{-# OPTIONS_GHC -fno-warn-type-defaults #-}
{-# LANGUAGE OverloadedStrings, UnicodeSyntax, CPP #-}

module Scripting.Duktape (
  DuktapeCtx
, createDuktapeCtx
, evalDuktape
) where

import           Foreign.Ptr
import           Foreign.ForeignPtr
import           Foreign.Storable
import           Foreign.C.String
import           Foreign.C.Types
import           Foreign.Marshal.Alloc
import           Control.Monad.IO.Class
import           Data.Text.Encoding (decodeUtf8)
import qualified Data.ByteString as BS
import qualified Data.ByteString.Lazy as BL
import           Data.Aeson
import           Scripting.Duktape.Raw

#define DUK_TYPE_NONE                     0
#define DUK_TYPE_UNDEFINED                1
#define DUK_TYPE_NULL                     2
#define DUK_TYPE_BOOLEAN                  3
#define DUK_TYPE_NUMBER                   4
#define DUK_TYPE_STRING                   5
#define DUK_TYPE_OBJECT                   6
#define DUK_TYPE_BUFFER                   7
#define DUK_TYPE_POINTER                  8
#define DUK_TYPE_LIGHTFUNC                9

cMinusOne ∷ CInt
cMinusOne = fromIntegral $ -1

data DukType = DukNone | DukUndefined | DukNull | DukBoolean | DukNumber | DukString | DukObject | DukBuffer | DukPointer | DukLightFunc

getTypeOnStack ∷ DuktapeCtx → Int → IO DukType
getTypeOnStack ctx idx = withForeignPtr ctx $ \ctxPtr → do
  t ← c_duk_get_type ctxPtr $ fromIntegral idx
  return $ case t of
    DUK_TYPE_NONE      → DukNone
    DUK_TYPE_UNDEFINED → DukUndefined
    DUK_TYPE_NULL      → DukNull
    DUK_TYPE_BOOLEAN   → DukBoolean
    DUK_TYPE_NUMBER    → DukNumber
    DUK_TYPE_STRING    → DukString
    DUK_TYPE_OBJECT    → DukObject
    DUK_TYPE_BUFFER    → DukBuffer
    DUK_TYPE_POINTER   → DukPointer
    DUK_TYPE_LIGHTFUNC → DukLightFunc
    _                  → DukNone

getStringFromStack ∷ DuktapeCtx → Int → IO BS.ByteString
getStringFromStack ctx idx = withForeignPtr ctx $ \ctxPtr → do
  let cIdx = fromIntegral idx
  lenPtr ← malloc ∷ IO (Ptr CSize)
  str ← c_duk_get_lstring ctxPtr cIdx lenPtr
  len ← peek lenPtr
  retVal ← BS.packCStringLen (str, fromIntegral len)
  free lenPtr
  return retVal

getValueFromStack ∷ DuktapeCtx → Int → IO (Maybe Value)
getValueFromStack ctx idx = withForeignPtr ctx $ \ctxPtr → do
  retType ← getTypeOnStack ctx idx
  let cIdx = fromIntegral idx
      ret = return . Just
  case retType of
    DukNull → ret Null
    DukBoolean → c_duk_get_boolean ctxPtr cIdx >>= ret . Bool . (== 1) . fromIntegral
    DukNumber → c_duk_get_number ctxPtr cIdx >>= ret . Number . realToFrac
    DukString → getStringFromStack ctx idx >>= ret . String . decodeUtf8
    DukObject → c_duk_json_encode ctxPtr cIdx >> getStringFromStack ctx idx >>= return . decode . BL.fromStrict
    _ → return Nothing

createDuktapeCtx ∷ MonadIO μ ⇒ μ (Maybe DuktapeCtx)
createDuktapeCtx = liftIO $ createHeapF nullFunPtr

evalDuktape ∷ MonadIO μ ⇒ DuktapeCtx → BS.ByteString → μ (Either String (Maybe Value))
evalDuktape ctx src =
  liftIO $ withForeignPtr ctx $ \ctxPtr →
    BS.useAsCStringLen src $ \(srcCstr, srcLen) → do
      evalCode ← c_duk_peval_lstring ctxPtr srcCstr $ fromIntegral srcLen
      retVal ← if evalCode /= fromIntegral 0
         then c_duk_safe_to_string ctxPtr cMinusOne >>= peekCString >>= return . Left
         else getValueFromStack ctx (-1) >>= return . Right
      c_duk_pop ctxPtr
      return retVal