{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE ImportQualifiedPost #-}
#!/usr/bin/env cabal
{- cabal:
build-depends: base
             , text
             , kdl-hs
-}

import KDL
import KDL.Decoder.Internal.Decoder
import Control.Applicative
import Data.Text
import Data.Text qualified as T
import Data.Text.IO qualified as T

newtype Var = Var Text
  deriving stock (Eq,Ord, Show)

myNodeDecoder :: DecodeArrow NodeList () (Either Var Text)
myNodeDecoder =
  KDL.nodeWith "node" $
    (Right <$> KDL.argWith' ["text"] KDL.text)
      <|> (Left <$> KDL.argWith' ["var"] (Var <$> KDL.text))

main :: IO ()
main = do
  let input1 = "node (var)ref"
  let input2 = "node value"
  let decoder = KDL.document myNodeDecoder
  T.putStrLn $ processResult $ KDL.decodeWith decoder input1
  T.putStrLn $ processResult $ KDL.decodeWith decoder input2

processResult :: Show a => Either DecodeError a -> Text
processResult (Left err) = renderDecodeError err
processResult (Right value) = T.show value