src/Configuration.hs

   1 -- | This module defines the 'Configuration' type, which is just a
   2 --   wrapper around all of the configuration options we accept on the
   3 --   command line.
   4 --
   5 module Configuration (
   6   Configuration(..),
   7   merge_optional )
   8 where
   9
  10 import System.Console.CmdArgs.Default ( Default(..) )
  11
  12 import MxList (MxList(..))
  13 import qualified OptionalConfiguration as OC (
  14   OptionalConfiguration(..),
  15   merge_maybes )
  16
  17 -- | The main configuration data type. This will be passed to most of
  18 --   the important functions once it has been created.
  19 --
  20 data Configuration =
  21   Configuration {
  22     database :: Maybe String,
  23     domain_query :: String,
  24     exclude_mx :: MxList,
  25     forward_query :: String,
  26     host :: Maybe String,
  27     password :: Maybe String,
  28     port :: Maybe Int,
  29     username :: Maybe String }
  30   deriving (Show)
  31
  32
  33 -- | A Configuration with all of its fields set to their default
  34 --   values.
  35 --
  36 instance Default Configuration where
  37   def = Configuration {
  38           database = def,
  39           domain_query = def_domain_query,
  40           exclude_mx = def,
  41           forward_query = def_forward_query,
  42           host = def,
  43           password = def,
  44           port = def,
  45           username = def }
  46     where
  47       def_domain_query = "SELECT domain " ++
  48                          "FROM domain " ++
  49                          "WHERE domain <> 'ALL' " ++
  50                          "ORDER BY domain;"
  51
  52       def_forward_query = "SELECT address,goto " ++
  53                           "FROM alias " ++
  54                           "ORDER BY address;"
  55
  56 -- | Merge a 'Configuration' with an 'OptionalConfiguration'. This is
  57 --   more or less the Monoid instance for 'OptionalConfiguration', but
  58 --   since the two types are different, we have to repeat ourselves.
  59 --
  60 merge_optional :: Configuration
  61                -> OC.OptionalConfiguration
  62                -> Configuration
  63 merge_optional cfg opt_cfg =
  64   Configuration
  65     (OC.merge_maybes (database cfg) (OC.database opt_cfg))
  66     (merge (domain_query cfg) (OC.domain_query opt_cfg))
  67     all_excluded_mx
  68     (merge (forward_query cfg) (OC.forward_query opt_cfg))
  69     (OC.merge_maybes (host cfg) (OC.host opt_cfg))
  70     (OC.merge_maybes (password cfg) (OC.password opt_cfg))
  71     (OC.merge_maybes (port cfg) (OC.port opt_cfg))
  72     (OC.merge_maybes (username cfg) (OC.username opt_cfg))
  73   where
  74     -- | If the thing on the right is Just something, return that
  75     --   something, otherwise return the thing on the left.
  76     merge :: a -> Maybe a -> a
  77     merge x Nothing  = x
  78     merge _ (Just y) = y
  79
  80     -- If there are any optional usernames, use only those.
  81     all_excluded_mx = if (null (get_mxs (OC.exclude_mx opt_cfg)))
  82                       then (exclude_mx cfg)
  83                       else (OC.exclude_mx opt_cfg)