{-# LANGUAGE FlexibleContexts, ScopedTypeVariables, ViewPatterns, ConstraintKinds, TupleSections, RecordWildCards, TypeFamilies #-}

module Postdelay.TimeSpec
  ( pTimeSpec
  , pTimeZone
  
  , spaceConsumer, lexeme
  ) where

import Postdelay.TimeSpec.Utils
import Postdelay.TimeSpec.Units

import Text.Megaparsec

import Control.Monad.IO.Class
import Control.Applicative
import Control.Lens hiding ((#))

import Data.Bool
import Data.Semigroup hiding (option)
import Data.Monoid (Endo(..))
import Data.Foldable
import Data.VectorSpace

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


seconds' :: Timeable t => Lens' t Time
seconds' = seconds . iso (% Second) (# Second)


pTimeSpec :: StringParser s m => m (Endo LocalTime)
pTimeSpec = label "Relative time specification" $
            choice [ pOffsets False
                   ]

pOffsets :: forall s m. StringParser s m
         => Bool -- ^ Require sign on first offset?
         -> m (Endo LocalTime)
pOffsets (bool optSigned signed -> reqSgn) = fmap fold $ (:) <$> offset reqSgn <*> many (offset optSigned)
  where
    asOffset :: Time -> Endo LocalTime
    asOffset by = Endo $ flexDT.seconds' %~ (^+^ by)
    offset :: (m Time -> m Time) -> m (Endo LocalTime)
    offset sgn = asOffset <$> lexeme (sgn timeLength) <?> "Time offset"

pTimeZone :: (StringParser s m, MonadIO m) => m (Either TimeZone TZ)
pTimeZone = label "Timezone" $
            empty