src/TSN/FeedHosts.hs

   1 {-# LANGUAGE DeriveDataTypeable #-}
   2
   3 -- | A newtype around a list of Strings which represent the feed
   4 --   hosts. This is all to avoid an orphan instance of Configured for
   5 --   [String] if we had defined one in e.g. OptionalConfiguration.
   6 --
   7 --   This was placed under the "TSN" namespace because its Default
   8 --   instance is specific to TSN, even though otherwise it's just a
   9 --   list of strings.
  10 --
  11 module TSN.FeedHosts
  12 where
  13
  14 -- DC is needed only for the DCT.Configured instance of String.
  15 import qualified Data.Configurator as DC()
  16 import qualified Data.Configurator.Types as DCT (
  17   Configured,
  18   Value( List ),
  19   convert )
  20 import Data.Data (Data)
  21 import System.Console.CmdArgs.Default (Default(..))
  22 import Data.Typeable (Typeable)
  23
  24
  25 newtype FeedHosts =
  26   FeedHosts { get_feed_hosts :: [String] }
  27     deriving (Data, Show, Typeable)
  28
  29 instance Default FeedHosts where
  30   -- | The default list of feed hosts. These were found by checking
  31   --   PTR records in the neighborhood of the IP address in use. There
  32   --   is a feed4.sportsnetwork.com, but it was not operational when
  33   --   this was written.
  34   def = FeedHosts ["feed1.sportsnetwork.com",
  35                    "feed2.sportsnetwork.com",
  36                    "feed3.sportsnetwork.com"]
  37
  38
  39 instance DCT.Configured FeedHosts where
  40   -- | This allows us to read a FeedHosts object out of a Configurator
  41   --   config file. By default Configurator wouldn't know what to do,
  42   --   so we have to tell it that we expect a list, and if that list
  43   --   has strings in it, we can apply the FeedHosts constructor to
  44   --   it.
  45   convert (DCT.List xs) =
  46     -- mapM gives us a Maybe [String] here.
  47     fmap FeedHosts (mapM convert_string xs)
  48     where
  49       convert_string :: DCT.Value -> Maybe String
  50       convert_string = DCT.convert
  51
  52   -- If we read anything other than a list of values out of the file,
  53   -- fail.
  54   convert _ = Nothing