Refine our Duration api

src/Data/Duration.hs

@@ -2,17 +2,33 @@ module Data.Duration
 ( Duration(..)
 , fromSeconds
 , fromMilliseconds
+, fromMicroseconds
+, fromNanoseconds
 , toMicroseconds
 ) where
 
--- A duration suitable for timeouts.
+-- A duration suitable for timeouts stored as an int of milliseconds.
 newtype Duration = Milliseconds Int
+  deriving (Eq, Ord)
 
-fromMilliseconds :: Int -> Duration
-fromMilliseconds n = Milliseconds (n * 1000)
+instance Show Duration where
+  showsPrec _ (Milliseconds n) = shows n <> showString "ms"
 
 fromSeconds :: Int -> Duration
-fromSeconds n = Milliseconds (n * 1000)
+fromSeconds n = fromMilliseconds (n * 1000)
+
+-- milli = 10E-3 seconds
+fromMilliseconds :: Int -> Duration
+fromMilliseconds n | n <= 0    = Milliseconds 0
+                   | otherwise = Milliseconds n
+
+-- micro = 10E-6 seconds
+fromMicroseconds :: Int -> Duration
+fromMicroseconds n = fromMilliseconds (n `div` 1000)
+
+-- nano = 10E-9 seconds
+fromNanoseconds :: Int -> Duration
+fromNanoseconds n = fromMicroseconds (n `div` 1000)
 
 toMicroseconds :: Duration -> Int
 toMicroseconds (Milliseconds n) = n * 1000