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module Language.Haskell.Stylish.Step.LanguagePragmas
    ( Style (..)
    , step
      -- * Utilities
    , addLanguagePragma
    ) where


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import qualified Data.Set                        as S
import qualified Language.Haskell.Exts           as H


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import           Language.Haskell.Stylish.Block
import           Language.Haskell.Stylish.Editor
import           Language.Haskell.Stylish.Step
import           Language.Haskell.Stylish.Util


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data Style
    = Vertical
    | Compact
    | CompactLine
    deriving (Eq, Show)


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pragmas :: H.Module l -> [(l, [String])]
pragmas (H.Module _ _ ps _ _) =
    [(l, map nameToString names) | H.LanguagePragma l names <- ps]
pragmas _                     = []


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-- | The start of the first block
firstLocation :: [(Block a, [String])] -> Int
firstLocation = minimum . map (blockStart . fst)


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verticalPragmas :: String -> Int -> Bool -> [String] -> Lines
verticalPragmas lg longest align pragmas' =
    [ "{-# " ++ lg ++ " " ++ pad pragma ++ " #-}"
    | pragma <- pragmas'
    ]
  where
    pad
      | align = padRight longest
      | otherwise = id


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compactPragmas :: String -> Maybe Int -> [String] -> Lines
compactPragmas lg columns pragmas' = wrapMaybe columns ("{-# " ++ lg) 13 $
    map (++ ",") (init pragmas') ++ [last pragmas' ++ " #-}"]


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compactLinePragmas :: String -> Maybe Int -> Bool -> [String] -> Lines
compactLinePragmas _  _ _ [] = []
compactLinePragmas lg columns align pragmas' = map (wrapLanguage . pad) prags
  where
    wrapLanguage ps = "{-# " ++ lg ++ ps ++  " #-}"
    maxWidth = fmap (\c -> c - 16) columns
    longest  = maximum $ map length prags
    pad
      | align = padRight longest
      | otherwise = id
    prags = map truncateComma $ wrapMaybe maxWidth "" 1 $
      map (++ ",") (init pragmas') ++ [last pragmas']


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truncateComma :: String -> String
truncateComma ""     = ""
truncateComma xs
    | last xs == ',' = init xs
    | otherwise      = xs


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prettyPragmas :: String -> Maybe Int -> Int -> Bool -> Style -> [String] -> Lines
prettyPragmas lp _    longest align Vertical    = verticalPragmas lp longest align
prettyPragmas lp cols _       _     Compact     = compactPragmas lp cols
prettyPragmas lp cols _       align CompactLine = compactLinePragmas lp cols align


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-- | Filter redundant (and duplicate) pragmas out of the groups. As a side
-- effect, we also sort the pragmas in their group...
filterRedundant :: (String -> Bool)
                -> [(l, [String])]
                -> [(l, [String])]
filterRedundant isRedundant' = snd . foldr filterRedundant' (S.empty, [])
  where
    filterRedundant' (l, xs) (known, zs)
        | S.null xs' = (known', zs)
        | otherwise  = (known', (l, S.toAscList xs') : zs)
      where
        fxs    = filter (not . isRedundant') xs
        xs'    = S.fromList fxs `S.difference` known
        known' = xs' `S.union` known

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step :: Maybe Int -> Style -> Bool -> Bool -> String -> Step
step = ((((makeStep "LanguagePragmas" .) .) .) .) . step'


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step' :: Maybe Int -> Style -> Bool -> Bool -> String -> Lines -> Module -> Lines
step' columns style align removeRedundant lngPrefix ls (module', _)
    | null pragmas' = ls
    | otherwise     = applyChanges changes ls
  where
    isRedundant'
        | removeRedundant = isRedundant module'
        | otherwise       = const False
    pragmas' = pragmas $ fmap linesFromSrcSpan module'
    longest  = maximum $ map length $ snd =<< pragmas'
    groups   = [(b, concat pgs) | (b, pgs) <- groupAdjacent pragmas']
    changes  =
        [ change b (const $ prettyPragmas lngPrefix columns longest align style pg)
        | (b, pg) <- filterRedundant isRedundant' groups
        ]


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-- | Add a LANGUAGE pragma to a module if it is not present already.
addLanguagePragma :: String -> String -> H.Module H.SrcSpanInfo -> [Change String]
addLanguagePragma lg prag modu
    | prag `elem` present = []
    | otherwise           = [insert line ["{-# " ++ lg ++ " " ++ prag ++ " #-}"]]
  where
    pragmas' = pragmas (fmap linesFromSrcSpan modu)
    present  = concatMap snd pragmas'
    line     = if null pragmas' then 1 else firstLocation pragmas'


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-- | Check if a language pragma is redundant. We can't do this for all pragmas,
-- but we do a best effort.
isRedundant :: H.Module H.SrcSpanInfo -> String -> Bool
isRedundant m "ViewPatterns" = isRedundantViewPatterns m
isRedundant m "BangPatterns" = isRedundantBangPatterns m
isRedundant _ _              = False


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-- | Check if the ViewPatterns language pragma is redundant.
isRedundantViewPatterns :: H.Module H.SrcSpanInfo -> Bool
isRedundantViewPatterns m = null
    [() | H.PViewPat {} <- everything m :: [H.Pat H.SrcSpanInfo]]


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-- | Check if the BangPatterns language pragma is redundant.
isRedundantBangPatterns :: H.Module H.SrcSpanInfo -> Bool
isRedundantBangPatterns m = null
    [() | H.PBangPat _ _ <- everything m :: [H.Pat H.SrcSpanInfo]]