-- Internal.hs: private utility functions and such
-- Copyright © 2012-2019  Clint Adams
-- This software is released under the terms of the Expat license.
-- (See the LICENSE file).
{-# LANGUAGE OverloadedStrings #-}

module Codec.Encryption.OpenPGP.Internal
  ( countBits
  , PktStreamContext(..)
  , issuer
  , issuerFP
  , emptyPSC
  , pubkeyToMPIs
  , multiplicativeInverse
  , curveoidBSToCurve
  , curveToCurveoidBS
  , point2BS
  , curveoidBSToEdSigningCurve
  , edSigningCurveToCurveoidBS
  , curve2Curve
  , curveFromCurve
  ) where

import Crypto.Number.Serialize (i2osp, os2ip)
import qualified Crypto.PubKey.DSA as DSA
import qualified Crypto.PubKey.ECC.ECDSA as ECDSA
import qualified Crypto.PubKey.ECC.Types as ECCT
import qualified Crypto.PubKey.RSA as RSA

import Data.Bits (testBit)
import qualified Data.ByteString as B
import Data.ByteString.Lazy (ByteString)
import qualified Data.ByteString.Lazy as BL
import Data.List (find)
import Data.Word (Word16, Word8)

import Codec.Encryption.OpenPGP.Ontology (isIssuerSSP, isIssuerFPSSP, isSigCreationTime)
import Codec.Encryption.OpenPGP.Types

countBits :: ByteString -> Word16
countBits bs
  | BL.null bs = 0
  | otherwise =
    fromIntegral (BL.length bs * 8) - fromIntegral (go (BL.head bs) 7)
  where
    go :: Word8 -> Int -> Word8
    go _ 0 = 7
    go n b =
      if testBit n b
        then 7 - fromIntegral b
        else go n (b - 1)

data PktStreamContext =
  PktStreamContext
    { lastLD :: Pkt
    , lastUIDorUAt :: Pkt
    , lastSig :: Pkt
    , lastPrimaryKey :: Pkt
    , lastSubkey :: Pkt
    }

emptyPSC :: PktStreamContext
emptyPSC =
  PktStreamContext
    (OtherPacketPkt 0 "lastLD placeholder")
    (OtherPacketPkt 0 "lastUIDorUAt placeholder")
    (OtherPacketPkt 0 "lastSig placeholder")
    (OtherPacketPkt 0 "lastPrimaryKey placeholder")
    (OtherPacketPkt 0 "lastSubkey placeholder")

issuer :: Pkt -> Maybe EightOctetKeyId
issuer (SignaturePkt (SigV4 _ _ _ _ usubs _ _)) =
  fmap (\(SigSubPacket _ (Issuer i)) -> i) (find isIssuerSSP usubs)
issuer _ = Nothing

issuerFP :: Pkt -> Maybe TwentyOctetFingerprint
issuerFP (SignaturePkt (SigV4 _ _ _ hsubs _ _ _)) =
  fmap (\(SigSubPacket _ (IssuerFingerprint _ i)) -> i) (find isIssuerFPSSP hsubs)
issuerFP _ = Nothing

pubkeyToMPIs :: PKey -> [MPI]
pubkeyToMPIs (RSAPubKey (RSA_PublicKey k)) =
  [MPI (RSA.public_n k), MPI (RSA.public_e k)]
pubkeyToMPIs (DSAPubKey (DSA_PublicKey k)) =
  [ pkParams DSA.params_p
  , pkParams DSA.params_q
  , pkParams DSA.params_g
  , MPI . DSA.public_y $ k
  ]
  where
    pkParams f = MPI . f . DSA.public_params $ k
pubkeyToMPIs (ElGamalPubKey p g y) = [MPI p, MPI g, MPI y]
pubkeyToMPIs (ECDHPubKey (ECDSAPubKey (ECDSA_PublicKey (ECDSA.PublicKey _ q))) _ _) =
  [MPI (os2ip (point2BS q))]
pubkeyToMPIs (ECDHPubKey (EdDSAPubKey _ (EPoint x)) _ _) = [MPI x]
pubkeyToMPIs (ECDSAPubKey ((ECDSA_PublicKey (ECDSA.PublicKey _ q)))) =
  [MPI (os2ip (point2BS q))]
pubkeyToMPIs (EdDSAPubKey _ (EPoint x)) = [MPI x]

