{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ScopedTypeVariables #-}

{- | Note: The functions that are designated as being intended for stream
sockets convert a reception length of zero to an non-standard @EOI@ error
code. Datagram reception functions do not do this.
-}
module Network.Unexceptional.MutableBytes
  ( -- * Stream Sockets
    receive
  , receiveInterruptible
  , receiveExactly
  , receiveExactlyInterruptible

    -- * Datagram Sockets
  , receiveFromInterruptible
  ) where

import Control.Applicative ((<|>))
import Control.Concurrent.STM (STM, TVar)
import Control.Exception (throwIO)
import Control.Monad ((<=<))
import Data.Bytes.Types (MutableBytes (MutableBytes))
import Data.Functor (($>))
import Data.Primitive (MutableByteArray)
import Foreign.C.Error (Errno)
import Foreign.C.Error.Pattern
  ( pattern EAGAIN
  , pattern EEOI
  , pattern EWOULDBLOCK
  )
import Foreign.C.Types (CSize)
import Foreign.Ptr (castPtr)
import GHC.Conc (threadWaitRead, threadWaitReadSTM)
import GHC.Exts (Ptr, RealWorld)
import Network.Socket (SockAddr, Socket)
import Network.Socket.Address (peekSocketAddress)
import System.Posix.Types (Fd (Fd))

import qualified Control.Concurrent.STM as STM
import qualified Data.Bytes.Types
import qualified Data.Primitive as PM
import qualified Linux.Socket as X
import qualified Network.Socket as S
import qualified Network.Unexceptional.Types as Types
import qualified Posix.Socket as X

{- | Receive bytes from a socket. Receives at most N bytes, where N
is the size of the buffer. Returns the number of bytes that were
actually received.
-}
receive ::
  Socket ->
  -- | Slice of a buffer
  MutableBytes RealWorld ->
  IO (Either Errno Int)
receive s MutableBytes {array, offset, length = len} =
  if len > 0
    then S.withFdSocket s $ \fd ->
      -- We attempt the first receive without testing if the socket is
      -- ready for reads.
      receiveLoop (Fd fd) array offset len
    else throwIO Types.NonpositiveReceptionSize

{- | Receive bytes from a socket. Receives at most N bytes, where N
is the size of the buffer. Returns the number of bytes that were
actually received.
-}
receiveFromInterruptible ::
  TVar Bool ->
  Socket ->
  -- | Slice of a buffer
  MutableBytes RealWorld ->
  IO (Either Errno (Int, SockAddr))
receiveFromInterruptible !interrupt s MutableBytes {array, offset, length = len} =
  if len > 0
    then S.withFdSocket s $ \fd -> do
      -- We attempt the first receive without testing if the socket is
      -- ready for reads.
      receiveFromInterruptibleLoop interrupt (Fd fd) array offset len
    else throwIO Types.NonpositiveReceptionSize

receiveFromInterruptibleLoop ::
  TVar Bool ->
  Fd ->
  MutableByteArray RealWorld ->
  Int ->
  Int ->
  IO (Either Errno (Int, SockAddr))
receiveFromInterruptibleLoop !intr !fd !dst !doff !dlen =
  X.uninterruptibleReceiveFromMutableByteArray fd dst doff (fromIntegral dlen :: CSize) mempty 128 >>= \case
    Left e ->
      if e == EAGAIN || e == EWOULDBLOCK
        then
          waitUntilReadable intr fd >>= \case
            Ready -> receiveFromInterruptibleLoop intr fd dst doff dlen
            Interrupted -> pure (Left EAGAIN)
        else pure (Left e)
    Right (sockAddrSz, X.SocketAddress sockAddr, recvSzC) -> do
      let sockAddrSzI = fromIntegral sockAddrSz :: Int
      pinned <- PM.newPinnedByteArray sockAddrSzI
      PM.copyByteArray pinned 0 sockAddr 0 sockAddrSzI
      pinned' <- PM.unsafeFreezeByteArray pinned
      sockAddrNetwork <- PM.withByteArrayContents pinned' $ \ptr -> do
        peekSocketAddress (castPtr ptr :: Ptr sa)
      let recvSz = fromIntegral recvSzC :: Int
       in case compare recvSz dlen of
            GT -> throwIO Types.ReceivedTooManyBytes
            _ -> pure (Right (recvSz, sockAddrNetwork))

receiveInterruptible ::
  -- | Interrupt
  TVar Bool ->
  Socket ->
  -- | Slice of a buffer
  MutableBytes RealWorld ->
  IO (Either Errno Int)
receiveInterruptible !interrupt s MutableBytes {array, offset, length = len} =
  if len > 0
    then S.withFdSocket s $ \fd ->
      -- We attempt the first receive without testing if the socket is
      -- ready for reads.
      receiveInterruptibleLoop interrupt (Fd fd) array offset len
    else throwIO Types.NonpositiveReceptionSize

