5 files changed, 73 insertions, 4 deletions
diff --git a/Data/ConfigManager.hs b/Data/ConfigManager.hs
index 37da8b6..a13457c 100644
--- a/Data/ConfigManager.hs
+++ b/Data/ConfigManager.hs
@@ -34,7 +34,6 @@ module Data.ConfigManager
   ) where
 
 import Prelude hiding (lookup)
-import Text.Read (readMaybe)
 
 import Data.Text (Text)
 import qualified Data.Text as T
@@ -42,6 +41,7 @@ import qualified Data.HashMap.Strict as M
 
 import qualified Data.ConfigManager.Reader as R
 import Data.ConfigManager.Types
+import Data.ConfigManager.Instances ()
 
 -- | Load a 'Config' from a given 'FilePath'.
 
@@ -50,13 +50,13 @@ readConfig = R.readConfig Required
 
 -- | Lookup for the value associated to a name.
 
-lookup :: Read a => Name -> Config -> Either Text a
+lookup :: Configured a => Name -> Config -> Either Text a
 lookup name config =
   case M.lookup name (hashMap config) of
     Nothing ->
       Left . T.concat $ ["Value not found for Key ", name]
     Just value ->
-      case readMaybe . T.unpack $ value of
+      case convert value of
         Nothing -> Left . T.concat $ ["Reading error for key ", name]
         Just result -> Right result
 
diff --git a/Data/ConfigManager/Instances.hs b/Data/ConfigManager/Instances.hs
new file mode 100644
index 0000000..0855117
--- /dev/null
+++ b/Data/ConfigManager/Instances.hs
@@ -0,0 +1,24 @@
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE IncoherentInstances #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Data.ConfigManager.Instances
+  () where
+
+import qualified Data.Text as T
+import Data.Time.Clock (DiffTime, NominalDiffTime)
+
+import Text.Read (readMaybe)
+
+import Data.ConfigManager.Types.Internal
+import Data.ConfigManager.Parser.Duration (parseDuration)
+
+instance Configured DiffTime where
+  convert value = parseDuration value
+
+instance Configured NominalDiffTime where
+  convert value = realToFrac <$> parseDuration value
+
+instance Read a => Configured a where
+  convert = readMaybe . T.unpack
diff --git a/Data/ConfigManager/Parser/Duration.hs b/Data/ConfigManager/Parser/Duration.hs
new file mode 100644
index 0000000..f169c55
--- /dev/null
+++ b/Data/ConfigManager/Parser/Duration.hs
@@ -0,0 +1,36 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Data.ConfigManager.Parser.Duration
+  ( parseDuration
+  ) where
+
+import Control.Applicative ((<|>))
+
+import Data.Text (Text)
+import qualified Data.Text as T
+import Data.Time.Clock (DiffTime)
+import qualified Data.Time.Clock as Time
+
+import Text.Read (readMaybe)
+
+parseDuration :: Text -> Maybe DiffTime
+parseDuration input =
+  case T.splitOn " " input of
+    [count, unit] -> do
+      n <- readMaybe . T.unpack $ count
+      let matchDuration singularUnit pluralUnit seconds =
+            if ((n == 0 || n == 1) && unit == singularUnit) || (n > 1 && unit == pluralUnit)
+              then Just . Time.secondsToDiffTime $ n * seconds
+              else Nothing
+      (matchDuration "second" "seconds" second)
+        <|> (matchDuration "minute" "minutes" minute)
+        <|> (matchDuration "hour" "hours" hour)
+        <|> (matchDuration "day" "days" day)
+        <|> (matchDuration "week" "weeks" week)
+    _ -> Nothing
+  where
+    second = 1
+    minute = 60 * second
+    hour = 60 * minute
+    day = 24 * hour
+    week = 7 * day
diff --git a/Data/ConfigManager/Types.hs b/Data/ConfigManager/Types.hs
index ea2691f..8939713 100644
--- a/Data/ConfigManager/Types.hs
+++ b/Data/ConfigManager/Types.hs
@@ -12,6 +12,8 @@ module Data.ConfigManager.Types
   , Name
   , Value
   , Requirement(..)
+  , Configured
+  , convert
   ) where
 
 import Data.ConfigManager.Types.Internal
diff --git a/Data/ConfigManager/Types/Internal.hs b/Data/ConfigManager/Types/Internal.hs
index c4d5d0e..4459b01 100644
--- a/Data/ConfigManager/Types/Internal.hs
+++ b/Data/ConfigManager/Types/Internal.hs
@@ -4,10 +4,11 @@ module Data.ConfigManager.Types.Internal
   , Name
   , Value
   , Requirement(..)
+  , Configured
+  , convert
   ) where
 
 import Data.Text (Text)
-
 import Data.HashMap.Strict
 
 -- | Configuration data.
@@ -37,3 +38,9 @@ data Requirement =
   Required
   | Optional
   deriving (Eq, Read, Show)
+
+-- | This class represents types that can be converted /from/ a value /to/ a
+-- destination type
+
+class Configured a where
+  convert :: Value -> Maybe a