{-# LANGUAGE ImportQualifiedPost #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE TemplateHaskellQuotes #-}
module Data.Array.Nested.Trace.TH where

import Control.Monad (zipWithM)
import Data.List (foldl', intersperse)
import Data.Maybe (isJust)
import Language.Haskell.TH hiding (cxt)

import Debug.Trace qualified as Debug

import Data.Array.Nested


splitFunTy :: Type -> ([TyVarBndr Specificity], Cxt, [Type], Type)
splitFunTy = \case
  ArrowT `AppT` t1 `AppT` t2 ->
    let (vars, cx, args, ret) = splitFunTy t2
    in (vars, cx, t1 : args, ret)
  ForallT vs cx' t ->
    let (vars, cx, args, ret) = splitFunTy t
    in (vars ++ vs, cx ++ cx', args, ret)
  t -> ([], [], [], t)

data Arg = RRanked Type Arg
         | RShaped Type Arg
         | RMixed Type Arg
         | RShowable Type
         | ROther Type
  deriving (Show)

-- TODO: always returns Just
recognise :: Type -> Maybe Arg
recognise (ConT name `AppT` sht `AppT` ty)
  | name == ''Ranked = RRanked sht <$> recognise ty
  | name == ''Shaped = RShaped sht <$> recognise ty
  | name == ''Mixed = RMixed sht <$> recognise ty
recognise ty@(ConT name `AppT` _)
  | name `elem` [''IShR, ''IIxR, ''ShS, ''IIxS, ''SNat] =
      Just (RShowable ty)
recognise _ = Nothing

realise :: Arg -> Type
realise (RRanked sht ty) = ConT ''Ranked `AppT` sht `AppT` realise ty
realise (RShaped sht ty) = ConT ''Shaped `AppT` sht `AppT` realise ty
realise (RMixed sht ty) = ConT ''Mixed `AppT` sht `AppT` realise ty
realise (RShowable ty) = ty
realise (ROther ty) = ty

mkShow :: Arg -> Cxt
mkShow (RRanked _ ty) = mkShowElt ty
mkShow (RShaped _ ty) = mkShowElt ty
mkShow (RMixed sht ty) = [ConT ''Show `AppT` realise (RMixed sht ty)]
mkShow (RShowable _) = []
mkShow (ROther ty) = [ConT ''Show `AppT` ty]

mkShowElt :: Arg -> Cxt
mkShowElt (RRanked _ ty) = mkShowElt ty
mkShowElt (RShaped _ ty) = mkShowElt ty
mkShowElt (RMixed sht ty) = [ConT ''Show `AppT` realise (RMixed sht ty), ConT ''Elt `AppT` realise (RMixed sht ty)]
mkShowElt (RShowable _ty) = []  -- [ConT ''Elt `AppT` ty]
mkShowElt (ROther ty) = [ConT ''Show `AppT` ty, ConT ''Elt `AppT` ty]

convertType :: Type -> Q (Type, [Bool], Bool)
convertType typ =
  let (tybndrs, cxt, args, ret) = splitFunTy typ
      argrels = map recognise args
      retrel = recognise ret
  in return
      (ForallT tybndrs
               (cxt ++ [constr
                       | Just rel <- retrel : argrels
                       , constr <- mkShow rel])
               (foldr (\a b -> ArrowT `AppT` a `AppT` b) ret args)
      ,map isJust argrels
      ,isJust retrel)

convertFun :: Name -> Q [Dec]
convertFun funname = do
  defname <- newName (nameBase funname)
  (convty, argarrs, retarr) <- reifyType funname >>= convertType
  names <- zipWithM (\b i -> newName ((if b then "t" else "x") ++ show i)) argarrs [1::Int ..]
  resname <- newName "res"
  let tracenames = map fst (filter snd (zip (names ++ [resname]) (argarrs ++ [retarr])))
  let ex = LetE [ValD (VarP resname)
                      (NormalB (foldl' AppE (VarE funname) (map VarE names)))
                      []]
                (VarE 'Debug.trace
                  `AppE` (VarE 'concat `AppE` ListE
                            ([LitE (StringL ("oxtrace: " ++ nameBase funname ++ " ["))] ++
                             intersperse (LitE (StringL ", "))
                                         (map (\n -> VarE 'show `AppE` VarE n) tracenames) ++
                             [LitE (StringL "]")]))
                  `AppE` VarE resname)
  return
    [SigD defname convty
    ,FunD defname [Clause (map VarP names) (NormalB ex) []]]