multiplicativeInverse :: Integral a => a -> a -> a
multiplicativeInverse _ 1 = 1
multiplicativeInverse q p = (n * q + 1) `div` p
  where
    n = p - multiplicativeInverse p (q `mod` p)

curveoidBSToCurve :: B.ByteString -> Either String ECCCurve
curveoidBSToCurve oidbs
  | B.pack [0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x03, 0x01, 0x07] == oidbs =
    Right $ NISTP256 -- ECCT.getCurveByName ECCT.SEC_p256r1
  | B.pack [0x2B, 0x81, 0x04, 0x00, 0x22] == oidbs = Right $ NISTP384 -- ECCT.getCurveByName ECCT.SEC_p384r1
  | B.pack [0x2B, 0x81, 0x04, 0x00, 0x23] == oidbs = Right $ NISTP521 -- ECCT.getCurveByName ECCT.SEC_p521r1
  | B.pack [0x2B, 0x06, 0x01, 0x04, 0x01, 0x97, 0x55, 0x01, 0x05, 0x01] == oidbs =
    Right Curve25519
  | otherwise = Left $ concat ["unknown curve (...", show (B.unpack oidbs), ")"]

curveToCurveoidBS :: ECCCurve -> Either String B.ByteString
curveToCurveoidBS NISTP256 =
  Right $ B.pack [0x2A, 0x86, 0x48, 0xCE, 0x3D, 0x03, 0x01, 0x07]
curveToCurveoidBS NISTP384 = Right $ B.pack [0x2B, 0x81, 0x04, 0x00, 0x22]
curveToCurveoidBS NISTP521 = Right $ B.pack [0x2B, 0x81, 0x04, 0x00, 0x23]
curveToCurveoidBS Curve25519 =
  Right $ B.pack [0x2B, 0x06, 0x01, 0x04, 0x01, 0x97, 0x55, 0x01, 0x05, 0x01]
curveToCurveoidBS _ = Left "unknown curve"

point2BS :: ECCT.PublicPoint -> B.ByteString
point2BS (ECCT.Point x y) = B.concat [B.singleton 0x04, i2osp x, i2osp y] -- FIXME: check for length equality?
point2BS ECCT.PointO = error "FIXME: point at infinity"

curveoidBSToEdSigningCurve :: B.ByteString -> Either String EdSigningCurve
curveoidBSToEdSigningCurve oidbs
  | B.pack [0x2B, 0x06, 0x01, 0x04, 0x01, 0xDA, 0x47, 0x0F, 0x01] == oidbs =
    Right Ed25519
  | otherwise =
    Left $
    concat ["unknown Edwards signing curve (...", show (B.unpack oidbs), ")"]

edSigningCurveToCurveoidBS :: EdSigningCurve -> Either String B.ByteString
edSigningCurveToCurveoidBS Ed25519 =
  Right $ B.pack [0x2B, 0x06, 0x01, 0x04, 0x01, 0xDA, 0x47, 0x0F, 0x01]

curve2Curve :: ECCCurve -> ECCT.Curve
curve2Curve NISTP256 = ECCT.getCurveByName ECCT.SEC_p256r1
curve2Curve NISTP384 = ECCT.getCurveByName ECCT.SEC_p384r1
curve2Curve NISTP521 = ECCT.getCurveByName ECCT.SEC_p521r1

curveFromCurve :: ECCT.Curve -> ECCCurve
curveFromCurve c
  | c == ECCT.getCurveByName ECCT.SEC_p256r1 = NISTP256
  | c == ECCT.getCurveByName ECCT.SEC_p384r1 = NISTP384
  | c == ECCT.getCurveByName ECCT.SEC_p521r1 = NISTP521