{-# LANGUAGE ViewPatterns, PatternGuards #-}

{-
    Find and match:

<TEST>
yes = 1:2:[] -- [1,2]
yes = ['h','e','l','l','o'] -- "hello"

-- [a]++b -> a : b, but only if not in a chain of ++'s
yes = [x] ++ xs -- x : xs
yes = "x" ++ xs -- 'x' : xs
no = [x] ++ xs ++ ys
no = xs ++ [x] ++ ys
yes = [if a then b else c] ++ xs -- (if a then b else c) : xs
yes = [1] : [2] : [3] : [4] : [5] : [] -- [[1], [2], [3], [4], [5]]
yes = if x == e then l2 ++ xs else [x] ++ check_elem xs -- x : check_elem xs
data Yes = Yes (Maybe [Char]) -- (Maybe String)
yes = y :: [Char] -> a -- String -> a
</TEST>
-}


module Hint.List where

import HSE.All
import Type


listHint :: DeclHint
listHint _ = listDecl

listDecl :: Decl -> [Idea]
listDecl x = concatMap (listExp False) (children0Exp nullSrcLoc x) ++
             concatMap (stringType (declSrcLoc x)) (childrenBi x)

-- boolean = are you in a ++ chain
listExp :: Bool -> (SrcLoc,Exp) -> [Idea]
listExp b (loc,x) =
        if null res then concatMap (listExp $ isAppend x) $ children1Exp loc x else [head res]
    where
        res = [warn name loc x x2 | (name,f) <- checks, Just x2 <- [f b x]]


isAppend (view -> App2 op _ _) = op ~= "++"
isAppend _ = False


checks = let (*) = (,) in
         ["Use string literal" * useString
         ,"Use list literal" * useList
         ,"Use :" * useCons
         ]


useString b (List xs) | xs /= [] && all isChar xs = Just $ Lit $ String $ map fromChar xs
useString b _ = Nothing

useList b = fmap List . f True
    where
        f first x | x ~= "[]" = if first then Nothing else Just []
        f first (view -> App2 c a b) | c ~= ":" = fmap (a:) $ f False b
        f first _ = Nothing

useCons False (view -> App2 op x y) | op ~= "++", Just x2 <- f x, not $ isAppend y =
        Just $ InfixApp x2 (QConOp list_cons_name) y
    where
        f (Lit (String [x])) = Just $ Lit $ Char x
        f (List [x]) = Just $ paren x
        f _ = Nothing
useCons _ _ = Nothing



typeListChar = TyApp (TyCon (Special ListCon)) (TyCon (UnQual (Ident "Char")))
typeString = TyCon (UnQual (Ident "String"))


stringType :: SrcLoc -> Type -> [Idea]
stringType loc x = [warn "Use String" loc x (transform f x) | typeListChar `elem` universe x]
    where f x = if x == typeListChar then typeString else x