Location.hs

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}

-- | (At least) two different XML types have a notion of locations:
--   "TSN.XML.News" and "TSN.XML.Scores". And in fact those two types
--   agree on the city, state, and country -- at least for the
--   database representation.
--
--   This module contains a data type for the common database
--   representation.
--
module TSN.Location (
  Location(..),
  pickle_location,
  -- * WARNING: these are private but exported to silence warnings
  LocationConstructor(..) )
where

-- System imports
import Data.Tuple.Curry ( uncurryN )
import Database.Groundhog () -- Required for some String instance
import Database.Groundhog.TH (
  defaultCodegenConfig,
  groundhog,
  mkPersist )
import Text.XML.HXT.Core (
  PU,
  xpElem,
  xpOption,
  xpText,
  xpTriple,
  xpWrap )


-- | Database representation of a location.
--
--   The country has always been present in the XML that we've
--   seen. The city/state however have been observed missing in some
--   cases. The Scores are better about always having a city/state,
--   but in the interest of consolidation, we've made them optional so
--   that they can be mushed together into this one type.
--
data Location =
  Location {
    city :: Maybe String,
    state :: Maybe String,
    country :: String }
  deriving (Eq, Show)


-- Generate the Groundhog code for 'Location'.
mkPersist defaultCodegenConfig [groundhog|
- entity: Location
  dbName: locations
  constructors:
    - name: Location
      uniques:
        - name: unique_location
          type: constraint
          fields: [city, state, country]
|]



-- | We also provide an (un)pickler for one common XML representation,
--   used at least in "TSN.XML.News" and "TSN.XML.Location".
--
pickle_location :: PU Location
pickle_location =
  xpElem "location" $
    xpWrap (from_tuple, to_tuple) $
    xpTriple (xpOption (xpElem "city" xpText))
             (xpOption (xpElem "state" xpText))
             (xpElem "country" xpText)
  where
    from_tuple = uncurryN Location
    to_tuple l = (city l, state l, country l)