{-# LANGUAGE FlexibleContexts #-}
module Substitutor
       ( substitute
       ) where


import Data.Map (Map, empty, insert, findWithDefault)
import Control.Monad (liftM2)
import Control.Monad.State (MonadState, get, modify, gets)
import Control.Monad.Except (MonadError)
import Token
import Action
import Exception


substituteOne :: ( MonadState (Map String String)  m
                 , MonadError Exception m
                 ) => Token -> [String] -> m String
substituteOne (Simple s) _ = return s
substituteOne (NumArgument n) args = return (args !! (fromIntegral n))
substituteOne (VarArgument name) _ = gets $ findWithDefault "" name
substituteOne _ _ = undefined

adder :: Bool -> String -> [String] -> [String]
adder _ s [] = [s]
adder b s l@(h : t) = if b then (s ++ h) : t
                    else s : l

substitute :: ( MonadState (Map String String)  m
              , MonadError Exception m
              ) => [TokenWithConcat] -> [String] -> m [String]
substitute [] _ = return []
substitute ((TokenWithConcat token c) : t) args = liftM2 (adder c) (substituteOne token args) (substitute t args)