{-# LANGUAGE CPP #-}

module Language.Haskell.GhcMod.CaseSplit (
    splits
  ) where

import Data.List (find, intercalate)
import Data.Maybe (isJust)
import qualified Data.Text as T
import qualified Data.Text.IO as T (readFile)
import qualified DataCon as Ty
import Exception (ghandle, SomeException(..))
import GHC (GhcMonad, LPat, Id, ParsedModule(..), TypecheckedModule(..), DynFlags, SrcSpan, Type, GenLocated(L))
import qualified GHC as G
import Language.Haskell.GhcMod.Convert
import qualified Language.Haskell.GhcMod.Gap as Gap
import Language.Haskell.GhcMod.Monad
import Language.Haskell.GhcMod.SrcUtils
import Outputable (PprStyle)
import qualified TyCon as Ty
import qualified Type as Ty

----------------------------------------------------------------
-- CASE SPLITTING
----------------------------------------------------------------

data SplitInfo = SplitInfo G.Name SrcSpan (SrcSpan, Type) [SrcSpan]
               | TySplitInfo G.Name SrcSpan (SrcSpan, Ty.Kind)
data SplitToTextInfo = SplitToTextInfo { sVarName     :: String
                                       , sBindingSpan :: SrcSpan
                                       , sVarSpan     :: SrcSpan
                                       , sTycons      :: [String]
                                       }

-- | Splitting a variable in a equation.
splits :: IOish m
       => FilePath     -- ^ A target file.
       -> Int          -- ^ Line number.
       -> Int          -- ^ Column number.
       -> GhcModT m String
splits file lineNo colNo = ghandle handler body
  where
    body = inModuleContext file $ \dflag style -> do
        opt <- options
        modSum <- Gap.fileModSummary file
        whenFound' opt (getSrcSpanTypeForSplit modSum lineNo colNo) $ \x -> case x of
          (SplitInfo varName bndLoc (varLoc,varT) _matches) -> do
             let varName' = showName dflag style varName  -- Convert name to string
             text <- genCaseSplitTextFile file (SplitToTextInfo varName' bndLoc varLoc $
                                                getTyCons dflag style varName varT)
             return (fourInts bndLoc, text)
          (TySplitInfo varName bndLoc (varLoc,varT)) -> do
             let varName' = showName dflag style varName  -- Convert name to string
             text <- genCaseSplitTextFile file (SplitToTextInfo varName' bndLoc varLoc $
                                                getTyCons dflag style varName varT)
             return (fourInts bndLoc, text)
    handler (SomeException _) = emptyResult =<< options

----------------------------------------------------------------
-- a. Code for getting the information of the variable

getSrcSpanTypeForSplit :: GhcMonad m => G.ModSummary -> Int -> Int -> m (Maybe SplitInfo)
getSrcSpanTypeForSplit modSum lineNo colNo = do
  fn <- getSrcSpanTypeForFnSplit modSum lineNo colNo
  if isJust fn
     then return fn
     else getSrcSpanTypeForTypeSplit modSum lineNo colNo

-- Information for a function case split
getSrcSpanTypeForFnSplit :: GhcMonad m => G.ModSummary -> Int -> Int -> m (Maybe SplitInfo)
getSrcSpanTypeForFnSplit modSum lineNo colNo = do
    p@ParsedModule{pm_parsed_source = _pms} <- G.parseModule modSum
    tcm@TypecheckedModule{tm_typechecked_source = tcs} <- G.typecheckModule p
    let varPat  = find isPatternVar $ listifySpans tcs (lineNo, colNo) :: Maybe (LPat Id)
        match:_ = listifySpans tcs (lineNo, colNo) :: [Gap.GLMatchI]
    case varPat of
      Nothing  -> return Nothing
      Just varPat' -> do
        varT <- Gap.getType tcm varPat'  -- Finally we get the type of the var
        case varT of
          Just varT' ->
            let (L matchL (G.Match _ _ (G.GRHSs rhsLs _))) = match
            in return $ Just (SplitInfo (getPatternVarName varPat') matchL varT' (map G.getLoc rhsLs) )
          _ -> return Nothing

isPatternVar :: LPat Id -> Bool
isPatternVar (L _ (G.VarPat _)) = True
isPatternVar _                  = False

getPatternVarName :: LPat Id -> G.Name
getPatternVarName (L _ (G.VarPat vName)) = G.getName vName
getPatternVarName _                      = error "This should never happened"

-- TODO: Information for a type family case split
getSrcSpanTypeForTypeSplit :: GhcMonad m => G.ModSummary -> Int -> Int -> m (Maybe SplitInfo)
getSrcSpanTypeForTypeSplit _modSum _lineNo _colNo = return Nothing

----------------------------------------------------------------
-- b. Code for getting the possible constructors

getTyCons :: DynFlags -> PprStyle -> G.Name -> G.Type ->  [String]
getTyCons dflag style name ty | Just (tyCon, _) <- Ty.splitTyConApp_maybe ty =
  let name' = showName dflag style name  -- Convert name to string
  in getTyCon dflag style name' tyCon
getTyCons dflag style name _ = [showName dflag style name]

-- Write cases for one type
getTyCon :: DynFlags -> PprStyle -> String -> Ty.TyCon -> [String]
-- 1. Non-matcheable type constructors
getTyCon _ _ name tyCon | isNotMatcheableTyCon tyCon = [name]
-- 2. Special cases
-- 2.1. Tuples
getTyCon _ _ name tyCon | Ty.isTupleTyCon tyCon =
  let [uniqueDataCon] = Ty.tyConDataCons tyCon
      tupleArity = Ty.dataConSourceArity uniqueDataCon
      -- Deal with both boxed and unboxed tuples
      isUnboxed = Ty.isUnboxedTupleTyCon tyCon
      startSign = if isUnboxed then "(#" else "("
      endSign   = if isUnboxed then "#)" else ")"
  in [ startSign ++ intercalate "," (map (\n -> name ++ show n) [1 .. tupleArity]) ++ endSign ]
-- 3. General case
getTyCon dflag style name tyCon = map (getDataCon dflag style name) (Ty.tyConDataCons tyCon)

