-- | This module implements some of analyses of Core expressions necessary for
-- "Test.Inspection". Normally, users of this pacakge can ignore this module. 
{-# LANGUAGE CPP, FlexibleContexts #-}
module Test.Inspection.Core
  ( slice
  , pprSlice
  , pprSliceDifference
  , eqSlice
  , freeOfType
  , doesNotAllocate
  , doesNotContainTypeClasses
  ) where

import CoreSyn
import CoreUtils
import TyCoRep
import Type
import Var
import Id
import Name
import VarEnv
import Outputable
import PprCore
import Coercion
import Util
import TyCon (TyCon, isClassTyCon)

import qualified Data.Set as S
import Control.Monad.State.Strict
import Control.Monad.Trans.Maybe
import Data.Maybe

type Slice = [(Var, CoreExpr)]

-- | Selects those bindings that define the given variable
slice :: [(Var, CoreExpr)] -> Var -> Slice
slice binds v = [(v,e) | (v,e) <- binds, v `S.member` used ]
  where
    used = execState (goV v) S.empty

    local = S.fromList (map fst binds)
    goV v | v `S.member` local = do
        seen <- gets (v `S.member`)
        unless seen $ do
            modify (S.insert v)
            let Just e = lookup v binds
            go e
          | otherwise = return ()

    go (Var v)                     = goV v
    go (Lit _ )                    = pure ()
    go (App e arg) | isTyCoArg arg = go e
    go (App e arg)                 = go e >> go arg
    go (Lam b e) | isTyVar b       = go e
    go (Lam _ e)                   = go e
    go (Let bind body)             = mapM_ go (rhssOfBind bind) >> go body
    go (Case s _ _ alts)           = go s >> mapM_ goA alts
    go (Cast e _)                  = go e
    go (Tick _ e)                  = go e
    go (Type _)                    = pure ()
    go (Coercion _)                = pure ()

    goA (_, _, e) = go e

-- | Pretty-print a slice
pprSlice :: Slice -> SDoc
pprSlice slice = withLessDetail $ pprCoreBindings [ NonRec v e  | (v,e) <- slice ]

-- | Pretty-print two slices, after removing variables occurring in both
pprSliceDifference :: Slice -> Slice -> SDoc
pprSliceDifference slice1 slice2 =
    nest 4 (hang (text "LHS" Outputable.<> colon) 4 (pprSlice slice1')) $$
    nest 4 (hang (text "RHS" Outputable.<> colon) 4 (pprSlice slice2'))
  where
    both = S.intersection (S.fromList (map fst slice1)) (S.fromList (map fst slice2))
    slice1' = filter (\(v,_) -> v `S.notMember` both) slice1
    slice2' = filter (\(v,_) -> v `S.notMember` both) slice2

withLessDetail :: SDoc -> SDoc
#if MIN_VERSION_GLASGOW_HASKELL(8,2,0,0)
withLessDetail sdoc = sdocWithDynFlags $ \dflags ->
     withPprStyle (defaultUserStyle dflags) sdoc
#else
withLessDetail sdoc = withPprStyle defaultUserStyle sdoc
#endif

type VarPair = (Var, Var)
type VarPairSet = S.Set VarPair

-- | This is a heuristic, which only works if both slices
-- have auxillary variables in the right order.
-- (This is mostly to work-around the buggy CSE in GHC-8.0)
-- It also breaks if there is shadowing.
eqSlice :: Bool {- ^ ignore types -} -> Slice -> Slice -> Bool
eqSlice _ slice1 slice2 | null slice1 || null slice2 = null slice1 == null slice2
  -- Mostly defensive programming (slices should not be empty)
eqSlice it slice1 slice2
  = step (S.singleton (fst (last slice1), fst (last slice2))) S.empty
  where
    step :: VarPairSet -> VarPairSet -> Bool
    step wanted done
        | wanted `S.isSubsetOf` done
        = True -- done
        | (x,y) : _ <- S.toList (wanted `S.difference` done)
        , (Just _, wanted') <- runState (runMaybeT (equate x y)) wanted
        = step wanted' (S.insert (x,y) done)
        | otherwise
        = False


