
--
-- Prior art:
-- - <https://github.com/jb55/httpipe>
-- - <https://patchbay.pub>
-- - <https://github.com/hargettp/courier>
-- - sorta: <https://ngrok.com/> and <https://localtunnel.github.io/www/>
--
-- : exe que-server
--
-- : dep async
-- : dep envy
-- : dep protolude
-- : dep scotty
-- : dep stm
-- : dep unagi-chan
-- : dep unordered-containers
module Que.Server
  ( main
  )
where

import           Alpha                   hiding ( Text
                                                , get
                                                , gets
                                                , modify
                                                , poll
                                                )
import qualified Control.Concurrent.Go         as Go
import qualified Control.Concurrent.STM        as STM
import qualified Control.Exception             as Exception
import           Control.Monad.Reader           ( MonadTrans )
import qualified Data.ByteString.Builder.Extra as Builder
import qualified Data.ByteString.Lazy          as BSL
import           Data.HashMap.Lazy              ( HashMap )
import qualified Data.HashMap.Lazy             as HashMap
import qualified Data.Text.Encoding            as Encoding
import           Data.Text.Lazy                 ( Text
                                                , fromStrict
                                                )
import qualified Data.Text.Lazy.IO             as Text
import qualified Network.HTTP.Types.Status     as Http
import qualified Network.Wai                   as Wai
import qualified Network.Wai.Handler.Warp      as Warp
import           Network.Wai.Middleware.RequestLogger
                                                ( logStdout )
import qualified System.Envy                   as Envy
import qualified System.Exit                   as Exit
import qualified Web.Scotty.Trans              as Scotty

main :: IO ()
main = Exception.bracket startup shutdown <| uncurry Warp.run
 where
  startup = Envy.decodeEnv >>= \case
    Left  e -> Exit.die e
    Right c -> do
      sync <- STM.newTVarIO initialAppState
      let runActionToIO m = runReaderT (runApp m) sync
      waiapp <- Scotty.scottyAppT runActionToIO routes
      putText <| "port:" <> (show <| quePort c)
      return (quePort c, waiapp)
  shutdown :: a -> IO a
  shutdown = pure . identity

newtype App a = App
  { runApp :: ReaderT (STM.TVar AppState) IO a
  }
  deriving (Applicative, Functor, Monad, MonadIO, MonadReader
    (STM.TVar AppState))

data AppState = AppState
  { ques :: HashMap Namespace Quebase
  }

initialAppState :: AppState
initialAppState = AppState { ques = mempty }

data Config = Config
  { quePort :: Warp.Port -- ^ QUE_PORT
  } deriving (Generic, Show)

instance Envy.DefConfig Config where
  defConfig = Config 3000

instance Envy.FromEnv Config

routes :: Scotty.ScottyT Text App ()
routes = do
  Scotty.middleware logStdout

  let quepath   = "^\\/([[:alnum:]_]+)\\/([[:alnum:]._/]*)$"
  let namespace = "^\\/([[:alnum:]_]+)\\/?$" -- matches '/ns' and '/ns/' but not '/ns/path'

  -- | GET /index.html
  Scotty.get (Scotty.literal "/index.html") <| Scotty.redirect "/_/index"
  Scotty.get (Scotty.literal "/") <| Scotty.redirect "/_/index"

  -- | GET /_/dash
  Scotty.get (Scotty.literal "/_/dash") <| do
    authkey  <- fromMaybe "" </ Scotty.header "Authorization"
    adminkey <- liftIO <| lchomp </ Text.readFile "/run/keys/que-admin"
    if authkey == adminkey
      then do
        d <- app <| gets ques
        Scotty.json d
      else do
        Scotty.status Http.methodNotAllowed405
        Scotty.text "not allowed"


  -- | Namespace management
  Scotty.matchAny (Scotty.regex namespace) <| do
    Scotty.status Http.notImplemented501
    Scotty.text "namespace management coming soon"

  -- | GET que
  --
  -- Receive a value from a que. Blocks until a value is received,
  -- then returns. If 'poll=true', then stream data from the Que to the
  -- client.
  Scotty.get (Scotty.regex quepath) <| do
    (ns, qp) <- extract
    app . modify <| upsertNamespace ns
    q    <- app <| que ns qp
    poll <- Scotty.param "poll" !: (pure . const False)
    guardNs ns ["pub", "_"]
    case poll of
      True -> Scotty.stream $ streamQue q
      _    -> do
        r <- liftIO <| Go.read q
        Scotty.html <| fromStrict <| Encoding.decodeUtf8 r

