{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ViewPatterns #-}
module Network.HTTP.Client.Connection
    ( connectionReadLine
    , connectionReadLineWith
    , connectionDropTillBlankLine
    , dummyConnection
    , openSocketConnection
    , openSocketConnectionSize
    , makeConnection
    , socketConnection
    , withSocket
    , strippedHostName
    ) where

import Data.ByteString (ByteString, empty)
import Data.IORef
import Control.Monad
import Control.Concurrent
import Control.Concurrent.Async
import Network.HTTP.Client.Types
import Network.Socket (Socket, HostAddress)
import qualified Network.Socket as NS
import Network.Socket.ByteString (sendAll, recv)
import qualified Control.Exception as E
import qualified Data.ByteString as S
import Data.Foldable (for_)
import Data.Function (fix)
import Data.Maybe (listToMaybe)
import Data.Word (Word8)


connectionReadLine :: Connection -> IO ByteString
connectionReadLine conn = do
    bs <- connectionRead conn
    when (S.null bs) $ throwHttp IncompleteHeaders
    connectionReadLineWith conn bs

-- | Keep dropping input until a blank line is found.
connectionDropTillBlankLine :: Connection -> IO ()
connectionDropTillBlankLine conn = fix $ \loop -> do
    bs <- connectionReadLine conn
    unless (S.null bs) loop

connectionReadLineWith :: Connection -> ByteString -> IO ByteString
connectionReadLineWith conn bs0 =
    go bs0 id 0
  where
    go bs front total =
        case S.break (== charLF) bs of
            (_, "") -> do
                let total' = total + S.length bs
                when (total' > 4096) $ throwHttp OverlongHeaders
                bs' <- connectionRead conn
                when (S.null bs') $ throwHttp IncompleteHeaders
                go bs' (front . (bs:)) total'
            (x, S.drop 1 -> y) -> do
                unless (S.null y) $! connectionUnread conn y
                return $! killCR $! S.concat $! front [x]

charLF, charCR :: Word8
charLF = 10
charCR = 13

killCR :: ByteString -> ByteString
killCR bs
    | S.null bs = bs
    | S.last bs == charCR = S.init bs
    | otherwise = bs

-- | For testing
dummyConnection :: [ByteString] -- ^ input
                -> IO (Connection, IO [ByteString], IO [ByteString]) -- ^ conn, output, input
dummyConnection input0 = do
    iinput <- newIORef input0
    ioutput <- newIORef []
    return (Connection
        { connectionRead = atomicModifyIORef iinput $ \input ->
            case input of
                [] -> ([], empty)
                x:xs -> (xs, x)
        , connectionUnread = \x -> atomicModifyIORef iinput $ \input -> (x:input, ())
        , connectionWrite = \x -> atomicModifyIORef ioutput $ \output -> (output ++ [x], ())
        , connectionClose = return ()
        }, atomicModifyIORef ioutput $ \output -> ([], output), readIORef iinput)

-- | Create a new 'Connection' from a read, write, and close function.
--
-- @since 0.5.3
makeConnection :: IO ByteString -- ^ read
               -> (ByteString -> IO ()) -- ^ write
               -> IO () -- ^ close
               -> IO Connection
makeConnection r w c = do
    istack <- newIORef []

    -- it is necessary to make sure we never read from or write to
    -- already closed connection.
    closedVar <- newIORef False

    let close = do
          closed <- atomicModifyIORef closedVar (\closed -> (True, closed))
          unless closed $
            c

    _ <- mkWeakIORef istack close
    return $! Connection
        { connectionRead = do
            closed <- readIORef closedVar
            when closed $ throwHttp ConnectionClosed
            join $ atomicModifyIORef istack $ \stack ->
              case stack of
                  x:xs -> (xs, return x)
                  [] -> ([], r)

        , connectionUnread = \x -> do
            closed <- readIORef closedVar
            when closed $ throwHttp ConnectionClosed
            atomicModifyIORef istack $ \stack -> (x:stack, ())

        , connectionWrite = \x -> do
            closed <- readIORef closedVar
            when closed $ throwHttp ConnectionClosed
            w x

