Print.hs

{-# OPTIONS_GHC -fno-warn-orphans #-}
{-# LANGUAGE FlexibleInstances, GADTs, OverloadedStrings, CPP #-}
module Data.JSTarget.Print () where
import Prelude hiding (LT, GT)
import Data.JSTarget.AST
import Data.JSTarget.Op
import Data.JSTarget.PP as PP
import Data.ByteString.Builder
import Control.Monad
import Data.Char
import Numeric (showHex)
import qualified Data.ByteString.Char8 as BS
import qualified Data.ByteString.UTF8 as BS

instance Pretty Var where
  pp (Foreign name) = do
    put name
    doComment <- getOpt externalAnnotation
    when doComment . put $ byteString "/* EXTERNAL */"
  pp (Internal name@(Name _ _) comment _) = do
    hsnames <- getOpt preserveNames
    if hsnames
      then put $ buildStgName name
      else do
        pp name
        doComment <- getOpt nameComments
        when doComment $ do
          when (not $ BS.null comment) $ do
            put $ byteString "/* "
            put comment
            put $ byteString " */"

instance Pretty Name where
  pp name = finalNameFor name >>= put . buildFinalName

instance Pretty LHS where
  pp (NewVar _ v)  = "var " .+. pp v
  pp (LhsExp _ ex) = pp ex

instance Pretty Lit where
  pp (LNum d)  = put d
  pp (LStr s)  = "\"" .+. put (fixQuotes $ BS.toString s) .+. "\""
    where
      fixQuotes ('\\':xs) = "\\\\" ++ fixQuotes xs
      fixQuotes ('"':xs)  = '\\':'"'  : fixQuotes xs
      fixQuotes ('\'':xs) = '\\':'\'' : fixQuotes xs
      fixQuotes ('\r':xs) = '\\':'r'  : fixQuotes xs
      fixQuotes ('\n':xs) = '\\':'n' : fixQuotes xs
      fixQuotes (x:xs)
        | ord x <= 127    = x : fixQuotes xs
        | otherwise       = toHex x ++ fixQuotes xs
      fixQuotes _         = []
  pp (LBool b) = put b
  pp (LInt n)  = put n
  pp (LNull)   = "null"

-- | Generate a Haskell \uXXXX escape sequence for a char if it's >127.
toHex :: Char -> String
toHex c =
  case ord c of
    n | n < 127   -> [c]
      | otherwise -> "\\u" ++ exactlyFour (showHex (n `rem` 65536) "")

-- | Truncate and pad a string to exactly four characters. '0' is used for padding.
exactlyFour :: String -> String
exactlyFour s =
    pad (4-len) $ drop (len-4) s
  where
    len = length s
    pad 0 cs = cs
    pad n cs = '0' : pad (n-1) cs


-- | Default separator; comma followed by space, if spaces are enabled.
sep :: PP ()
sep = "," .+. sp

instance Pretty Exp where
  pp (Var v) =
    pp v
  pp (Lit l) =
    pp l
  pp (JSLit l) =
    put l
  pp (Not ex) = do
    case neg ex of
      Just ex' -> pp ex'
      _ -> if expPrec (Not ex) > expPrec ex
             then "!(" .+. pp ex .+. ")"
             else "!" .+. pp ex
  pp bop@(BinOp _ _ _) =
    case norm bop of
      BinOp op a b -> opParens op a b
      ex           -> pp ex
  pp (Fun args body) = do
    "function(" .+. ppList sep args .+. "){" .+. newl
    indent $ pp body
    ind .+. "}"
  pp (Call _ call f args) = do
      case call of
        Normal True  -> "B(" .+. normalCall .+. ")"
        Normal False -> normalCall
        Fast True    -> "B(" .+. fastCall .+. ")"
        Fast False   -> fastCall
        Method m     ->
          pp f .+. put (BS.cons '.' m) .+. "(" .+. ppList sep args .+. ")"
    where
      normalCall = "A(" .+. pp f .+. ",[" .+. ppList sep args .+. "])"
      fastCall = ppCallFun f .+. "(" .+. ppList sep args .+. ")"
      ppCallFun fun@(Fun _ _) = "(" .+. pp fun .+. ")"
      ppCallFun fun           = pp fun
  pp e@(Index arr ix) = do
    if expPrec e > expPrec arr
       then "(" .+. pp arr .+. ")"
       else pp arr
    "[" .+. pp ix .+. "]"
  pp (Arr exs) = do
    "[" .+. ppList sep exs .+. "]"
  pp (AssignEx l r) = do
    pp l .+. sp .+. "=" .+. sp .+. pp r
  pp e@(IfEx c th el) = do
    if expPrec e > expPrec c
       then "(" .+. pp c .+. ")"
       else pp c
    sp .+. "?" .+. sp .+. pp th .+. sp .+. ":" .+. sp .+. pp el
  pp (Eval x) = do
    "E(" .+. pp x .+. ")"
  pp (Thunk True x) = do
    "new T(function(){" .+. newl .+. indent (pp x) .+. "})"
  pp (Thunk False x) = do
    "new T(function(){" .+. newl .+. indent (pp x) .+. "},1)"

instance Pretty (Var, Exp) where
  pp (v, ex) = pp v .+. sp .+. "=" .+. sp .+. pp ex

instance Pretty Bool where
  pp True  = "true"
  pp False = "false"

