{-# LANGUAGE AllowAmbiguousTypes   #-}
{-# LANGUAGE CPP                   #-}
{-# LANGUAGE DataKinds             #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE InstanceSigs          #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedStrings     #-}
{-# LANGUAGE ScopedTypeVariables   #-}
{-# LANGUAGE TypeApplications      #-}
{-# LANGUAGE TypeFamilies          #-}
{-# LANGUAGE TypeOperators         #-}
{-# LANGUAGE UndecidableInstances  #-}


-- | Since the single page application URIs are specified with Servant, we can automate much
-- of the process of serving the application with server-side rendering. This module provides
-- the basic infrastructure for serving rendered HTML using the same code that would be used
-- to render the same route on the client-side, ensuring a consistent rendering, whether a
-- URI is accessed via a client-side popstate event or via the initial page load.


module Shpadoinkle.Router.Server where


#ifndef ghcjs_HOST_OS


import           Data.ByteString.Lazy           as BS (ByteString, fromStrict,
                                                       length)
import qualified Data.ByteString.Lazy           as BSL
import           Data.Text.Encoding             (encodeUtf8)
import           GHC.TypeLits                   (Symbol)
import           Network.HTTP.Types
import           Network.Wai                    (Application, responseLBS)
import           Network.Wai.Application.Static (StaticSettings (ssLookupFile, ssMaxAge),
                                                 defaultWebAppSettings,
                                                 staticApp)
import           Servant.API
import           Servant.Server                 (HasServer (ServerT), Server)
import           Servant.Server.StaticFiles     (serveDirectoryWith)
import           WaiAppStatic.Types             (File (..),
                                                 LookupResult (LRFile, LRNotFound),
                                                 MaxAge (MaxAgeSeconds), Piece,
                                                 toPieces)

import           Shpadoinkle                    (Html)
import           Shpadoinkle.Backend.Static     (renderStatic)
import           Shpadoinkle.Router             (HasRouter (..), View)


-- | Helper to serve a 'ByteString' as a file from the web application interface.
toFile :: Piece -> ByteString -> File
toFile p bs = File
  { fileGetSize     = fromIntegral $ BS.length bs
  , fileToResponse  = \status headers -> responseLBS status headers bs
  , fileName        = p
  , fileGetHash     = pure Nothing
  , fileGetModified = Nothing
  }


-- | Serve index.html generated from a Shpadoinkle view using the static backend, otherwise serve out of a directory.
defaultSPAServerSettings
  :: FilePath
  -- ^ Directory to try files
  -> IO (Html m a)
  -- ^ Get the index.html page
  -> StaticSettings
defaultSPAServerSettings root mhtml = settings { ssLookupFile = orIndex, ssMaxAge = MaxAgeSeconds 0 }
  where

  settings   = defaultWebAppSettings root

  orIndex ps = do
    let file ps' = toFile ps' . BS.fromStrict . encodeUtf8 . renderStatic
    res <- ssLookupFile settings ps
    html <- mhtml
    return $ case (res, toPieces ["index.html"]) of
      (LRNotFound, Just [ps'])                                  -> LRFile $ file ps' html
      (_,          Just [ps']) | [ps'] == ps || Prelude.null ps -> LRFile $ file ps' html
      _                                                         -> res


-- | Serve the UI by generating a Servant Server from the SPA URIs
class ServeRouter layout route m a where
  serveUI
    :: FilePath
    -- ^ Where should we look for static assets?
    -> (route -> IO (Html m a))
    -- ^ How shall we get the page based on the requested route?
    -> layout :>> route
    -- ^ What is the relationship between URIs and routes?
    -> Server layout


instance (ServeRouter x r m a, ServeRouter y r m a)
  => ServeRouter (x :<|> y) r m a where

  serveUI :: FilePath -> (r -> IO (Html m a)) -> (x :<|> y) :>> r -> Server (x :<|> y)
  serveUI root view (x :<|> y) = serveUI @x root view x :<|> serveUI @y root view y
  {-# INLINABLE serveUI #-}

instance ServeRouter sub r m a
  => ServeRouter (Capture sym x :> sub) r m a where

  serveUI :: FilePath -> (r -> IO (Html m a)) -> (x -> sub :>> r) -> Server (Capture sym x :> sub)
  serveUI root view = (serveUI @sub root view .)
  {-# INLINABLE serveUI #-}

instance ServeRouter sub r m a
  => ServeRouter (QueryParam sym x :> sub) r m a where

  serveUI :: FilePath -> (r -> IO (Html m a)) -> (Maybe x -> sub :>> r) -> Server (QueryParam sym x :> sub)
  serveUI root view = (serveUI @sub root view .)
  {-# INLINABLE serveUI #-}

instance ServeRouter sub r m a
  => ServeRouter (QueryParams sym x :> sub) r m a where

  serveUI :: FilePath -> (r -> IO (Html m a)) -> ([x] -> sub :>> r) -> Server (QueryParams sym x :> sub)
  serveUI root view = (serveUI @sub root view .)
  {-# INLINABLE serveUI #-}

instance ServeRouter sub r m a
  => ServeRouter (QueryFlag sym :> sub) r m a where

  serveUI :: FilePath -> (r -> IO (Html m a)) -> (Bool -> sub :>> r) -> Server (QueryFlag sym :> sub)
  serveUI root view = (serveUI @sub root view .)
  {-# INLINABLE serveUI #-}

instance ServeRouter sub r m a
  => ServeRouter ((path :: Symbol) :> sub) r m a where

  serveUI :: FilePath -> (r -> IO (Html m a)) -> (path :> sub) :>> r -> Server (path :> sub)
  serveUI = serveUI @sub
  {-# INLINABLE serveUI #-}

instance ServeRouter Raw r m a where
  serveUI :: FilePath -> (r -> IO (Html m a)) -> Raw :>> r -> Server Raw
  serveUI root view = serveDirectoryWith . defaultSPAServerSettings root . view
  {-# INLINABLE serveUI #-}

instance ServeRouter (View n b) r m a where
  serveUI :: FilePath -> (r -> IO (Html m a)) -> View n b :>> r -> Server (View n b)
  serveUI root view = serveDirectoryWithSpa . defaultSPAServerSettings root . view
  {-# INLINABLE serveUI #-}


serveDirectoryWithSpa :: Applicative n => StaticSettings -> ServerT (View m a) n
serveDirectoryWithSpa = pure . staticApp


serveHtml :: Html m a -> Application
serveHtml html _ respond
  = respond . responseLBS status200 [(hContentType, "text/html")]
  . BSL.fromStrict . encodeUtf8 $ renderStatic html
#endif