Add noise to sleep duration

3 files changed, 17 insertions, 3 deletions

diff --git a/ad-listener.cabal b/ad-listener.cabal
index be9c388..22f7adb 100644
--- a/ad-listener.cabal
+++ b/ad-listener.cabal
@@ -24,6 +24,7 @@ Library
     , text
     , time
     , wreq
+    , random
 
   Exposed-modules:
     FetchAd
diff --git a/src/executable/haskell/Service/AdListener.hs b/src/executable/haskell/Service/AdListener.hs
index 9af92f4..5b4d634 100644
--- a/src/executable/haskell/Service/AdListener.hs
+++ b/src/executable/haskell/Service/AdListener.hs
@@ -71,9 +71,10 @@ sleepUntilReady conf = do
     Just d -> do
       sleepSeconds d
 
-    Nothing ->
-      -- TODO 04/09/2019: Add noise
-      sleepSeconds . Conf.listenInterval $ conf
+    Nothing -> do
+      duration <- TimeUtils.addNoise (Conf.listenInterval conf) (Conf.listenIntervalNoise conf)
+      putStrLn . show $ duration
+      sleepSeconds duration
   where
     sleepSeconds =
       threadDelay . (*) 1000000 . round
diff --git a/src/lib/haskell/Utils/Time.hs b/src/lib/haskell/Utils/Time.hs
index 88aeeb6..ce36293 100644
--- a/src/lib/haskell/Utils/Time.hs
+++ b/src/lib/haskell/Utils/Time.hs
@@ -1,6 +1,7 @@
 module Utils.Time
   ( getCurrentFormattedTime
   , asleepDuration
+  , addNoise
   ) where
 
 import           Data.Text           (Text)
@@ -9,6 +10,7 @@ import           Data.Time.Clock     (DiffTime)
 import qualified Data.Time.Clock     as Clock
 import qualified Data.Time.Format    as Format
 import qualified Data.Time.LocalTime as LocalTime
+import qualified System.Random       as Random
 
 getCurrentFormattedTime :: IO Text
 getCurrentFormattedTime = do
@@ -27,3 +29,13 @@ asleepDuration from to t =
     Nothing
   where
     day = (realToFrac Clock.nominalDay) :: DiffTime
+
+-- |Add noise to a duration.
+-- > t - (n / 2) <= addNoise t n <= t + (n / 2)
+addNoise :: DiffTime -> DiffTime -> IO DiffTime
+addNoise t n = do
+  r <- Random.randomIO :: IO Float
+  return $ t + (Clock.secondsToDiffTime . round $ (r * (fromIntegral . toSeconds $ n))) - n / 2
+
+  where
+    toSeconds dt = Clock.diffTimeToPicoseconds dt `div` 10^(12 :: Integer)