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{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE PatternGuards #-}
module GnuPGAgent
    ( session
    , Query(..)
    , QueryMode(..)
    , getPassphrase
    , clearPassphrase
    , quit
    , key_nbits) where

import Debug.Trace
import Control.Monad
import Data.Char
import Data.OpenPGP
import Data.OpenPGP.Util
import Network.Socket
import System.Directory
import System.Environment
import System.IO
import Text.Printf
#if defined(VERSION_memory)
import qualified Data.ByteString.Char8 as S8
import Data.ByteArray.Encoding
#elif defined(VERSION_dataenc)
import qualified Codec.Binary.Base16 as Base16
#endif
import LengthPrefixedBE
import qualified Data.ByteString.Lazy as L
#if defined(VERSION_hourglass)
import Data.Hourglass
#else
import Data.Time.Calendar
import Data.Time.Clock
import Data.Time.Clock.POSIX
#endif
import Data.Word

data GnuPGAgent = GnuPGAgent { agentHandle :: Handle }

session = do
    envhomedir Nothing gpgHomeSpec >>= \case
        Just gpghome -> do
            sock <- socket AF_UNIX Stream defaultProtocol
            connect sock (SockAddrUnix (gpghome ++ "/S.gpg-agent"))
            agent <- socketToHandle sock ReadWriteMode
            hSetBuffering agent LineBuffering
            lookupEnv "DISPLAY" >>= \case
                Just display -> do hPutStrLn agent ("option putenv DISPLAY="++display)
                                   _ <- hGetLine agent
                                   return ()
                Nothing      -> return ()
            -- TODO: GPG_TTY
            return $ Just $ GnuPGAgent agent
        Nothing -> do
            hPutStrLn stderr "Unable to find home directory."
            return Nothing

percentPlusEscape :: String -> String
percentPlusEscape s = do
    c <- s
    case c of
        ' '         -> "+"
        '+'         -> "%2B"
        '"'         -> "%22"
        '%'         -> "%25"
        _ | c < ' ' -> printf "%%%02X" (ord c)
        _           -> return c

clearPassphrase agent key = do
    let cmd = "clear_passphrase --mode=normal "++fingerprint key
    hPutStrLn (agentHandle agent) cmd

data Query = Query
    { queryPacket  :: Packet
    , queryUID     :: String
    , queryMainKey :: Maybe Packet
    }
 deriving Show

data QueryMode = AskNot | AskAgain String | AskExisting | AskNew
 deriving (Show,Eq,Ord)

getPassphrase :: GnuPGAgent -> QueryMode -> Query -> IO (Maybe String)
getPassphrase agent ask (Query key uid masterkey) = do
    let (er0,pr,desc) = prompts key uid masterkey
        (er,askopt) = case ask of
                        AskNot         -> (er0,"--no-ask ")
                        AskAgain ermsg -> (ermsg,"")
                        AskExisting    -> (er0,"")
                        AskNew         -> (er0,"--repeat=1 ")
        cmd = "get_passphrase "++askopt++fingerprint key++" "++unwords (map percentPlusEscape [er,pr,desc])
    hPutStrLn stderr $ "gpg-agent <- " ++ cmd
    hPutStrLn (agentHandle agent) cmd
    r0 <- hGetLine (agentHandle agent)
    -- hPutStrLn stderr $ "agent says: " ++ r0
    case takeWhile (/=' ') r0 of
        "OK" -> hGetLine (agentHandle agent) >>= unhex . drop 3
            where
#if defined(VERSION_memory)
                unhex hx = case convertFromBase Base16 (S8.pack hx) of
                            Left e -> do
                                -- Useful for debugging but insecure generally ;)
                                -- putStrLn $ "convertFromBase error for input "++show hx++": "++show e
                                return Nothing
                            Right bs -> return $ Just $ S8.unpack bs
#elif defined(VERSION_dataenc)
                unhex hx = maybe (return () {- putStrLn $ "dataenc error for input "++show hx -})
                                 return
                                 $ fmap (map $ chr . fromIntegral) $ Base16.decode hx
#endif
        "ERR" -> return Nothing

