{-# LANGUAGE KindSignatures #-}
module CryptoTransport
    ( parseNetCrypto
    , encodeNetCrypto
    -- CryptoTransport
    , NetCrypto(..)
    , CryptoData(..)
    , CryptoMessage(..)
    , CryptoPacket(..)
    , HandshakeData(..)
    , Handshake(..)
    ) where

import ToxCrypto
import DHTTransport (Cookie)

import Network.Socket
import Data.ByteString
import Data.Word
import Crypto.Hash

data NetCrypto
    = NetHandshake (Handshake Encrypted)
    | NetCrypto (CryptoPacket Encrypted)

parseNetCrypto :: ByteString -> SockAddr -> Either String (NetCrypto, SockAddr)
parseNetCrypto _ _  = Left "TODO: parseNetCrypto"

encodeNetCrypto :: NetCrypto -> SockAddr -> (ByteString, SockAddr)
encodeNetCrypto _ _ = _todo

data Handshake (f :: * -> *) = Handshake
    { handshakeCookie :: Cookie
    , handshakeNonce :: Nonce24
    , hadshakeData :: f HandshakeData
    }

data HandshakeData = HandshakeData
    { baseNonce :: Nonce24
    , sessionKey :: PublicKey
    , cookieHash :: Digest SHA512
    , otherCookie :: Cookie
    }

data CryptoPacket (f :: * -> *) = CryptoPacket
    { pktNonce :: Word16
    , pktData :: f CryptoData
    }

data CryptoData = CryptoData
    { -- | [our recvbuffers buffer_start, (highest packet number handled + 1), (big endian)]
      bufferStart :: Word32
      -- | [  uint32_t packet number if lossless
      --   , sendbuffer buffer_end  if lossy   , (big endian)]
    , bufferEnd :: Word32
      -- | [data]
    , bufferData :: CryptoMessage
    }

-- TODO: Flesh this out.
data CryptoMessage      -- First byte indicates data
    = Padding           -- ^ 0 padding (skipped until we hit a non zero (data id) byte)
    | PacketRequest     -- ^ 1 packet request packet (lossy packet)
    | KillPacket        -- ^ 2 connection kill packet (lossy packet)
    | UnspecifiedPacket -- ^ 3+ unspecified
    | MessengerLossless -- ^ 16+  reserved for Messenger usage (lossless packets)
    | MessengerLossy    -- ^ 192+ reserved for Messenger usage (lossy packets)
    | Messenger255      -- ^ 255 reserved for Messenger usage (lossless packet)



-- --> CookieRequest WithoutCookie
-- <-- CookieResponse CookieAddress
-- --> Handshake CookieAddress
-- <-- Handshake CookieAddress

-- Handshake packet:
--    [uint8_t 26] (0x1a)
--    [Cookie]
--    [nonce (24 bytes)]
--    [Encrypted message containing:
--        [24 bytes base nonce]
--        [session public key of the peer (32 bytes)]
--        [sha512 hash of the entire Cookie sitting outside the encrypted part]
--        [Other Cookie (used by the other to respond to the handshake packet)]
--    ]

-- cookie response packet (161 bytes):
--
--     [uint8_t 25]
--     [Random nonce (24 bytes)]
--     [Encrypted message containing:
--         [Cookie]
--         [uint64_t echo id (that was sent in the request)]
--     ]
--
--     Encrypted message is encrypted with the exact same symmetric key as the
--     cookie request packet it responds to but with a different nonce.
--     (Encrypted message is encrypted with reqesters's DHT private key,
--     responders's DHT public key and the nonce.)
--
--     Since we don't receive the public key, we will need to lookup the key by
--     the SockAddr... I don't understand why the CookieResponse message is
--     special this way.  TODO: implement a multimap (SockAddr -> SharedSecret)
--     and wrap cookie queries with store/delete.  TODO: Should the entire
--     SharedScret cache be keyed on only SockAddr ?  Perhaps the secret cache
--     should be (NodeId -> Secret) and the cookie-request map should be
--     (SockAddr -> NodeId)

-- Encrypted packets:
--
--  Length    Contents
-- :---------:--------------------------------------------------------------
--  `1`       `uint8_t` (0x1b)
--  `2`       `uint16_t` The last 2 bytes of the nonce used to encrypt this
--  variable   Payload
--
-- The payload is encrypted with the session key and 'base nonce' set by the
-- receiver in their handshake + packet number (starting at 0, big endian math).