-- | https://stripe.com/docs/webhooks/signatures#verify-manually
module Stripe.Signature
  ( Sig (..),
    isSigValid,
    digest,
    signedPayload,
    natBytes,
    parseSig,
  )
where

import Crypto.Hash.SHA256 qualified
import Data.ByteString (ByteString)
import Data.ByteString.Base16 qualified as Base16
import Data.List qualified
import Data.Maybe qualified
import Data.String qualified
import Data.Text (Text)
import Data.Text qualified as Text
import Data.Text.Encoding qualified as Text
import Numeric.Natural (Natural)
import Stripe.Concepts (WebhookSecretKey (..))
import Text.Read qualified

isSigValid :: Sig -> WebhookSecretKey -> ByteString -> Bool
isSigValid :: Sig -> WebhookSecretKey -> ByteString -> Bool
isSigValid Sig
x WebhookSecretKey
secret ByteString
body =
  forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
Data.List.any (forall a. Eq a => a -> a -> Bool
(==) ByteString
correctDigest) (Sig -> [ByteString]
sigV1 Sig
x)
  where
    correctDigest :: ByteString
correctDigest = WebhookSecretKey -> Natural -> ByteString -> ByteString
digest WebhookSecretKey
secret (Sig -> Natural
sigTime Sig
x) ByteString
body

digest :: WebhookSecretKey -> Natural -> ByteString -> ByteString
digest :: WebhookSecretKey -> Natural -> ByteString -> ByteString
digest (WebhookSecretKey ByteString
secret) Natural
time ByteString
body =
  ByteString -> ByteString -> ByteString
Crypto.Hash.SHA256.hmac ByteString
secret (Natural -> ByteString -> ByteString
signedPayload Natural
time ByteString
body)

signedPayload :: Natural -> ByteString -> ByteString
signedPayload :: Natural -> ByteString -> ByteString
signedPayload Natural
time ByteString
body =
  forall a. Monoid a => [a] -> a
mconcat
    [ Natural -> ByteString
natBytes Natural
time,
      String -> ByteString
encodeAscii String
".",
      ByteString
body
    ]

-- | Convert a natural number to the ASCII encoding of its decimal
-- representation.
natBytes :: Natural -> ByteString
natBytes :: Natural -> ByteString
natBytes = String -> ByteString
encodeAscii forall b c a. (b -> c) -> (a -> b) -> a -> c
. (forall a. Show a => a -> String
show :: Natural -> String)

encodeAscii :: String -> ByteString
encodeAscii :: String -> ByteString
encodeAscii = forall a. IsString a => String -> a
Data.String.fromString

-- | The relevant bits of data extracted from the Stripe signature header.
data Sig = Sig
  { Sig -> Natural
sigTime :: Natural,
    Sig -> [ByteString]
sigV1 :: [ByteString]
  }

-- | Parse the Stripe signature header, returning 'Nothing' if parsing fails.
parseSig :: Text -> Maybe Sig
parseSig :: Text -> Maybe Sig
parseSig Text
txt =
  let parts :: [(Text, Text)]
      parts :: [(Text, Text)]
parts = Text -> [(Text, Text)]
splitSig Text
txt
   in do
        Natural
time <-
          forall a b. Eq a => a -> [(a, b)] -> Maybe b
Data.List.lookup (String -> Text
Text.pack String
"t") [(Text, Text)]
parts
            forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
>>= (String -> Maybe Natural
readNatural forall b c a. (b -> c) -> (a -> b) -> a -> c
. Text -> String
Text.unpack)

        let v1 :: [ByteString]
v1 =
              forall a b. (a -> Maybe b) -> [a] -> [b]
Data.Maybe.mapMaybe
                ( \(Text
k, Text
v) ->
                    if Text
k forall a. Eq a => a -> a -> Bool
== String -> Text
Text.pack String
"v1"
                      then Text -> Maybe ByteString
decodeHex Text
v
                      else forall a. Maybe a
Nothing
                )
                [(Text, Text)]
parts

        forall (f :: * -> *) a. Applicative f => a -> f a
pure Sig {sigTime :: Natural
sigTime = Natural
time, sigV1 :: [ByteString]
sigV1 = [ByteString]
v1}

splitSig :: Text -> [(Text, Text)]
splitSig :: Text -> [(Text, Text)]
splitSig =
  forall a. [Maybe a] -> [a]
Data.Maybe.catMaybes
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (Text -> Text -> Maybe (Text, Text)
split2 (String -> Text
Text.pack String
"="))
    forall b c a. (b -> c) -> (a -> b) -> a -> c
. Text -> Text -> [Text]
Text.splitOn (String -> Text
Text.pack String
",")

split2 :: Text -> Text -> Maybe (Text, Text)
split2 :: Text -> Text -> Maybe (Text, Text)
split2 Text
pat Text
src =
  let (Text
x, Text
y) = Text -> Text -> (Text, Text)
Text.breakOn Text
pat Text
src
      y' :: Text
y' = Int -> Text -> Text
Text.drop (Text -> Int
Text.length Text
pat) Text
y
   in if Text -> Bool
Text.null Text
y then forall a. Maybe a
Nothing else forall a. a -> Maybe a
Just (Text
x, Text
y')

-- | Parse a number consisting of one or more digits 0 through 9.
readNatural :: String -> Maybe Natural
readNatural :: String -> Maybe Natural
readNatural = forall a. Read a => String -> Maybe a
Text.Read.readMaybe

-- | Decodes hexadecimal text as a byte string. The result is a 'Just' value iff
-- the text contains an even number of characters and consists only of the digits
-- @0@ through @9@ and letters @a@ through @f@.
decodeHex :: Text -> Maybe ByteString
decodeHex :: Text -> Maybe ByteString
decodeHex = forall a c b. (a -> c) -> (b -> c) -> Either a b -> c
either (forall a b. a -> b -> a
const forall a. Maybe a
Nothing) forall a. a -> Maybe a
Just forall b c a. (b -> c) -> (a -> b) -> a -> c
. ByteString -> Either String ByteString
Base16.decode forall b c a. (b -> c) -> (a -> b) -> a -> c
. Text -> ByteString
Text.encodeUtf8