implemented Handlers.i

src/Helpers.hs

@@ -28,7 +28,8 @@ module Helpers (
   makeHttps,
   editHost,
   dropParam,
-  editParam
+  editParam,
+  incStrBy
   ) where
 
 import qualified Data.List as L
@@ -118,6 +119,18 @@ editParam pName f url = do
     ) $ params url
   Just url { params = params' }
 
+-- | Increment a 'String' representation of an 'Integer' by a given
+-- amount (if possible)
+incStrBy
+  :: Integer
+  -- ^ the amount to increment by
+  -> String
+  -- ^ the 'String' to increment
+  -> Maybe String
+incStrBy n str = case reads str of
+  [(m, "")] -> Just $ show $ n + m
+  _         -> Nothing
+
 subToUrl :: T.Text -> Maybe Url
 subToUrl text = case T.splitOn "://" text of
   [protT, raw] -> do

test/HelpersSpec.hs

@@ -37,6 +37,7 @@ spec = do
   editHostSpec
   dropParamSpec
   editParamSpec
+  incStrBySpec
 
 textToUrlSpec :: Spec
 textToUrlSpec = describe "textToUrl" $ mapM_
@@ -149,6 +150,20 @@ editParamSpec = describe "editParam" $ mapM_
       , ( "c", Nothing    )
       ]
 
+incStrBySpec :: Spec
+incStrBySpec = describe "incStrBy" $ mapM_
+  ( \(n, str, expected) ->
+    context (show str ++ " + " ++ show n) $
+      it ("should be " ++ show expected) $
+        incStrBy n str `shouldBe` expected
+  )
+
+  --  number, string, expected
+  [ ( 2,      "3",    Just "5" )
+  , ( 2,      "foo",  Nothing  )
+  , ( 2,      "",     Nothing  )
+  ]
+
 simpleTxt :: T.Text
 simpleTxt = "http://example.com/"