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 qualified OptionalConfiguration as OC (
  13   OptionalConfiguration(..),
  14   merge_maybes )
  15
  16 -- | The main configuration data type. This will be passed to most of
  17 --   the important functions once it has been created.
  18 --
  19 data Configuration =
  20   Configuration {
  21     database :: Maybe String,
  22     detail  :: Bool,
  23     detail_query :: String,
  24     host :: Maybe String,
  25     password :: Maybe String,
  26     port :: Maybe Int,
  27     summary_query :: String,
  28     username :: Maybe String }
  29   deriving (Show)
  30
  31
  32 -- | A Configuration with all of its fields set to their default
  33 --   values.
  34 --
  35 instance Default Configuration where
  36   def = Configuration {
  37           database = def,
  38           detail = def,
  39           detail_query = def_detail_query,
  40           host = def,
  41           password = def,
  42           port = def,
  43           summary_query = def_summary_query,
  44           username = def }
  45     where
  46       def_summary_query = "SELECT domain,COUNT(username) " ++
  47                           "FROM mailbox " ++
  48                           "GROUP BY domain "++
  49                           "ORDER BY domain;"
  50
  51       def_detail_query = "SELECT domain,username " ++
  52                          "FROM mailbox " ++
  53                          "ORDER BY domain;"
  54
  55 -- | Merge a 'Configuration' with an 'OptionalConfiguration'. This is
  56 --   more or less the Monoid instance for 'OptionalConfiguration', but
  57 --   since the two types are different, we have to repeat ourselves.
  58 --
  59 merge_optional :: Configuration
  60                -> OC.OptionalConfiguration
  61                -> Configuration
  62 merge_optional cfg opt_cfg =
  63   Configuration
  64     (OC.merge_maybes (database cfg) (OC.database opt_cfg))
  65     (merge (detail cfg) (OC.detail opt_cfg))
  66     (merge (detail_query cfg) (OC.detail_query opt_cfg))
  67     (OC.merge_maybes (host cfg) (OC.host opt_cfg))
  68     (OC.merge_maybes (password cfg) (OC.password opt_cfg))
  69     (OC.merge_maybes (port cfg) (OC.port opt_cfg))
  70     (merge (summary_query cfg) (OC.summary_query opt_cfg))
  71     (OC.merge_maybes (username cfg) (OC.username opt_cfg))
  72   where
  73     -- | If the thing on the right is Just something, return that
  74     --   something, otherwise return the thing on the left.
  75     merge :: a -> Maybe a -> a
  76     merge x Nothing  = x
  77     merge _ (Just y) = y