{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE OverloadedStrings #-}

-- | Mock Memcached server - just enough for testing client.
module MockServer (
        MockResponse(..), mockMCServer, withMCServer
    ) where

import qualified Database.Memcache.Client as M
import           Database.Memcache.Socket
import           Database.Memcache.Types

import           Blaze.ByteString.Builder
#if __GLASGOW_HASKELL__ < 710
import           Control.Applicative
#endif
import           Control.Concurrent
import           Control.Exception (bracket, handle, throwIO, SomeException)
import           Control.Monad
import           Data.Binary.Get
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as BC
import qualified Data.ByteString.Lazy as L
import           Data.IORef
import           Data.Monoid
import           Data.Word
import qualified Network.Socket as N hiding (recv)
import qualified Network.Socket.ByteString as N
import           System.Exit
import           System.IO

import           Database.Memcache.Errors
import           Database.Memcache.Types


-- | Actions the mock server can take to a request.
data MockResponse
    = MR Response
    | CloseConnection
    | DelayMS Int MockResponse
    | Noop

-- | Run an IO action with a mock Memcached server running in the background,
-- killing it once done.
withMCServer :: Bool -> [MockResponse] -> IO () -> IO ()
withMCServer loop res m = bracket
    (mockMCServer loop res)
    (\tid -> killThread tid >> threadDelay 100000)
    (const m)

-- | New mock Memcached server that responds to each request with the specified
-- list of responses.
mockMCServer :: Bool -> [MockResponse] -> IO ThreadId
mockMCServer loop resp' = forkIO $ bracket 
    (N.socket N.AF_INET N.Stream N.defaultProtocol)
    (N.close)
    $ \sock -> do
        N.setSocketOption sock N.ReuseAddr 1
        let hints = N.defaultHints {
            N.addrFlags = [N.AI_PASSIVE]
          , N.addrSocketType = N.Stream
        }
        addr:_ <- N.getAddrInfo (Just hints) Nothing (Just "11211")
        N.bind sock $ N.addrAddress addr
        N.listen sock 10
        ref <- newIORef resp'
        acceptHandler sock ref
        when loop $ forever $ threadDelay 1000000
  
  where
    acceptHandler sock ref = do
        client <- fst <$> N.accept sock
        resp <- readIORef ref
        cont <- handle allErrors $ clientHandler client ref resp
        if cont
            then acceptHandler sock ref
            else return ()

    allErrors :: SomeException -> IO Bool
    allErrors = const $ return True

    clientHandler client ref []       = N.close client >> return False
    clientHandler client ref (r':resp) = do
      void $ recvReq client
      mrHandler r'
      where
        mrHandler r = case r of
            Noop            -> clientHandler client ref resp
            (MR mr)         -> sendRes client mr >> clientHandler client ref resp
            (DelayMS ms mr) -> do
                writeIORef ref resp -- client may reset connection
                threadDelay (ms * 1000)
                mrHandler mr
            CloseConnection -> do
                N.close client
                writeIORef ref resp
                return $ not $ null resp



sendRes :: N.Socket -> Response -> IO ()
sendRes s m = N.sendAll s (toByteString $ szResponse m)

recvReq :: N.Socket -> IO ()
recvReq s = do
    header <- recvAll s mEMCACHE_HEADER_SIZE mempty
    let h = runGet (dzHeader PktRequest) (L.fromChunks [header])
        bytesToRead = fromIntegral $ bodyLen h
    when (bytesToRead > 0) $
        void $ recvAll s bytesToRead mempty

recvAll :: N.Socket -> Int -> Builder -> IO B.ByteString
recvAll s 0 !acc = return $! toByteString acc
recvAll s !n !acc = do
    buf <- N.recv s n
    case B.length buf of
        0  -> throwIO errEOF
        bl | bl == n ->
            return $! (toByteString $! acc <> fromByteString buf)
        bl -> recvAll s (n - bl) (acc <> fromByteString buf)
  
  where
    errEOF :: MemcacheError
    errEOF = ProtocolError UnexpectedEOF { protocolError = "" }