-- These type constructors should not be matched against
isNotMatcheableTyCon :: Ty.TyCon -> Bool
isNotMatcheableTyCon ty = Ty.isPrimTyCon ty  -- Primitive types, such as Int#
                       || Ty.isFunTyCon ty   -- Function types

-- Write case for one constructor
getDataCon :: DynFlags -> PprStyle -> String -> Ty.DataCon -> String
-- 1. Infix constructors
getDataCon dflag style vName dcon | Ty.dataConIsInfix dcon =
  let dName  = showName dflag style $ Ty.dataConName dcon
  in case Ty.dataConSourceArity dcon of
       0 -> dName
       1 -> vName ++ dName
       n -> if dName == ":" -- Special case for lists
            then vName ++ ":" ++ vName ++ "s"
            else newVar vName 1 ++ " " ++ dName ++ " " ++ newVars vName 2 (n-1)
-- 2. Non-record, non-infix syntax
getDataCon dflag style vName dcon | [] <- Ty.dataConFieldLabels dcon =
  let dName  = showName dflag style $ Ty.dataConName dcon
  in if last dName == '#'  -- Special case for I#, C# and so on
     then vName
     else case Ty.dataConSourceArity dcon of
            0 -> dName
            _ -> dName ++ " " ++ newVarsSpecialSingleton vName 1 (Ty.dataConSourceArity dcon)
-- 3. Records
getDataCon dflag style vName dcon =
  let dName = showName dflag style $ Ty.dataConName dcon
      flds  = Ty.dataConFieldLabels dcon
  in dName ++ " { " ++ showFieldNames dflag style vName flds ++ " }"

-- Create a new variable by adjoining a number
newVar :: String -> Int -> String
newVar v n = v ++ show n

-- Create a list of variables which start with the same prefix
newVars :: String -> Int -> Int -> String
newVars _ _ 0 = ""
newVars v s 1 = newVar v s
newVars v s m = newVar v s ++ " " ++ newVars v (s+1) (m-1)

-- Create a list of variables which start with the same prefix
-- Special case for a single variable, in which case no number is adjoint
newVarsSpecialSingleton :: String -> Int -> Int -> String
newVarsSpecialSingleton v _     1 = v
newVarsSpecialSingleton v start n = newVars v start n

showFieldNames :: DynFlags -> PprStyle -> String -> [G.Name] -> String
showFieldNames _     _     _ []      = "" -- This should never happen
showFieldNames dflag style v (x:xs) = let fName = showName dflag style x
                                          fAcc  = fName ++ " = " ++ v ++ "_" ++ fName
                                       in case xs of
                                            [] -> fAcc
                                            _  -> fAcc ++ ", " ++ showFieldNames dflag style v xs

----------------------------------------------------------------
-- c. Code for performing the case splitting

genCaseSplitTextFile :: GhcMonad m => FilePath -> SplitToTextInfo -> m String
genCaseSplitTextFile file info = liftIO $ do
  text <- T.readFile file
  return $ getCaseSplitText (T.lines text) info

getCaseSplitText :: [T.Text] -> SplitToTextInfo -> String
getCaseSplitText text (SplitToTextInfo { sVarName = sVN, sBindingSpan = sBS
                                       , sVarSpan = sVS, sTycons = sT })  =
  let bindingText = getBindingText text sBS
      difference  = srcSpanDifference sBS sVS
      replaced    = concatMap (replaceVarWithTyCon bindingText difference sVN) sT
   in T.unpack $ T.intercalate (T.pack "\n") replaced

getBindingText :: [T.Text] -> SrcSpan -> [T.Text]
getBindingText text srcSpan =
  let Just (sl,sc,el,ec) = Gap.getSrcSpan srcSpan
      lines_ = drop (sl - 1) $ take el text
   in if sl == el
      then -- only one line
           [T.drop (sc - 1) $ T.take ec $ head lines_]
      else -- several lines
            let (first,rest,last_) = (head lines_, tail $ init lines_, last lines_)
             in T.drop (sc - 1) first : rest ++ [T.take ec last_]

srcSpanDifference :: SrcSpan -> SrcSpan -> (Int,Int,Int,Int)
srcSpanDifference b v =
  let Just (bsl,bsc,_   ,_)  = Gap.getSrcSpan b
      Just (vsl,vsc,vel,vec) = Gap.getSrcSpan v
   in (vsl - bsl, vsc - bsc, vel - bsl, vec - bsc) -- assume variable in one line

replaceVarWithTyCon :: [T.Text] -> (Int,Int,Int,Int) -> String -> String -> [T.Text]
replaceVarWithTyCon text (vsl,vsc,_,vec) varname tycon =
  let tycon'      = if ' ' `elem` tycon || ':' `elem` tycon then "(" ++ tycon ++ ")" else tycon
      lengthDiff  = length tycon' - length varname
      tycon''     = T.pack $ if lengthDiff < 0 then tycon' ++ replicate (-lengthDiff) ' ' else tycon'
      spacesToAdd = if lengthDiff < 0 then 0 else lengthDiff
   in zipWith (\n line -> if n < vsl
                          then line  -- before variable starts
                          else if n == vsl
                               then T.take vsc line `T.append` tycon'' `T.append` T.drop vec line
                               else T.replicate spacesToAdd (T.pack " ") `T.append` line)
              [0 ..] text