{-# OPTIONS_GHC -W #-}

{-| This module contains checks to be run *after* type inference has completed
successfully. At that point we still need to do occurs checks and ensure that
`main` has an acceptable type.
-}
module Type.ExtraChecks (mainType, occurs, portTypes) where

import Control.Applicative ((<$>),(<*>))
import Control.Monad.State
import qualified Data.Map as Map
import qualified Data.Traversable as Traverse
import qualified Data.UnionFind.IO as UF
import Text.PrettyPrint as P

import qualified AST.Annotation as A
import qualified AST.Expression.General as E
import qualified AST.Expression.Canonical as Canonical
import qualified AST.Helpers as Help
import qualified AST.PrettyPrint as PP
import qualified AST.Type as ST
import qualified AST.Variable as V
import qualified Transform.Expression as Expr
import qualified Type.Type as TT
import qualified Type.State as TS
import qualified Type.Alias as Alias

throw err = Left [ P.vcat err ]

mainType :: Alias.Rules -> TS.Env -> IO (Either [P.Doc] (Map.Map String ST.CanonicalType))
mainType rules env = mainCheck rules <$> Traverse.traverse TT.toSrcType env
  where
    mainCheck :: Alias.Rules -> Map.Map String ST.CanonicalType -> Either [P.Doc] (Map.Map String ST.CanonicalType)
    mainCheck rules env =
      case Map.lookup "main" env of
        Nothing -> Right env
        Just mainType
            | tipe `elem` acceptable -> Right env
            | otherwise              -> throw err
            where
              acceptable = [ "Graphics.Element.Element"
                           , "Signal.Signal Graphics.Element.Element" ]

              tipe = PP.renderPretty $ Alias.canonicalRealias (fst rules) mainType
              err = [ P.text "Type Error: 'main' must have type Element or (Signal Element)."
                    , P.text "Instead 'main' has type:\n"
                    , P.nest 4 . PP.pretty $ Alias.realias rules mainType
                    , P.text " " ]

data Direction = In | Out

portTypes :: Alias.Rules -> Canonical.Expr -> Either [P.Doc] ()
portTypes rules expr =
  const () <$> Expr.checkPorts (check In) (check Out) expr
  where
    check = isValid True False False
    isValid isTopLevel seenFunc seenSignal direction name tipe =
        case tipe of
          ST.Data (V.Canonical (V.Module "Signal") "Signal") [t] ->
              handleSignal t

          ST.Data (V.Canonical (V.Module "Maybe") "Maybe") [t] ->
              valid t

          ST.Data (V.Canonical (V.Module "Json") "Value") [] ->
              return ()

          ST.Data (V.Canonical V.BuiltIn ctor) ts
              | ctor `elem` primitives || Help.isTuple ctor -> mapM_ valid ts
              where
                primitives = ["Int","Float","String","Bool","_List"]
                    
          ST.Data _ _ -> err' True "an unsupported type"

          ST.Var _ -> err "free type variables"

          ST.Lambda _ _ ->
              case direction of
                In -> err "functions"
                Out | seenFunc   -> err "higher-order functions"
                    | seenSignal -> err "signals that contain functions"
                    | otherwise  ->
                        forM_ (ST.collectLambdas tipe)
                              (isValid' True seenSignal direction name)

          ST.Record _ (Just _) -> err "extended records with free type variables"

          ST.Record fields Nothing ->
              mapM_ (\(k,v) -> (,) k <$> valid v) fields

        where
          isValid' = isValid False
          valid = isValid' seenFunc seenSignal direction name

          handleSignal t
              | seenFunc   = err "functions that involve signals"
              | seenSignal = err "signals-of-signals"
              | isTopLevel = isValid' seenFunc True direction name t
              | otherwise  = err "a signal within a data stucture"

          dir inMsg outMsg = case direction of { In -> inMsg ; Out -> outMsg }
          txt = P.text . concat

          err = err' False
          err' couldBeAlias kind =
              throw $
              [ txt [ "Type Error: the value ", dir "coming in" "sent out"
                    , " through port '", name, "' is invalid." ]
              , txt [ "It contains ", kind, ":\n" ]
              , (P.nest 4 . PP.pretty $ Alias.realias rules tipe) <> P.text "\n"
              , txt [ "Acceptable values for ", dir "incoming" "outgoing", " ports include:" ]
              , txt [ "    Ints, Floats, Bools, Strings, Maybes, Lists, Tuples," ]
              , txt [ "    Json.Values, ", dir "" "first-order functions, ", "and concrete records." ]
              ] ++ if couldBeAlias then aliasWarning else []

          aliasWarning =
              [ txt [ "\nType aliases are not expanded for this check (yet) so you need to do that" ]
              , txt [ "manually for now (e.g. {x:Int,y:Int} instead of a type alias of that type)." ]
              ]

occurs :: (String, TT.Variable) -> StateT TS.SolverState IO ()
occurs (name, variable) =
  do vars <- liftIO $ infiniteVars [] variable
     case vars of
       [] -> return ()
       var:_ -> do
         desc <- liftIO $ UF.descriptor var
         case TT.structure desc of
           Nothing ->
               modify $ \state -> state { TS.sErrors = fallback : TS.sErrors state }
           Just _ ->
               do liftIO $ UF.setDescriptor var (desc { TT.structure = Nothing })
                  var' <- liftIO $ UF.fresh desc
                  TS.addError (A.None (P.text name)) (Just msg) var var'
  where
    msg = "Infinite types are not allowed"
    fallback _ = return $ P.text msg

    infiniteVars :: [TT.Variable] -> TT.Variable -> IO [TT.Variable]
    infiniteVars seen var = 
        let go = infiniteVars (var:seen) in
        if var `elem` seen
        then return [var]
        else do
          desc <- UF.descriptor var
          case TT.structure desc of
            Nothing -> return []
            Just struct ->
                case struct of
                  TT.App1 a b -> (++) <$> go a <*> go b
                  TT.Fun1 a b -> (++) <$> go a <*> go b
                  TT.Var1 a   -> go a
                  TT.EmptyRecord1 -> return []
                  TT.Record1 fields ext -> concat <$> mapM go (ext : concat (Map.elems fields))