server/src/Game.hs

{-# LANGUAGE NamedFieldPuns #-}
module Game (
      exportGame
    , new
    , play
  ) where

import qualified App (T, get)
import Control.Monad.Except (runExceptT)
import Control.Monad.Reader (lift)
import Control.Monad.Writer (runWriterT)
import qualified Crypto.Saltine.Class as Saltine (IsEncoding(..))
import Crypto.Saltine.Core.SecretBox (newNonce, secretbox, secretboxOpen)
import Crypto.Saltine.Core.Sign (signDetached, signVerifyDetached)
import Data.Aeson (ToJSON, eitherDecode', encode)
import Data.ByteString (ByteString)
import Data.ByteString.Lazy (fromStrict, toStrict)
import Data.Map ((!), Map, mapWithKey)
import qualified Hanafuda (Pack)
import Hanafuda.KoiKoi (Game, Mode(..), Player, PlayerID, Players)
import qualified Hanafuda.KoiKoi as KoiKoi (
    Action, Game(..), Move(..), play, new
  )
import Hanafuda.Message (PrivateState(..), PublicGame(..), PublicPlayer(..), PublicState(..))
import qualified Hanafuda.Player as Player (Player(..), Players(..), get)
import Keys (T(..))
import qualified Keys (public, secret)
import qualified Server (T(..))

new :: (PlayerID, PlayerID) -> App.T Game
new (for, to) = lift $ KoiKoi.new (for, to) WholeYear

exportPlayers :: Game -> Map PlayerID Player
exportPlayers game =
  let (Player.Players players) = KoiKoi.players game in
  players

privateState :: Game -> PrivateState
privateState game = PrivateState {
      hands = Player.hand <$> players
    , deck = KoiKoi.deck game
  }
  where
    Player.Players players = KoiKoi.players game

getHand :: PlayerID -> Players -> Hanafuda.Pack
getHand playerID = Player.hand . (Player.get playerID)

publicPlayer :: Player -> PublicPlayer
publicPlayer player = PublicPlayer {
      meld = Player.meld player
    , yakus = Player.yakus player
  }

privatePlayer :: Map PlayerID PublicPlayer -> PlayerID -> Hanafuda.Pack -> Player
privatePlayer publicPlayers playerID hand = Player.Player {
      Player.hand
    , Player.meld = meld (publicPlayers ! playerID)
    , Player.yakus = yakus (publicPlayers ! playerID)
  }

publicState :: Game -> PublicState
publicState game = PublicState {
      mode = KoiKoi.mode game
    , scores = KoiKoi.scores game
    , month = KoiKoi.month game
    , nextPlayer = KoiKoi.nextPlayer game
    , players = publicPlayer <$> exportPlayers game
    , playing = KoiKoi.playing game
    , winning = KoiKoi.winning game
    , oyake = KoiKoi.oyake game
    , river = KoiKoi.river game
    , step = KoiKoi.step game
    , trick = KoiKoi.trick game
    , turns = 24 - length (KoiKoi.deck game)
    , rounds = KoiKoi.rounds game
  }

exportGame :: PlayerID -> Game -> App.T PublicGame
exportGame playerID game = do
  Keys.T {encrypt, sign} <- App.get Server.keys
  n <- lift newNonce
  return $ PublicGame {
        nonce = Saltine.encode n
      , playerHand = getHand playerID (KoiKoi.players game)
      , private = secretbox encrypt n $ toJSON private
      , public
      , publicSignature = signDetached (Keys.secret sign) $ toJSON public
    }
  where
    public = publicState game
    private = privateState game

toJSON :: ToJSON a => a -> ByteString
toJSON = toStrict . encode

gameOf :: PublicState -> PrivateState -> Game
gameOf public private = KoiKoi.Game {
        KoiKoi.mode = mode public
      , KoiKoi.scores = scores public
      , KoiKoi.month = month public
      , KoiKoi.nextPlayer = nextPlayer public
      , KoiKoi.players = Player.Players $
          mapWithKey (privatePlayer $ players public) (hands private)
      , KoiKoi.playing = playing public
      , KoiKoi.winning = winning public
      , KoiKoi.oyake = winning public
      , KoiKoi.deck = deck private
      , KoiKoi.river = river public
      , KoiKoi.step = step public
      , KoiKoi.trick = trick public
      , KoiKoi.rounds = rounds public
    }

importGame :: PublicGame -> App.T (Either String Game)
importGame PublicGame {nonce, private, public, publicSignature} = do
  Keys.T {encrypt, sign} <- App.get Server.keys
  if signVerifyDetached (Keys.public sign) publicSignature $ toJSON public
  then return $ do
    n <- Saltine.decode nonce `orDie` "Could not decode nonce"
    decrypted <- secretboxOpen encrypt n private
                  `orDie` "Could not decrypt private state"
    gameOf public <$> eitherDecode' (fromStrict decrypted)
  else return $ Left "The game state has been tampered with"
  where
    orDie :: Maybe a -> String -> Either String a
    orDie m errorMessage = maybe (Left errorMessage) Right m

play :: PlayerID -> KoiKoi.Move -> PublicGame -> App.T (Either String (Game, [KoiKoi.Action]))
play playerID move publicGame
  | playing (public publicGame) == playerID = do
      imported <- importGame publicGame
      case imported of
        Left errorMessage -> return $ Left errorMessage
        Right game -> lift . runExceptT . runWriterT $ KoiKoi.play move game
  | otherwise = return $ Left "Not your turn"