{-# LANGUAGE RankNTypes, ConstraintKinds, TypeFamilies, FlexibleContexts, ScopedTypeVariables, ViewPatterns #-}

module Postdelay.TimeSpec.Utils where

import Control.Applicative
import Control.Monad
import Control.Lens

import Data.Time
import Data.Time.Lens
import Data.Time.Zones

import Data.Functor
import Data.AdditiveGroup

import Text.Megaparsec
import Text.Megaparsec.Prim (MonadParsec)
import qualified Text.Megaparsec.Lexer as L


type StringParser s m = (MonadParsec Dec s m, Token s ~ Char)

  
spaceConsumer :: StringParser s m => m ()
spaceConsumer = L.space (void spaceChar) empty empty

lexeme :: StringParser s m => m a -> m a
lexeme = L.lexeme spaceConsumer

signed, optSigned :: (StringParser s m, AdditiveGroup n) => m n -> m n
signed = (<*>) (lexeme sign)
optSigned = (<*>) (option id $ lexeme sign)

sign :: (StringParser s m, AdditiveGroup n) => m (n -> n)
sign = label "sign" $ choice [ char '+' $> id
                             , char '-' $> negateV
                             ]