module Transfer.Interpreter where

import Transfer.Core.Abs
import Transfer.Core.Print

import Control.Monad
import Data.List
import Data.Maybe

import Debug.Trace

data Value = VStr String
           | VInt Integer
           | VType
           | VRec [(CIdent,Value)]
           | VAbs (Value -> Value)
           | VPi (Value -> Value)
           | VCons CIdent [Value]
  deriving (Show)

instance Show (a -> b) where
    show _ = "<<function>>"

type Env = [(CIdent,Value)]


builtin :: Env
builtin = [mkIntUn  "neg" negate,
           mkIntBin "add" (+),
           mkIntBin "sub" (-),
           mkIntBin "mul" (*),
           mkIntBin "div" div,
           mkIntBin "mod" mod,
           mkIntCmp "lt"  (<),
           mkIntCmp "le"  (<=),
           mkIntCmp "gt"  (>),
           mkIntCmp "ge"  (>=),
           mkIntCmp "eq"  (==),
           mkIntCmp "ne"  (/=)]
  where 
  mkIntUn x f = let c = CIdent ("prim_"++x++"_Int")
                 in (c, VAbs (\n -> appInt1 c (VInt . f) n))
  mkIntBin x f = let c = CIdent ("prim_"++x++"_Int")
                  in (c, VAbs (\n -> VAbs (\m -> appInt2 c (\n m -> VInt (f n m)) n m )))
  mkIntCmp x f = let c = CIdent ("prim_"++x++"_Int")
                  in (c, VAbs (\n -> VAbs (\m -> appInt2 c (\n m -> toBool (f n m)) n m)))
  toBool b = VCons (CIdent (if b then "True" else "False")) []
  appInt1 c f x = case x of
                         VInt n -> f n
                         _ -> error $ printValue x ++ " is not an integer" -- VCons c [x]
  appInt2 c f x y = case (x,y) of
                         (VInt n,VInt m) -> f n m
                         _ -> error $ printValue x ++ " and " ++ printValue y ++ " are not both integers" -- VCons c [x,y]

addModuleEnv :: Env -> Module -> Env
addModuleEnv env (Module ds) = 
    let env' = [ (c,VCons c []) | DataDecl _ _ cs <- ds, ConsDecl c _ <- cs ] 
              ++ [ (t,VCons t []) | DataDecl t _  _ <- ds ] 
              ++ [ (x,eval env' e) | ValueDecl x e <- ds]
              ++ env
     in env'

eval :: Env -> Exp -> Value
eval env x = case x of
  ELet defs exp2 -> 
      let env' = deepSeqList [ v `seq` (id, v) | LetDef id _ e <- defs, 
                                                 let v = eval env' e] 
                 ++ env
       in eval env' exp2
  ECase exp cases  -> let v = eval env exp
                          r = case firstMatch v cases of
                                  Nothing -> error $ "No pattern matched " ++ printValue v
                                  Just (e,bs) -> eval (bs++env) e
                         in v `seq` r
  EAbs id exp  -> VAbs $! (\v -> eval (bind id v ++ env) exp)
  EPi id _ exp  -> VPi $! (\v -> eval (bind id v ++ env) exp)
  EApp exp1 exp2 -> let v1 = eval env exp1
                        v2 = eval env exp2
                     in case v1 of
                               VAbs f -> f $! v2
                               VCons c vs -> (VCons $! c) $! ((++) $! vs) $! [v2]
                               _ -> error $ "Bad application (" ++ printValue v1 ++ ") (" ++ printValue v2 ++ ")"
  EProj exp id  -> let v = eval env exp
                    in case v of
                               VRec fs -> recLookup id fs
                               _ -> error $ printValue v ++ " is not a record, cannot get field " ++ printTree id

  EEmptyRec  -> VRec []
  ERecType fts -> VRec $! deepSeqList $! [ v `seq` (f,v) | FieldType  f e <- fts, let v = eval env e]
  ERec fvs     -> VRec $! deepSeqList $! [ v `seq` (f,v) | FieldValue f e <- fvs, let v = eval env e]
  EVar id  -> case lookup id env of
                    Just x -> x
                    Nothing -> error $ "Variable " ++ printTree id ++ " not in environment."
                                       ++ " Environment contains: " ++ show (map (printTree . fst) env)
  EType  -> VType
  EStr str  -> VStr str
  EInt n  -> VInt n

firstMatch :: Value -> [Case] -> Maybe (Exp,Env)
firstMatch _ [] = Nothing
firstMatch v (Case p e:cs) = case match p v of
                                            Nothing -> firstMatch v cs
                                            Just env -> {- trace (show v ++ " matched " ++ show p) $ -} Just (e,env)

bind :: PatternVariable -> Value -> Env
bind (PVVar x) v = [(x,v)]
bind PVWild _ = []

match :: Pattern -> Value -> Maybe Env
match (PCons c' ps) (VCons c vs) 
    | c == c' = if length vs == length ps 
                 then concatM $ zipWith match ps vs
                 else error $ "Wrong number of arguments to " ++ printTree c
match (PVar x) v                   = Just (bind x v)
match (PRec fps) (VRec fs) = concatM [ match p (recLookup f fs) | FieldPattern f p <- fps ]
match (PInt i) (VInt i') | i == i' = Just []
match PType VType                  = Just []
match (PStr s) (VStr s') | s == s' = Just []
match (PInt i) (VInt i') | i == i' = Just []
match _ _ = Nothing


recLookup :: CIdent -> [(CIdent,Value)] -> Value
recLookup l fs = 
    case lookup l fs of
        Just x -> x
        Nothing -> error $ printValue (VRec fs) ++ " has no field " ++ printTree l

--
-- * Utilities
--

concatM :: Monad m => [m [a]] -> m [a]
concatM = liftM concat . sequence

-- | Force a list and its values.
deepSeqList :: [a] -> [a]
deepSeqList = foldr (\x xs -> x `seq` xs `seq` (x:xs)) []

--
-- * Pretty printing of values
--

printValue :: Value -> String
printValue v = prValue 0 0 v ""
  where
  prValue p n v = case v of
              VStr s     -> shows s
              VInt i     -> shows i
              VType      -> showString "Type"
              VRec cs    -> showChar '{' . joinS (showChar ';') 
                               (map prField cs) . showChar '}'
              VAbs f     -> showString "<<function>>"
                            {- let x = "$"++show n
                             in showChar '\\' . showString (x++" -> ") 
                                    . prValue 0 (n+1) (f (VCons (CIdent x) [])) -- hacky to use VCons
                             -}
              VPi f      -> showString "<<function type>>"
              VCons c [] -> showIdent c
              VCons c vs -> parenth (showIdent c . concatS (map (\v -> spaceS . prValue 1 n v) vs))
   where prField (i,v) = showIdent i . showChar '=' . prValue 0 n v
         parenth s = if p > 0 then showChar '(' . s . showChar ')' else s
  showIdent (CIdent i) = showString i

spaceS :: ShowS
spaceS = showChar ' '

joinS :: ShowS -> [ShowS] -> ShowS
joinS glue = concatS . intersperse glue