{-# LANGUAGE GeneralizedNewtypeDeriving #-}

module Utils.DateTime
  ( timeLocaleMap
  , TimeLocale(..)
  , currentYear
  , DateTimeFormat(..)
  , SelDateTimeFormat(..)
  , nominalHour, nominalMinute
  , minNominalYear, avgNominalYear
  , module Data.Time.Zones
  , module Data.Time.Zones.TH
  ) where

import ClassyPrelude.Yesod hiding (lift)
import System.Locale.Read

import Data.Time (NominalDiffTime, nominalDay)
import Data.Time.Zones (TZ)
import Data.Time.Zones.TH (includeSystemTZ)

import qualified Data.List.NonEmpty as NonEmpty

import Language.Haskell.TH
import Language.Haskell.TH.Syntax (Lift(..))
import Instances.TH.Lift ()

import Data.Data (Data)
import Data.Universe

import Database.Persist.Sql (PersistFieldSql)

import Utils.PathPiece

import Data.Time.Format.Instances ()

import Algebra.Lattice
import Algebra.Lattice.Ordered

import Control.Monad.Fail
  

-- $(timeLocaleMap _) :: [Lang] -> TimeLocale
timeLocaleMap :: [(Lang, String)] -- ^ Languages and matching locales, first is taken as default
              -> ExpQ
timeLocaleMap [] = fail "Need at least one (language, locale)-pair"
timeLocaleMap extra@((_, defLocale):_) = do
  localeMap <- newName "localeMap"

  let
    langs = NonEmpty.fromList $ map fst extra
    
    localeMap' = funD localeMap $ map matchLang extra ++ [defaultLang]

    defaultLang :: ClauseQ
    defaultLang =
      clause [listP []] (normalB $ localeExp defLocale) []

    matchLang :: (Lang, String) -> ClauseQ
    matchLang (lang, localeStr) = do
      lang' <- newName "lang"
      clause [varP lang'] (guardedB [(,) <$> normalG [e|selectLanguage' langs $(varE lang') == lang|] <*> localeExp localeStr]) []

    localeExp :: String -> ExpQ
    localeExp = lift <=< runIO . getLocale . Just
  
  letE [localeMap'] (varE localeMap)

currentYear :: ExpQ
currentYear = do
  now <- runIO getCurrentTime
  let (year, _, _) = toGregorian $ utctDay now
  [e|year|]


newtype DateTimeFormat = DateTimeFormat { unDateTimeFormat :: String }
  deriving (Eq, Ord, Read, Show, Data, Generic, Typeable)
  deriving newtype (ToJSON, FromJSON, PersistField, PersistFieldSql, IsString)

instance Hashable DateTimeFormat

data SelDateTimeFormat = SelFormatDate | SelFormatTime | SelFormatDateTime
  deriving (Eq, Ord, Read, Show, Enum, Bounded, Data, Generic, Typeable)

instance Universe SelDateTimeFormat
instance Finite SelDateTimeFormat
instance Hashable SelDateTimeFormat

nullaryPathPiece ''SelDateTimeFormat $ camelToPathPiece' 2
pathPieceJSON ''SelDateTimeFormat
pathPieceJSONKey ''SelDateTimeFormat

instance {-# OVERLAPPING #-} Default (SelDateTimeFormat -> DateTimeFormat) where
  def SelFormatDateTime = "%c"
  def SelFormatDate     = "%F"
  def SelFormatTime     = "%T"

instance Lattice SelDateTimeFormat where
  a \/ b = getOrdered $ ((\/) `on` Ordered) a b
  a /\ b = getOrdered $ ((/\) `on` Ordered) a b

instance BoundedJoinSemiLattice SelDateTimeFormat where
  bottom = SelFormatTime
  
instance BoundedMeetSemiLattice SelDateTimeFormat where
  top = SelFormatDateTime


---------------------
-- NominalDiffTime --
---------------------

-- | One hour in `NominalDiffTime`.
nominalHour :: NominalDiffTime
nominalHour = 3600

-- | One minute in `NominalDiffTime`.
nominalMinute :: NominalDiffTime
nominalMinute = 60

minNominalYear, avgNominalYear :: NominalDiffTime
minNominalYear = 365 * nominalDay
avgNominalYear = fromRational $ 365.2425 * toRational nominalDay