{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards  #-}
{-# LANGUAGE RankNTypes  #-}

module Network.HTTP2.Client.FrameConnection (
      Http2FrameConnection(..)
    , newHttp2FrameConnection
    -- * Interact at the Frame level.
    , Http2ServerStream(..)
    , Http2FrameClientStream(..)
    , makeFrameClientStream
    , sendOne
    , sendBackToBack
    , next
    , closeConnection
    ) where

import           Control.DeepSeq (deepseq)
import           Control.Exception (bracket)
import           Control.Concurrent.MVar (newMVar, takeMVar, putMVar)
import           Control.Monad ((>=>), void)
import           Network.HTTP2 (FrameHeader(..), FrameFlags, FramePayload, HTTP2Error, encodeInfo, decodeFramePayload)
import qualified Network.HTTP2 as HTTP2
import           Network.Socket (HostName, PortNumber)
import qualified Network.TLS as TLS

import           Network.HTTP2.Client.RawConnection

data Http2FrameConnection = Http2FrameConnection {
    _makeFrameClientStream :: HTTP2.StreamId -> Http2FrameClientStream
  -- ^ Starts a new client stream.
  , _serverStream     :: Http2ServerStream
  -- ^ Receives frames from a server.
  , _closeConnection  :: IO ()
  -- ^ Function that will close the network connection.
  }

-- | Closes the Http2FrameConnection abruptly.
closeConnection :: Http2FrameConnection -> IO ()
closeConnection = _closeConnection

-- | Creates a client stream.
makeFrameClientStream :: Http2FrameConnection
                      -> HTTP2.StreamId
                      -> Http2FrameClientStream
makeFrameClientStream = _makeFrameClientStream

data Http2FrameClientStream = Http2FrameClientStream {
    _sendFrames :: IO [(FrameFlags -> FrameFlags, FramePayload)] -> IO ()
  -- ^ Sends a frame to the server.
  -- The first argument is a FrameFlags modifier (e.g., to sed the
  -- end-of-stream flag).
  , _getStreamId :: HTTP2.StreamId -- TODO: hide me
  }

-- | Sends a frame to the server.
sendOne :: Http2FrameClientStream -> (FrameFlags -> FrameFlags) -> FramePayload -> IO ()
sendOne client f payload = _sendFrames client (pure [(f, payload)])

-- | Sends multiple back-to-back frames to the server.
sendBackToBack :: Http2FrameClientStream -> [(FrameFlags -> FrameFlags, FramePayload)] -> IO ()
sendBackToBack client payloads = _sendFrames client (pure payloads)

data Http2ServerStream = Http2ServerStream {
    _nextHeaderAndFrame :: IO (FrameHeader, Either HTTP2Error FramePayload)
  }

-- | Waits for the next frame from the server.
next :: Http2FrameConnection -> IO (FrameHeader, Either HTTP2Error FramePayload)
next = _nextHeaderAndFrame . _serverStream

-- | Adds framing around a 'RawHttp2Connection'.
frameHttp2RawConnection
  :: RawHttp2Connection
  -> IO Http2FrameConnection
frameHttp2RawConnection http2conn = do
    -- Prepare a local mutex, this mutex should never escape the
    -- function's scope. Else it might lead to bugs (e.g.,
    -- https://ro-che.info/articles/2014-07-30-bracket ) 
    writerMutex <- newMVar () 

    let writeProtect io =
            bracket (takeMVar writerMutex) (putMVar writerMutex) (const io)

    -- Define handlers.
    let makeClientStream streamID = 
            let putFrame modifyFF frame =
                    let info = encodeInfo modifyFF streamID
                    in HTTP2.encodeFrame info frame
                putFrames f = writeProtect . void $ do
                    xs <- f
                    let ys = fmap (uncurry putFrame) xs
                    -- Force evaluation of frames serialization whilst
                    -- write-protected to avoid out-of-order errrors.
                    deepseq ys (_sendRaw http2conn ys)
             in Http2FrameClientStream putFrames streamID

        nextServerFrameChunk = Http2ServerStream $ do
            (fTy, fh@FrameHeader{..}) <- HTTP2.decodeFrameHeader <$> _nextRaw http2conn 9
            let decoder = decodeFramePayload fTy
            -- TODO: consider splitting the iteration here to give a chance to
            -- _not_ decode the frame, or consider lazyness enough.
            let getNextFrame = decoder fh <$> _nextRaw http2conn payloadLength
            nf <- getNextFrame
            return (fh, nf)

        gtfo = _close http2conn

    return $ Http2FrameConnection makeClientStream nextServerFrameChunk gtfo

-- | Creates a new 'Http2FrameConnection' to a given host for a frame-to-frame communication.
newHttp2FrameConnection :: HostName
                        -> PortNumber
                        -> Maybe TLS.ClientParams
                        -> IO Http2FrameConnection
newHttp2FrameConnection host port params = do
    frameHttp2RawConnection =<< newRawHttp2Connection host port params