module HBS2.OrDie
  ( module HBS2.OrDie
  ) where

import Data.Kind
import Control.Monad.IO.Class
import System.Exit
import Prettyprinter
import UnliftIO

class OrDie m a where
  type family OrDieResult a :: Type
  orDie :: m a -> String -> m (OrDieResult a)

orDieM :: (Monad m, OrDie m a) => a -> String -> m (OrDieResult a)
orDieM a msg = pure a `orDie` msg

instance MonadIO m => OrDie m (Maybe a) where
  type instance OrDieResult (Maybe a) = a
  orDie mv err = mv >>= \case
      Nothing -> liftIO $ die err
      Just x  -> pure x

instance MonadIO m => OrDie m (Either a b) where
  type instance OrDieResult (Either a b) = b
  orDie mv err = mv >>= \case
      Left{} -> liftIO $ die err
      Right x  -> pure x

instance MonadIO m => OrDie m ExitCode where
  type instance OrDieResult ExitCode = ()
  orDie mv err = mv >>= \case
    ExitSuccess   -> pure ()
    ExitFailure{} -> liftIO $ die err


-- TODO: move-to-library
class OrThrow a  where
  type family OrThrowResult a :: Type
  orThrow :: forall e m  . (MonadIO m, Exception e) =>  e -> a -> m (OrThrowResult a)

instance OrThrow (Maybe a) where
  type instance OrThrowResult (Maybe a) = a
  orThrow e a = case a of
    Nothing -> throwIO e
    Just x  -> pure x


instance OrThrow (Either b a) where
  type instance OrThrowResult (Either b a) = a
  orThrow e a = case a of
    Left{}  -> throwIO e
    Right x -> pure x

orThrowUser :: (OrThrow a1, MonadIO m)
            => Doc ann
            -> a1
            -> m (OrThrowResult a1)

orThrowUser p = orThrow (userError (show p))