Parse durations

1 files changed, 36 insertions, 0 deletions

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