quit (GnuPGAgent h) = hClose h

prompts :: Packet -> String -> Maybe Packet -> (String,String,String)
prompts key uid masterkey = ("X","X",atext)
 where
    atext = printf (concat [ "Please enter the passphrase to unlock the"
                           , " secret key for the OpenPGP certificate:\n"
                           , "\"%s\"\n"
                           , "%d-bit %s key, ID %s,\n"
                           , "created %s%s.\n"])
                   uid
                   (key_nbits key) algo_name (keystr key)
                   timestr maink

    maink
        | Just k <- masterkey = printf " (main key ID %s)" (drop 32 $ fingerprint k)
        | otherwise           = ""

    algo_name =
        case key_algorithm key of
            a | a `elem` [RSA,RSA_E,RSA_S] -> "RSA"
            ELGAMAL                        -> "ELG" -- also PUBKEY_ALGO_ELGAMAL_E
            DSA                            -> "DSA"
            ECDSA                          -> "ECDSA"
            ECC                            -> "ECDH"
            _                              -> "?" -- also "EDDSA";


    keystr k = drop 32 $ fingerprint k -- FCD7BFB7

    timestr = timeString $ timestamp key -- 2014-01-04

data HomeDir = HomeDir { homevar :: String, appdir :: String }
gpgHomeSpec :: HomeDir
gpgHomeSpec = HomeDir
    { homevar = "GNUPGHOME"
    , appdir  = ".gnupg"
    }

envhomedir opt home = do
        gnupghome <- fmap (mfilter (/="")) $ lookupEnv (homevar home)
        homed <- fmap (mfilter (/="") . Just) getHomeDirectory
        let homegnupg = (++('/':(appdir home))) <$> homed
        let val = (opt `mplus` gnupghome `mplus` homegnupg)
        return $ val


timeString :: Word32 -> String
timeString t = printf "%d-%d-%d" year month day
 where
#if defined(VERSION_hourglass)
    Date year m day = timeFromElapsed (Elapsed (Seconds $ fromIntegral t))
    month = fromEnum m + 1
#else
    (year,month,day) = toGregorian . utctDay $ posixSecondsToUTCTime (realToFrac t)
#endif

key_nbits :: Packet -> Int
key_nbits p@(SecretKeyPacket {}) = _key_nbits (key_algorithm p) (key p)
key_nbits p@(PublicKeyPacket {}) = _key_nbits (key_algorithm p) (key p)
key_nbits _ = 0

_key_nbits :: KeyAlgorithm -> [(Char,MPI)] -> Int
_key_nbits RSA     toks | Just n <- lookup 'n' toks = mpi_nbits n
_key_nbits DSA     toks | Just n <- lookup 'p' toks = mpi_nbits n
_key_nbits ECDSA   toks | Just n <- lookup 'c' toks = curve_oid_nbits n
_key_nbits ELGAMAL toks | Just n <- lookup 'p' toks = mpi_nbits n
_key_nbits _ _ = 0
-- unimplemented: RSA_E RSA_S ECC DH / KeyAlgorithm Word8

curve_oid_nbits :: MPI -> Int
curve_oid_nbits (MPI 0x2a8648ce3d030107 ) = 256 -- SEC p256r1 ( NIST P-256 )
curve_oid_nbits (MPI 0x2B81040022 )       = 384 -- SEC p384r1 ( NIST P-384 )
curve_oid_nbits (MPI 0x2B81040023 )       = 521 -- SEC p521r1 ( NIST P-521 )
curve_oid_nbits (MPI 0x2b8104000a )       = 256 -- SEC p256k1 ( bitcoin curve )
curve_oid_nbits n = trace ("Unknown curve: "++ show n) 0


mpi_nbits (MPI n) = 8 * fromIntegral len
 where
    len = case encode_bigendian n of
            b | L.head b == 0x0 -> L.length b - 1
              | otherwise       -> L.length b