All.hs.template

-- -*- haskell -*-
{- |
Module      : Data.Time.Zones.All
Copyright   : (C) 2014 Mihaly Barasz
License     : Apache-2.0, see LICENSE
Maintainer  : Mihaly Barasz <klao@nilcons.com>
Stability   : experimental
-}

module Data.Time.Zones.All (
  toTZName,
  fromTZName,
  tzByLabel,
  tzByName,
  TZLabel(..),
  -- * Access to raw data
  TZDescription,
  tzDescriptions,
  ) where

import Control.Arrow ((&&&))
import qualified Data.ByteString.Lazy.Char8 as BL
import Data.Time.Zones.Read
import Data.Time.Zones.Types
import qualified Data.Map.Lazy as M
import qualified Data.Vector as V

-- | Enumeration of time zone locations.
data TZLabel
  TZ_LABEL_DECL
  deriving (Eq,Ord,Enum,Bounded,Show,Read)

-- | Type of the elements of the compiled-in time zone info database.
--
-- @Right@ is a primary location;
-- fields: name, label, abridged content of the Time Zone info file
--
-- @Left@ is a location which is an alias for a primary location;
-- fields: name, label, label of the target
--
-- "Abridged" means that we only store the second part of the TZif
-- file for version '2' and '3' files.
type TZDescription = Either (String, TZLabel, TZLabel) (String, TZLabel, BL.ByteString)

name :: TZDescription -> String
name = either fst' fst'
  where
    fst' (a,_,_) = a

label :: TZDescription -> TZLabel
label = either snd' snd'
  where
    snd' (_,b,_) = b

-- | Convert a `TZLabel` to the usual name of the location.
--
-- >> toTZName Europe__Paris
-- >"Europe/Paris"
toTZName :: TZLabel -> String
toTZName = (v V.!) . fromEnum
  where
    v = V.fromList $ map name tzDescriptions

-- | Lookup the `TZLabel` by the name of the location.
--
-- Returns `Nothing` if the location is unknown.
--
-- >> fromTZName "Europe/Paris"
-- >Just Europe__Paris
-- >> fromTZName "Foo/Bar"
-- >Nothing
fromTZName :: String -> Maybe TZLabel
fromTZName = flip M.lookup m
  where
    m = M.fromList $ map (name &&& label) tzDescriptions

-- | Lookup a `TZ` by its label.
--
-- >utcToNewYork :: UTCTime -> LocalTime
-- >utcToNewYork = utcToLocalTimeTZ $ tzByLabel America__New_York
tzByLabel :: TZLabel -> TZ
tzByLabel = f
  where
    f = (v V.!) . fromEnum
    v = V.fromList $ map g tzDescriptions
    g (Right (_, _, desc)) = parseTZDescription desc
    g (Left (_, _, target)) = f target

-- | Lookup a `TZ` by the name of it's location.
--
-- Returns `Nothing` if the location is unknown.
tzByName :: String -> Maybe TZ
tzByName n = tzByLabel `fmap` fromTZName n

-- | The list with raw data of the compiled-in time zone info database.
--
-- The list is guaranteed to be in the order of `TZLabel` constructors
-- (it is sorted by name).
tzDescriptions :: [TZDescription]
tzDescriptions = zones
  where
    p name' label' desc = Right (name', label', BL.pack desc)
    l name' label' target = Left (name', label', target)
    zones = [
      TZ_DESCRIPTIONS
      ]