    equate :: Var -> Var -> MaybeT (State VarPairSet) ()
    equate x y
        | it
        , Just e1 <- lookup x slice1
        , Just x' <- essentiallyVar e1
        = equated x' y
        | it
        , Just e2 <- lookup y slice2
        , Just y' <- essentiallyVar e2
        = equated x y'
        | Just e1 <- lookup x slice1
        , Just e2 <- lookup y slice2
        = go (mkRnEnv2 emptyInScopeSet) e1 e2
    equate _ _ = mzero

    equated :: Var -> Var -> MaybeT (State VarPairSet) ()
    equated x y | x == y = return ()
    equated x y = lift $ modify (S.insert (x,y))

    essentiallyVar :: CoreExpr -> Maybe Var
    essentiallyVar (App e a) | isTyCoArg a = essentiallyVar e
    essentiallyVar (Lam v e) | isTyCoVar v = essentiallyVar e
    essentiallyVar (Cast e _)              = essentiallyVar e
    essentiallyVar (Var v)                 = Just v
    essentiallyVar _                       = Nothing

    go :: RnEnv2 -> CoreExpr -> CoreExpr -> MaybeT (State (S.Set (Var,Var))) ()
    go env (Var v1) (Var v2) | rnOccL env v1 == rnOccR env v2 = pure ()
                             | otherwise = equated v1 v2
    go _   (Lit lit1)    (Lit lit2)        = guard $ lit1 == lit2
    go env (Type t1)     (Type t2)         = guard $ eqTypeX env t1 t2
    go env (Coercion co1) (Coercion co2)   = guard $ eqCoercionX env co1 co2

    go env (Cast e1 _) e2 | it             = go env e1 e2
    go env e1 (Cast e2 _) | it             = go env e1 e2
    go env (Cast e1 co1) (Cast e2 co2)     = do guard (eqCoercionX env co1 co2)
                                                go env e1 e2

    go env (App e1 a) e2 | it, isTyCoArg a = go env e1 e2
    go env e1 (App e2 a) | it, isTyCoArg a = go env e1 e2
    go env (App f1 a1)   (App f2 a2)       = go env f1 f2 >> go env a1 a2
    go env (Tick n1 e1)  (Tick n2 e2)      = guard (go_tick env n1 n2) >> go env e1 e2

    go env (Lam b e1) e2 | it, isTyCoVar b = go env e1 e2
    go env e1 (Lam b e2) | it, isTyCoVar b = go env e1 e2
    go env (Lam b1 e1)  (Lam b2 e2)
      = do guard (it || eqTypeX env (varType b1) (varType b2))
                -- False for Id/TyVar combination
           go (rnBndr2 env b1 b2) e1 e2

    go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
      = do go env r1 r2  -- No need to check binder types, since RHSs match
           go (rnBndr2 env v1 v2) e1 e2

    go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
      = do guard $ equalLength ps1 ps2
           sequence_ $ zipWith (go env') rs1 rs2
           go env' e1 e2
      where
        (bs1,rs1) = unzip ps1
        (bs2,rs2) = unzip ps2
        env' = rnBndrs2 env bs1 bs2

    go env (Case e1 b1 t1 a1) (Case e2 b2 t2 a2)
      | null a1   -- See Note [Empty case alternatives] in TrieMap
      = do guard (null a2)
           go env e1 e2
           guard (it || eqTypeX env t1 t2)
      | otherwise
      = do guard $ equalLength a1 a2
           go env e1 e2
           sequence_ $ zipWith (go_alt (rnBndr2 env b1 b2)) a1 a2

    go _ _ _ = guard False

    -----------
    go_alt env (c1, bs1, e1) (c2, bs2, e2)
      = guard (c1 == c2) >> go (rnBndrs2 env bs1 bs2) e1 e2

    go_tick :: RnEnv2 -> Tickish Id -> Tickish Id -> Bool
    go_tick env (Breakpoint lid lids) (Breakpoint rid rids)
          = lid == rid  &&  map (rnOccL env) lids == map (rnOccR env) rids
    go_tick _ l r = l == r