-- | Print a series of NewVars at once, to avoid unnecessary "var" keywords.
ppAssigns :: Stm -> PP ()
ppAssigns stm = do
    line $ "var " .+. ppList sep assigns .+. ";"
    pp next
  where
    (assigns, next) = gather [] stm
    gather as (Assign (NewVar _ v) ex nxt) = gather ((v, ex):as) nxt
    gather as nxt                          = (reverse as, nxt)

-- | Returns the final statement in a case branch.
finalStm :: Stm -> PP Stm
finalStm s =
  case s of
    Assign _ _ s'   -> finalStm s'
    Case _ _ _ next -> finalStm next
    Forever s'      -> finalStm s'
    _               -> return s

instance Pretty Stm where
  pp (Case cond def alts next) = do
    prettyCase cond def alts
    pp next
  pp (Forever stm) = do
    line "while(1){"
    indent $ pp stm
    line "}"
  pp s@(Assign lhs ex next) = do
    case lhs of
      _ | lhs == blackHole ->
        line (pp ex .+. ";") >> pp next
      NewVar _ _ ->
        ppAssigns s
      LhsExp _ _ ->
        line (pp lhs .+. sp .+. "=" .+. sp .+. pp ex .+. ";") >> pp next
  pp (Return ex) = do
    line $ "return " .+. pp ex .+. ";"
  pp (Cont) = do
    line "continue;"
  pp (Stop) = do
    return ()
  pp (Tailcall call) = do
    line $ "return new F(function(){return " .+. pp call .+. ";});"
  pp (ThunkRet ex) = do
    line $ "return " .+. pp ex .+. ";"

neg :: Exp -> Maybe Exp
neg (BinOp Eq a b)  = Just $ BinOp Neq a b
neg (BinOp Neq a b) = Just $ BinOp Eq a b
neg (BinOp GT a b)  = Just $ BinOp LTE a b
neg (BinOp LT a b)  = Just $ BinOp GTE a b
neg (BinOp GTE a b) = Just $ BinOp LT a b    
neg (BinOp LTE a b) = Just $ BinOp GT a b
neg _               = Nothing

-- | Turn eligible case statements into if statements.
prettyCase :: Exp -> Stm -> [Alt] -> PP ()
prettyCase cond def [(con, branch)] = do
  case (def, branch) of
    (_, Stop) -> do
      line $ "if(" .+. pp (neg' (test con)) .+. "){"
      indent $ pp def
      line "}"
    (Stop, _) -> do
      line $ "if(" .+. pp (test con) .+. "){"
      indent $ pp branch
      line "}"
    _ -> do
      line $ "if(" .+. pp (test con) .+."){"
      indent $ pp branch
      line "}else{"
      indent $ pp def
      line "}"
  where
    test (Lit (LBool True))  = cond
    test (Lit (LBool False)) = Not cond
    test (Lit (LNum 0))      = Not cond
    test c                   = BinOp Eq cond c
    neg' c = maybe (Not c) id (neg c)
prettyCase _ def [] = do
  pp def
prettyCase cond def alts = do
  line $ "switch(" .+. pp cond .+. "){"
  indent $ do
    mapM_ pp alts
    line $ "default:"
    indent $ pp def
  line "}"

instance Pretty Alt where
  pp (con, branch) = do
    line $ "case " .+. pp con .+. ":"
    indent $ do
      pp branch
      s <- finalStm branch
      case s of
        Return _ -> return ()
        Cont     -> return ()
        _        -> line "break;";

opParens :: BinOp -> Exp -> Exp -> PP ()
opParens Sub a (BinOp Sub (Lit (LNum 0)) b) =
  opParens Add a b
opParens Sub a (Lit (LNum n)) | n < 0 =
  opParens Add a (Lit (LNum (-n)))
opParens Sub (Lit (LNum 0)) b =
  case b of
    BinOp _ _ _ -> " -(" .+. pp b .+. ")"
    _           -> " -" .+. pp b
opParens op a b = do
  let bparens = case b of
                  Lit (LNum n) | n < 0 -> \x -> "(".+. pp x .+. ")"
                  _                          -> parensR
  parensL a .+. put (stringUtf8 $ show op) .+. bparens b
  where
    parensL x = if expPrec x < opPrec op
                  then "(" .+. pp x .+. ")"
                  else pp x
    parensR x = if expPrec x <= opPrec op
                  then "(" .+. pp x .+. ")"
                  else pp x

-- | Normalize an operator expression by shifting parentheses to the left for
--   all associative operators and eliminating comparisons with true/false.
norm :: Exp -> Exp
norm (BinOp op a (BinOp op' b c)) | op == op' && opIsAssoc op =
  norm (BinOp op (BinOp op a b) c)
norm (BinOp Eq a (Lit (LBool True)))   = norm a
norm (BinOp Eq (Lit (LBool True)) b)   = norm b
norm (BinOp Eq a (Lit (LBool False)))  = Not (norm a)
norm (BinOp Eq (Lit (LBool False)) b)  = Not (norm b)
norm (BinOp Neq a (Lit (LBool True)))  = Not (norm a)
norm (BinOp Neq (Lit (LBool True)) b)  = Not (norm b)
norm (BinOp Neq a (Lit (LBool False))) = norm a
norm (BinOp Neq (Lit (LBool False)) b) = norm b
norm e = e