{-# LANGUAGE GHC2024 #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE QuasiQuotes #-}
-- base
import GHC.TypeLits (SNat, KnownNat (natSing), natVal, withSomeSNat, fromSNat)
-- template-haskell
import qualified Language.Haskell.TH          as TH

class KnownNat n => ValidUINTn n

data UINTn where
  UINTn :: ValidUINTn n => SNat n -> UINTn

flip foldMap [1..32] $ \i -> [d| instance ValidUINTn $(TH.litT (TH.numTyLit i)) |]

instance Show UINTn where
  show (UINTn sn) = "UINT" <> show (natVal sn * 8)

getValidUINTn :: Integer -> Maybe UINTn
getValidUINTn x = withSomeSNat x $ \maybeSn -> maybeSn >>=
  \sn -> let n = fromSNat sn
         in $(TH.caseE
              (TH.varE 'n)
              (map
                (\i ->
                  TH.match
                    (TH.litP (TH.integerL i))
                    (TH.normalB (
                      TH.conE 'Just
                      `TH.appE`
                      ((TH.conE 'UINTn)
                        `TH.appE`
                        (TH.varE 'natSing
                         `TH.appTypeE`
                         TH.litT (TH.numTyLit i)))))
                    []
                )
                [1..32]
              ++
              [ TH.match TH.wildP (TH.normalB (TH.conE 'Nothing)) [] ]
              )
            )

main = do
  print $ UINTn (natSing @2)
  print $ getValidUINTn 4
  print $ getValidUINTn 32
  print $ getValidUINTn 33