-- | Returns @True@ if the given core expression mentions no type constructor
-- anywhere that has the given name.
freeOfType :: Slice -> Name -> Maybe (Var, CoreExpr)
freeOfType slice tcN = allTyCons (\tc -> getName tc /= tcN) slice

allTyCons :: (TyCon -> Bool) -> Slice -> Maybe (Var, CoreExpr)
allTyCons predicate slice = listToMaybe [ (v,e) | (v,e) <- slice, not (go e) ]
  where
    goV v = goT (varType v)

    go (Var v)           = goV v
    go (Lit _ )          = True
    go (App e a)         = go e && go a
    go (Lam b e)         = goV b && go e
    go (Let bind body)   = all goB (flattenBinds [bind]) && go body
    go (Case s b _ alts) = go s && goV b && all goA alts
    go (Cast e _)        = go e
    go (Tick _ e)        = go e
    go (Type t)          = (goT t)
    go (Coercion _)      = True

    goB (b, e) = goV b && go e

    goA (_,pats, e) = all goV pats && go e

    goT (TyVarTy _)      = True
    goT (AppTy t1 t2)    = goT t1 && goT t2
    goT (TyConApp tc ts) = predicate tc && all goT ts
                        -- ↑ This is the crucial bit
    goT (ForAllTy _ t)   = goT t
#if MIN_VERSION_GLASGOW_HASKELL(8,2,0,0)
    goT (FunTy t1 t2)    = goT t1 && goT t2
#endif
    goT (LitTy _)        = True
    goT (CastTy t _)     = goT t
    goT (CoercionTy _)   = True

-- | True if the given variable binding does not allocate, if called fully
-- satisfied.
--
-- It currently does not look through function calls, which of course could
-- allocate. It should probably at least look through local function calls.
--
-- The variable is important to know the arity of the function.
doesNotAllocate :: Slice -> Maybe (Var, CoreExpr)
doesNotAllocate slice = listToMaybe [ (v,e) | (v,e) <- slice, not (go (idArity v) e) ]
  where
    go _ (Var v)
      | isDataConWorkId v, idArity v > 0 = False
    go a (Var v)                         = (a >= idArity v)
    go _ (Lit _ )                        = True
    go a (App e arg) | isTypeArg arg     = go a e
    go a (App e arg)                     = go (a+1) e && goArg arg
    go a (Lam b e) | isTyVar b           = go a e
    go 0 (Lam _ _)                       = False
    go a (Lam _ e)                       = go (a-1) e
    go a (Let bind body)                 = all goB (flattenBinds [bind]) && go a body
    go a (Case s _ _ alts)               = go 0 s && all (goA a) alts
    go a (Cast e _)                      = go a e
    go a (Tick _ e)                      = go a e
    go _ (Type _)                        = True
    go _ (Coercion _)                    = True

    goArg e | exprIsTrivial e             = go 0 e
            | isUnliftedType (exprType e) = go 0 e
            | otherwise                   = False

    goB (b, e)
#if MIN_VERSION_GLASGOW_HASKELL(8,2,0,0)
        | isJoinId b                = go (idArity b) e
#endif
        -- Not sure when a local function definition allocates…
        | isFunTy (idType b)        = go (idArity b) e
        | isUnliftedType (idType b) = go (idArity b) e
        | otherwise                 = False
        -- A let binding allocates if any variable is not a join point and not
        -- unlifted

    goA a (_,_, e) = go a e

doesNotContainTypeClasses :: Slice -> [Name] -> Maybe (Var, CoreExpr)
doesNotContainTypeClasses slice tcNs
    = allTyCons (\tc -> not (isClassTyCon tc) || any (getName tc ==) tcNs) slice