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module StylishHaskell.Step.Imports
    ( Align (..)
    , step
    ) where


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import           Control.Arrow                   ((&&&))
import           Data.Char                       (isAlpha, toLower)
import           Data.List                       (sortBy)
import           Data.Maybe                      (isJust, maybeToList)
import           Data.Ord                        (comparing)
import qualified Language.Haskell.Exts.Annotated as H


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import           StylishHaskell.Block
import           StylishHaskell.Editor
import           StylishHaskell.Step
import           StylishHaskell.Util


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data Align
    = Global
    | Group
    | None
    deriving (Eq, Show)


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imports :: H.Module l -> [H.ImportDecl l]
imports (H.Module _ _ _ is _) = is
imports _                     = []


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importName :: H.ImportDecl l -> String
importName i = let (H.ModuleName _ n) = H.importModule i in n


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longestImport :: [H.ImportDecl l] -> Int
longestImport = maximum . map (length . importName)


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-- | Groups adjacent imports into larger import blocks
groupAdjacent :: [H.ImportDecl LineBlock]
              -> [(LineBlock, [H.ImportDecl LineBlock])]
groupAdjacent = foldr go []
  where
    -- This code is ugly and not optimal, and no fucks were given.
    go imp is = case break (adjacent b1 . fst) is of
        (_, [])                 -> (b1, [imp]) : is
        (xs, ((b2, imps) : ys)) -> (merge b1 b2, imp : imps) : (xs ++ ys)
      where
        b1 = H.ann imp


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-- | Compare imports for ordering
compareImports :: H.ImportDecl l -> H.ImportDecl l -> Ordering
compareImports = comparing (map toLower . importName &&& H.importQualified)


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-- | The implementation is a bit hacky to get proper sorting for input specs:
-- constructors first, followed by functions, and then operators.
compareImportSpecs :: H.ImportSpec l -> H.ImportSpec l -> Ordering
compareImportSpecs = comparing key
  where
    key :: H.ImportSpec l -> (Int, Int, String)
    key (H.IVar _ x)         = let n = nameToString x in (1, operator n, n)
    key (H.IAbs _ x)         = (0, 0, nameToString x)
    key (H.IThingAll _ x)    = (0, 0, nameToString x)
    key (H.IThingWith _ x _) = (0, 0, nameToString x)

    operator []      = 0  -- But this should not happen
    operator (x : _) = if isAlpha x then 0 else 1


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-- | Sort the input spec list inside an 'H.ImportDecl'
sortImportSpecs :: H.ImportDecl l -> H.ImportDecl l
sortImportSpecs imp = imp {H.importSpecs = fmap sort $ H.importSpecs imp}
  where
    sort (H.ImportSpecList l h specs) = H.ImportSpecList l h $
        sortBy compareImportSpecs specs


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prettyImport :: Bool -> Bool -> Int -> H.ImportDecl l -> String
prettyImport padQualified padName longest imp = unwords $ concat
    [ ["import"]
    , qualified
    , [(if hasExtras && padName then padRight longest else id) (importName imp)]
    , ["as " ++ as | H.ModuleName _ as <- maybeToList $ H.importAs imp]
    , [H.prettyPrint specs | specs <- maybeToList $ H.importSpecs imp]
    ]
  where
    hasExtras = isJust (H.importAs imp) || isJust (H.importSpecs imp)

    qualified
        | H.importQualified imp = ["qualified"]
        | padQualified          = ["         "]
        | otherwise             = []


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prettyImportGroup :: Align -> Int -> [H.ImportDecl LineBlock] -> Lines
prettyImportGroup align longest imps =
    map (prettyImport padQual padName longest') $ sortBy compareImports imps
  where
    longest' = case align of
        Group -> longestImport imps
        _     -> longest

    padName = align /= None

    padQual = case align of
        Global -> True
        Group  -> any H.importQualified imps
        None   -> False


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step :: Align -> Step
step = makeStep "Imports" . step'


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step' :: Align -> Lines -> Module -> Lines
step' align ls (module', _) = flip applyChanges ls
    [ change block (prettyImportGroup align longest importGroup)
    | (block, importGroup) <- groups
    ]
  where
    imps    = map sortImportSpecs $ imports $ fmap linesFromSrcSpan module'
    longest = longestImport imps
    groups  = groupAdjacent imps