        , connectionClose = close
        }

-- | Create a new 'Connection' from a 'Socket'.
--
-- @since 0.5.3
socketConnection :: Socket
                 -> Int -- ^ chunk size
                 -> IO Connection
socketConnection socket chunksize = makeConnection
    (recv socket chunksize)
    (sendAll socket)
    (NS.close socket)

openSocketConnection :: (Socket -> IO ())
                     -> Maybe HostAddress
                     -> String -- ^ host
                     -> Int -- ^ port
                     -> IO Connection
openSocketConnection f = openSocketConnectionSize f 8192

openSocketConnectionSize :: (Socket -> IO ())
                         -> Int -- ^ chunk size
                         -> Maybe HostAddress
                         -> String -- ^ host
                         -> Int -- ^ port
                         -> IO Connection
openSocketConnectionSize tweakSocket chunksize hostAddress' host' port' =
    withSocket tweakSocket hostAddress' host' port' $ \ sock ->
        socketConnection sock chunksize

-- | strippedHostName takes a URI host name, as extracted
-- by 'Network.URI.regName', and strips square brackets
-- around IPv6 addresses.
--
-- The result is suitable for passing to services such as
-- name resolution ('Network.Socket.getAddr').
--
-- @since
strippedHostName :: String -> String
strippedHostName hostName =
    case hostName of
        '[':'v':_ -> hostName -- IPvFuture, no obvious way to deal with this
        '[':rest ->
            case break (== ']') rest of
                (ipv6, "]") -> ipv6
                _ -> hostName -- invalid host name
        _ -> hostName

withSocket :: (Socket -> IO ())
           -> Maybe HostAddress
           -> String -- ^ host
           -> Int -- ^ port
           -> (Socket -> IO a)
           -> IO a
withSocket tweakSocket hostAddress' host' port' f = do
    let hints = NS.defaultHints { NS.addrSocketType = NS.Stream }
    addrs <- case hostAddress' of
        Nothing ->
            NS.getAddrInfo (Just hints) (Just $ strippedHostName host') (Just $ show port')
        Just ha ->
            return
                [NS.AddrInfo
                 { NS.addrFlags = []
                 , NS.addrFamily = NS.AF_INET
                 , NS.addrSocketType = NS.Stream
                 , NS.addrProtocol = 6 -- tcp
                 , NS.addrAddress = NS.SockAddrInet (toEnum port') ha
                 , NS.addrCanonName = Nothing
                 }]

    E.bracketOnError (firstSuccessful addrs $ openSocket tweakSocket) NS.close f

openSocket tweakSocket addr =
    E.bracketOnError
        (NS.socket (NS.addrFamily addr) (NS.addrSocketType addr)
                   (NS.addrProtocol addr))
        NS.close
        (\sock -> do
            NS.setSocketOption sock NS.NoDelay 1
            tweakSocket sock
            NS.connect sock (NS.addrAddress addr)
            return sock)

-- Pick up an IP using an approximation of the happy-eyeballs algorithm:
-- https://datatracker.ietf.org/doc/html/rfc8305
--
firstSuccessful :: [NS.AddrInfo] -> (NS.AddrInfo -> IO a) -> IO a
firstSuccessful []        _  = error "getAddrInfo returned empty list"
firstSuccessful addresses cb = do
    result <- newEmptyMVar
    either E.throwIO pure =<<
        withAsync (tryAddresses result)
            (\_ -> takeMVar result)
  where
    -- https://datatracker.ietf.org/doc/html/rfc8305#section-5
    connectionAttemptDelay = 250 * 1000

    tryAddresses result = do
        z <- forConcurrently (zip addresses [0..]) $ \(addr, n) -> do
            when (n > 0) $ threadDelay $ n * connectionAttemptDelay
            tryAddress addr

        case listToMaybe (reverse z) of
            Just e@(Left _) -> tryPutMVar result e
            _               -> error $ "tryAddresses invariant violated: " ++ show addresses
      where
        tryAddress addr = do
            r :: Either E.IOException a <- E.try $! cb addr
            for_ r $ \_ -> tryPutMVar result r
            pure r