implemented Helpers.editHost

src/Helpers.hs

@@ -25,6 +25,7 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 module Helpers (
   textToUrl,
   urlToText,
+  editHost
   ) where
 
 import qualified Data.List as L
@@ -62,6 +63,17 @@ urlToText url = T.pack $
       Just str -> "#" ++ str
       Nothing  -> ""
 
+-- | Edit the 'host' value of a 'Url'
+editHost
+  :: (String -> Maybe String)
+  -- ^ the transformation function
+  -> Url
+  -- ^ the Url being modified
+  -> Maybe Url
+editHost f url = do
+  host' <- f $ host url
+  Just url { host = host' }
+
 subToUrl :: T.Text -> Maybe Url
 subToUrl text = case T.splitOn "://" text of
   [protT, raw] -> do

test/HelpersSpec.hs

@@ -33,6 +33,7 @@ spec :: Spec
 spec = do
   textToUrlSpec
   urlToTextSpec
+  editHostSpec
 
 textToUrlSpec :: Spec
 textToUrlSpec = describe "textToUrl" $ mapM_
@@ -64,6 +65,22 @@ urlToTextSpec = describe "urlToText" $ mapM_
   , ( anchorUrl, anchorTxt )
   ]
 
+editHostSpec ::Spec
+editHostSpec = describe "editHost" $ mapM_
+  ( \(desc, f, url, expected) -> context desc $
+    it ("should be " ++ show expected) $
+      editHost f url `shouldBe` expected
+  )
+
+  --  description, function,       url,       expected
+  [ ( "reverse",   Just . reverse, simpleUrl, reversed )
+  , ( "fail",      const Nothing,  simpleUrl, Nothing  )
+  ]
+
+  where
+    reversed = Just simpleUrl
+      { host = reverse $ host simpleUrl }
+
 simpleTxt :: T.Text
 simpleTxt = "http://example.com/"