------------------------------------------------------------------
-- |
-- Module      :  IdlFQMonad
-- Copyright   :  (c) Dmitry Golubovsky, 2009
-- License     :  BSD-style
-- 
-- Maintainer  :  golubovsky@gmail.com
-- Stability   :  experimental
-- Portability :  portable
-- 
--
--
-- A RWS Monad to help convert IDL to intermediate format.
------------------------------------------------------------------

module IdlFQMonad where

import Data.List
import Data.Maybe
import Data.Either
import qualified Data.Map as M
import Control.Monad.RWS
import Text.ParserCombinators.Parsec.Pos
import Language.WebIDL

import IdlGlobal

-- A RWS monad to implement the algorithm. The reader part is program options,
-- the writer part is the flat list of IDL modules, and the state part is the current
-- stack of enclosing modules.

data FQST = FQST {
  root :: [IDLDef]               -- root namespace (stack of definitions: modules [+interface])
 ,srcpos :: [SourcePos]          -- source position of the current module 
 ,defdecl :: M.Map String IDLDef -- existing definitions
}

type FQ a = RWS ICGlobal [Either String IDLDefinition] FQST a

-- Write an error message in the log. If source position is available, it wil be shown.

errMsg :: String -> FQ ()
errMsg s = do
  pos <- gets srcpos
  let sps = if null pos then "<no position available>" else show (head pos) ++ ": "
  (tell . return . Left) (sps ++ s)


pushdef :: IDLDef -> FQ ()
pushdef md = do
  st <- get
  put st {root = md : root st}

popdef :: FQ ()
popdef = do
  st <- get
  put st {root = tail (root st)}

pushpos :: SourcePos -> FQ ()
pushpos sp = do
  st <- get
  put st {srcpos = sp : srcpos st}

poppos :: FQ ()
poppos = do
  st <- get
  put st {srcpos = tail (srcpos st)}