-- Does not wait for file descriptor to be ready. Only performs
-- a single successful recv syscall
receiveLoop :: Fd -> MutableByteArray RealWorld -> Int -> Int -> IO (Either Errno Int)
receiveLoop !fd !arr !off !len =
  X.uninterruptibleReceiveMutableByteArray fd arr off (fromIntegral len) X.dontWait >>= \case
    Left e ->
      if e == EAGAIN || e == EWOULDBLOCK
        then do
          threadWaitRead fd
          receiveLoop fd arr off len
        else pure (Left e)
    Right recvSzC ->
      let recvSz = fromIntegral recvSzC :: Int
       in case recvSz of
            0 -> pure (Left EEOI)
            _ -> case compare recvSz len of
              GT -> throwIO Types.ReceivedTooManyBytes
              _ -> pure (Right recvSz)

-- Does not wait for file descriptor to be ready. Only performs
-- a single successful recv syscall
receiveInterruptibleLoop :: TVar Bool -> Fd -> MutableByteArray RealWorld -> Int -> Int -> IO (Either Errno Int)
receiveInterruptibleLoop !interrupt !fd !arr !off !len =
  X.uninterruptibleReceiveMutableByteArray fd arr off (fromIntegral len) X.dontWait >>= \case
    Left e ->
      if e == EAGAIN || e == EWOULDBLOCK
        then
          waitUntilReadable interrupt fd >>= \case
            Ready -> receiveInterruptibleLoop interrupt fd arr off len
            Interrupted -> pure (Left EAGAIN)
        else pure (Left e)
    Right recvSzC ->
      let recvSz = fromIntegral recvSzC :: Int
       in case recvSz of
            0 -> pure (Left EEOI)
            _ -> case compare recvSz len of
              GT -> throwIO Types.ReceivedTooManyBytes
              _ -> pure (Right recvSz)

checkFinished :: TVar Bool -> STM ()
checkFinished = STM.check <=< STM.readTVar

data Outcome = Ready | Interrupted

waitUntilReadable :: TVar Bool -> Fd -> IO Outcome
waitUntilReadable !interrupt !fd = do
  (isReadyAction, deregister) <- threadWaitReadSTM fd
  outcome <- STM.atomically $ (isReadyAction $> Ready) <|> (checkFinished interrupt $> Interrupted)
  deregister
  pure outcome

-- | Blocks until an exact number of bytes has been received.
receiveExactly ::
  Socket ->
  -- | Length is the exact number of bytes to receive,
  -- must be greater than zero.
  MutableBytes RealWorld ->
  IO (Either Errno ())
receiveExactly s (MutableBytes dst off0 n) =
  if n > 0
    then do
      let loop !ix !remaining = case remaining of
            0 -> pure (Right ())
            _ ->
              receive s (MutableBytes dst ix remaining) >>= \case
                Left e -> pure (Left e)
                Right k -> loop (ix + k) (remaining - k)
      loop off0 n
    else throwIO Types.NonpositiveReceptionSize

receiveExactlyInterruptible ::
  TVar Bool ->
  Socket ->
  -- | Length is the exact number of bytes to receive,
  -- must be greater than zero.
  MutableBytes RealWorld ->
  IO (Either Errno ())
receiveExactlyInterruptible !intr !s (MutableBytes dst off0 n) =
  if n > 0
    then do
      let loop !ix !remaining = case remaining of
            0 -> pure (Right ())
            _ ->
              receiveInterruptible intr s (MutableBytes dst ix remaining) >>= \case
                Left e -> pure (Left e)
                Right k -> loop (ix + k) (remaining - k)
      loop off0 n
    else throwIO Types.NonpositiveReceptionSize