  -- | POST que
  --
  -- Put a value on a que. Returns immediately.
  Scotty.post (Scotty.regex quepath) <| do
    authkey  <- fromMaybe "" </ Scotty.header "Authorization"
    adminkey <- liftIO <| lchomp </ Text.readFile "/run/keys/que-admin"
    (ns, qp) <- extract
    -- Only allow my IP or localhost to publish to '_' namespace
    when ("_" == ns && authkey /= adminkey)
      <| Scotty.status Http.methodNotAllowed405
      >> Scotty.text "not allowed: _ is a reserved namespace"
      >> Scotty.finish
    guardNs ns ["pub", "_"]
    -- passed all auth checks
    app . modify <| upsertNamespace ns
    q     <- app <| que ns qp
    qdata <- Scotty.body
    _     <- liftIO <| Go.write q <| BSL.toStrict qdata
    return ()

-- | Given `guardNs ns whitelist`, if `ns` is not in the `whitelist`
-- list, return a 405 error.
guardNs :: Text -> [Text] -> Scotty.ActionT Text App ()
guardNs ns whitelist = when (not <| ns `elem` whitelist) <| do
  Scotty.status Http.methodNotAllowed405
  Scotty.text
    <| "not allowed: use 'pub' namespace or signup to protect '"
    <> ns
    <> "' at https://que.run"
  Scotty.finish

-- | recover from a scotty-thrown exception.
(!:)
  :: Scotty.ActionT Text App a -- ^ action that might throw
  -> (Text -> Scotty.ActionT Text App a) -- ^ a function providing a default response instead
  -> Scotty.ActionT Text App a
(!:) = Scotty.rescue

-- | Forever write the data from 'Que' to 'Wai.StreamingBody'.
streamQue :: Que -> Wai.StreamingBody
streamQue q write _ = Go.mult q >>= loop
 where
  loop c =
    Go.tap c
      >>= (write . Builder.byteStringInsert)
      >>  (write <| Builder.byteStringInsert "\n")
      >>  loop c

-- | Gets the thing from the Hashmap. Call's 'error' if key doesn't exist.
grab :: (Eq k, Hashable k) => k -> HashMap k v -> v
grab = flip (HashMap.!)

-- | Inserts the namespace in 'AppState' if it doesn't exist.
upsertNamespace :: Namespace -> AppState -> AppState
upsertNamespace ns as = if HashMap.member ns (ques as)
  then as
  else as { ques = HashMap.insert ns mempty (ques as) }

-- | Inserts the que at the proper 'Namespace' and 'Quepath'.
insertQue :: Namespace -> Quepath -> Que -> AppState -> AppState
insertQue ns qp q as = as { ques = newQues }
 where
  newQues  = HashMap.insert ns newQbase (ques as)
  newQbase = HashMap.insert qp q <| grab ns <| ques as

extract :: Scotty.ActionT Text App (Namespace, Quepath)
extract = do
  ns   <- Scotty.param "1"
  path <- Scotty.param "2"
  return (ns, path)

-- | A synonym for 'lift' in order to be explicit about when we are
-- operating at the 'App' layer.
app :: MonadTrans t => App a -> t App a
app = lift

-- | Get something from the app state
gets :: (AppState -> b) -> App b
gets f = ask >>= liftIO . STM.readTVarIO >>= return . f

-- | Apply a function to the app state
modify :: (AppState -> AppState) -> App ()
modify f = ask >>= liftIO . atomically . flip STM.modifyTVar' f

type Namespace = Text -- ^ housing for a set of que paths
type Que = Go.Channel Message -- ^ a que is just a channel of bytes
type Quepath = Text -- ^ any path can serve as an identifier for a que
type Message = ByteString -- ^ any opaque data
type Quebase = HashMap Quepath Que -- ^ a collection of ques

-- | Lookup or create a que
que :: Namespace -> Quepath -> App Que
que ns qp = do
  _ques <- gets ques
  let qbase     = grab ns _ques
      queExists = HashMap.member qp qbase
  if queExists
    then return <| grab qp qbase
    else do
      c <- liftIO <| Go.chan 1
      modify (insertQue ns qp c)
      gets ques /> grab ns /> grab qp