-- |
--   Copyright   :  (c) Sam T. 2013
--   License     :  MIT
--   Maintainer  :  pxqr.sta@gmail.com
--   Stability   :  experimental
--   Portability :  portable
--
--   In order to establish the connection between peers we should send
--   'Handshake' message. The 'Handshake' is a required message and
--   must be the first message transmitted by the peer to the another
--   peer.
--
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards #-}
module Network.BitTorrent.PeerWire.Handshake
       ( Handshake(..), handshakeCaps
       , handshake
       , ppHandshake
       , defaultHandshake, defaultBTProtocol, defaultReserved
       , handshakeMaxSize
       ) where

import Control.Applicative
import Control.Monad
import Control.Exception
import Data.Word
import           Data.ByteString (ByteString)
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as BC
import Data.Serialize as S
import Text.PrettyPrint

import Network
import Network.Socket.ByteString

import Data.Torrent
import Network.BitTorrent.Extension
import Network.BitTorrent.Peer



data Handshake = Handshake {
    -- | Identifier of the protocol.
    hsProtocol    :: ByteString

    -- | Reserved bytes used to specify supported BEP's.
  , hsReserved    :: Capabilities

    -- | Info hash of the info part of the metainfo file. that is
    -- transmitted in tracker requests. Info hash of the initiator
    -- handshake and response handshake should match, otherwise
    -- initiator should break the connection.
    --
  , hsInfoHash    :: InfoHash

    -- | Peer id of the initiator. This is usually the same peer id
    -- that is transmitted in tracker requests.
    --
  , hsPeerID      :: PeerID

  } deriving (Show, Eq)

instance Serialize Handshake where
  put hs = do
    putWord8 (fromIntegral (B.length (hsProtocol hs)))
    putByteString (hsProtocol hs)
    putWord64be   (hsReserved hs)
    put (hsInfoHash hs)
    put (hsPeerID hs)

  get = do
    len  <- getWord8
    Handshake <$> getBytes (fromIntegral len)
              <*> getWord64be
              <*> get
              <*> get


handshakeCaps :: Handshake -> Capabilities
handshakeCaps = hsReserved

-- | Format handshake in human readable form.
ppHandshake :: Handshake -> Doc
ppHandshake Handshake {..} =
  text (BC.unpack hsProtocol) <+> ppClientInfo (clientInfo hsPeerID)

-- | Get handshake message size in bytes from the length of protocol string.
handshakeSize :: Word8 -> Int
handshakeSize n = 1 + fromIntegral n + 8 + 20 + 20

-- | Maximum size of handshake message in bytes.
handshakeMaxSize :: Int
handshakeMaxSize = handshakeSize 255

-- | Default protocol string "BitTorrent protocol" as is.
defaultBTProtocol :: ByteString
defaultBTProtocol = "BitTorrent protocol"

-- | Default reserved word is 0.
defaultReserved :: Word64
defaultReserved = 0

-- | Length of info hash and peer id is unchecked, so it /should/ be equal 20.
defaultHandshake :: InfoHash -> PeerID -> Handshake
defaultHandshake = Handshake defaultBTProtocol defaultReserved

-- | Handshaking with a peer specified by the second argument.
handshake :: Socket -> Handshake -> IO Handshake
handshake sock hs = do
    sendAll sock (S.encode hs)

    header <- recv sock 1
    when (B.length header == 0) $
      throw $ userError "Unable to receive handshake."

    let protocolLen = B.head header
    let restLen     = handshakeSize protocolLen - 1
    body <- recv sock restLen
    let resp = B.cons protocolLen body

    case checkIH (S.decode resp) of
      Right hs' -> return hs'
      Left msg  -> throw $ userError msg
  where
    checkIH (Right hs')
      | hsInfoHash hs /= hsInfoHash hs' = Left "Handshake info hash do not match."
    checkIH x = x