{- -*- haskell -*- -}

-- |Message signing using asymmetric cipher and message digest
-- algorithm. This is an opposite of "OpenSSL.EVP.Verify".

module OpenSSL.EVP.Sign
    ( sign
    , signBS
    , signLBS
    )
    where

import qualified Data.ByteString.Char8 as B8
import qualified Data.ByteString.Internal as B8
import qualified Data.ByteString.Lazy.Char8 as L8
import           Control.Applicative ((<$>))
import           Foreign
import           Foreign.C
import           OpenSSL.EVP.Digest
import           OpenSSL.EVP.PKey
import           OpenSSL.EVP.Internal
import           OpenSSL.Utils

foreign import ccall unsafe "EVP_SignFinal"
  _SignFinal :: Ptr EVP_MD_CTX -> Ptr Word8 -> Ptr CUInt
             -> Ptr EVP_PKEY -> IO CInt

signFinal :: KeyPair k => DigestCtx -> k -> IO B8.ByteString
signFinal ctx k = do
  let maxLen = pkeySize k
  withDigestCtxPtr ctx $ \ ctxPtr ->
    withPKeyPtr' k $ \ pkeyPtr ->
      B8.createAndTrim maxLen $ \ bufPtr ->
        alloca $ \ bufLenPtr -> do
          failIf_ (/= 1) =<< _SignFinal ctxPtr bufPtr bufLenPtr pkeyPtr
          fromIntegral <$> peek bufLenPtr

-- |@'sign'@ generates a signature from a stream of data. The string
-- must not contain any letters which aren't in the range of U+0000 -
-- U+00FF.
sign :: KeyPair key =>
        Digest    -- ^ message digest algorithm to use
     -> key       -- ^ private key to sign the message digest
     -> String    -- ^ input string
     -> IO String -- ^ the result signature
sign md pkey input
    = fmap L8.unpack $ signLBS md pkey $ L8.pack input

-- |@'signBS'@ generates a signature from a chunk of data.
signBS :: KeyPair key =>
          Digest     -- ^ message digest algorithm to use
       -> key        -- ^ private key to sign the message digest
       -> B8.ByteString -- ^ input string
       -> IO B8.ByteString -- ^ the result signature
signBS md pkey input
    = do ctx <- digestStrictly md input
         signFinal ctx pkey

-- |@'signLBS'@ generates a signature from a stream of data.
signLBS :: KeyPair key =>
           Digest        -- ^ message digest algorithm to use
        -> key           -- ^ private key to sign the message digest
        -> L8.ByteString -- ^ input string
        -> IO L8.ByteString -- ^ the result signature
signLBS md pkey input
    = do ctx <- digestLazily md input
         sig <- signFinal ctx pkey
         return $ L8.fromChunks [sig]