{-# LANGUAGE DerivingStrategies #-}

-- | P256 cryptographic primitives.
--
-- This module is mostly a stub, it doesn't implement actual crypto.
-- TODO (#18) implement crypto properly.

module Tezos.Crypto.P256
  ( -- * Cryptographic primitive types
    PublicKey (..)
  , SecretKey
  , Signature (..)
  , detSecretKey
  , toPublic

  -- * Raw bytes (no checksums, tags or anything)
  , publicKeyToBytes
  , mkPublicKey
  , publicKeyLengthBytes
  , signatureToBytes
  , mkSignature
  , signatureLengthBytes

  -- * Formatting and parsing
  , formatPublicKey
  , mformatPublicKey
  , parsePublicKey
  , formatSignature
  , mformatSignature
  , parseSignature

  -- * Signing
  , checkSignature
  ) where

import Crypto.Random (getRandomBytes)
import Data.ByteArray (ByteArray, ByteArrayAccess)
import qualified Data.ByteArray as BA
import qualified Data.ByteString as BS
import Fmt (Buildable, build)
import Test.QuickCheck (Arbitrary(..), vector)

import Michelson.Text
import Tezos.Crypto.Util

----------------------------------------------------------------------------
-- Types, instances, conversions
----------------------------------------------------------------------------

-- | P256 public cryptographic key.
newtype PublicKey = PublicKey
  { unPublicKey :: ByteString
  } deriving stock (Show, Eq)

instance Arbitrary PublicKey where
  arbitrary = toPublic <$> arbitrary

-- | P256 secret cryptographic key.
newtype SecretKey = SecretKey
  { unSecretKey :: ByteString
  } deriving stock (Show, Eq)

-- | Deterministicaly generate a secret key from seed.
detSecretKey :: ByteString -> SecretKey
detSecretKey seed =
  SecretKey $ deterministic seed $ getRandomBytes publicKeyLengthBytes

instance Arbitrary SecretKey where
  arbitrary = detSecretKey . BS.pack <$> vector 32

-- | Create a public key from a secret key.
toPublic :: SecretKey -> PublicKey
toPublic = PublicKey . unSecretKey

-- | P256 cryptographic signature.
newtype Signature = Signature
  { unSignature :: ByteString
  } deriving stock (Show, Eq)

instance Arbitrary Signature where
  arbitrary = Signature . BS.pack <$> replicateM signatureLengthBytes arbitrary

----------------------------------------------------------------------------
-- Conversion to/from raw bytes (no checksums, tags or anything)
----------------------------------------------------------------------------

-- | Convert a 'PublicKey' to raw bytes.
--
-- TODO (#18): implement properly.
publicKeyToBytes :: forall ba. ByteArray ba => PublicKey -> ba
publicKeyToBytes = BA.convert . unPublicKey

-- | Make a 'PublicKey' from raw bytes.
--
-- TODO (#18): implement properly.
mkPublicKey :: ByteArrayAccess ba => ba -> Either CryptoParseError PublicKey
mkPublicKey ba
  | l == publicKeyLengthBytes =
    Right $ PublicKey (BA.convert ba)
  | otherwise =
    Left $ CryptoParseUnexpectedLength "public key" l
  where
    l = BA.length ba

publicKeyLengthBytes :: Integral n => n
publicKeyLengthBytes = 33

-- | Convert a 'PublicKey' to raw bytes.
--
-- TODO (#18): implement properly.
signatureToBytes :: ByteArray ba => Signature -> ba
signatureToBytes = BA.convert . unSignature

-- | Make a 'Signature' from raw bytes.
--
-- TODO (#18): implement properly.
mkSignature :: ByteArray ba => ba -> Either CryptoParseError Signature
mkSignature ba
  | l == signatureLengthBytes =
    Right $ Signature (BA.convert ba)
  | otherwise =
    Left $ CryptoParseUnexpectedLength "signature" l
  where
    l = BA.length ba

signatureLengthBytes :: Integral n => n
signatureLengthBytes = 64

----------------------------------------------------------------------------
-- Magic bytes
----------------------------------------------------------------------------

publicKeyTag :: ByteString
publicKeyTag = "\003\178\139\127"

signatureTag :: ByteString
signatureTag = "\054\240\044\052"

----------------------------------------------------------------------------
-- Formatting
----------------------------------------------------------------------------

formatPublicKey :: PublicKey -> Text
formatPublicKey = formatImpl @ByteString publicKeyTag . publicKeyToBytes

mformatPublicKey :: PublicKey -> MText
mformatPublicKey = mkMTextUnsafe . formatPublicKey

instance Buildable PublicKey where
  build = build . formatPublicKey

parsePublicKey :: Text -> Either CryptoParseError PublicKey
parsePublicKey = parseImpl publicKeyTag mkPublicKey

formatSignature :: Signature -> Text
formatSignature = formatImpl @ByteString signatureTag . signatureToBytes

mformatSignature :: Signature -> MText
mformatSignature = mkMTextUnsafe . formatSignature

instance Buildable Signature where
  build = build . formatSignature

parseSignature :: Text -> Either CryptoParseError Signature
parseSignature = parseImpl signatureTag mkSignature

----------------------------------------------------------------------------
-- Signing
----------------------------------------------------------------------------

-- | Check that a sequence of bytes has been signed with a given key.
checkSignature :: PublicKey -> Signature -> ByteString -> Bool
checkSignature _ _ _ = False