Add (Optional)Configuration modules.

[dead/htsn-import.git] / src / Configuration.hs

diff --git a/src/Configuration.hs b/src/Configuration.hs
new file mode 100644 (file)
index 0000000..feefe92
--- /dev/null
+++ b/src/Configuration.hs
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+-- | This module defines the 'Configuration' type, which is just a
+--   wrapper around all of the configuration options we accept on the
+--   command line.
+--
+module Configuration (
+  Configuration(..),
+  merge_optional )
+where
+
+import System.Console.CmdArgs.Default ( Default(..) )
+import System.Log ( Priority( INFO ) )
+
+import qualified OptionalConfiguration as OC (
+  OptionalConfiguration(..),
+  merge_maybes )
+
+
+-- | The main configuration data type. This will be passed to most of
+--   the important functions once it has been created.
+data Configuration =
+  Configuration {
+    connection_string :: String,
+    log_file          :: Maybe FilePath,
+    log_level         :: Priority,
+    syslog            :: Bool }
+    deriving (Show)
+
+-- | A Configuration with all of its fields set to their default
+--   values.
+instance Default Configuration where
+  def = Configuration {
+          connection_string = def,
+          log_file          = def,
+          log_level         = INFO,
+          syslog           = def }
+
+
+-- | Merge a Configuration with an OptionalConfiguration. This is more
+--   or less the Monoid instance for OptionalConfiguration, but since
+--   the two types are different, we have to repeat ourselves.
+merge_optional :: Configuration
+               -> OC.OptionalConfiguration
+               -> Configuration
+merge_optional cfg opt_cfg =
+  Configuration
+    (merge (connection_string cfg) (OC.connection_string opt_cfg))
+    (OC.merge_maybes (log_file cfg) (OC.log_file opt_cfg))
+    (merge (log_level cfg) (OC.log_level opt_cfg))
+    (merge (syslog cfg) (OC.syslog opt_cfg))
+  where
+    -- | If the thing on the right is Just something, return that
+    --   something, otherwise return the thing on the left.
+    merge :: a -> Maybe a -> a
+    merge x Nothing  = x
+    merge _ (Just y) = y
+