implemented Handlers.dropParam

src/Helpers.hs

@@ -26,7 +26,8 @@ module Helpers (
   textToUrl,
   urlToText,
   makeHttps,
-  editHost
+  editHost,
+  dropParam
   ) where
 
 import qualified Data.List as L
@@ -84,6 +85,17 @@ editHost f url = do
   host' <- f $ host url
   Just url { host = host' }
 
+-- | Drop a parameter from a 'Url' (if present)
+dropParam
+  :: String
+  -- ^ the parameter to be dropped
+  -> Url
+  -- ^ the 'Url' being modified
+  -> Url
+dropParam pName url = let
+  params' = filter (\p -> fst p /= pName) $ params url
+  in url { params = params' }
+
 subToUrl :: T.Text -> Maybe Url
 subToUrl text = case T.splitOn "://" text of
   [protT, raw] -> do

test/HelpersSpec.hs

@@ -35,6 +35,7 @@ spec = do
   urlToTextSpec
   makeHttpsSpec
   editHostSpec
+  dropParamSpec
 
 textToUrlSpec :: Spec
 textToUrlSpec = describe "textToUrl" $ mapM_
@@ -99,6 +100,29 @@ editHostSpec = describe "editHost" $ mapM_
     reversed = Just simpleUrl
       { host = reverse $ host simpleUrl }
 
+dropParamSpec :: Spec
+dropParamSpec = describe "dropParam" $ mapM_
+  ( \(desc, p, expected) -> context desc $
+    it ("should be " ++ show expected) $
+      dropParam p url `shouldBe` expected
+  )
+
+  --  description,   param, expected
+  [ ( "with val",    "a",   withVal    )
+  , ( "without val", "b",   withoutVal )
+  , ( "not present", "c",   url        )
+  ]
+
+  where
+    url = simpleUrl
+      { params =
+        [ ("a", Just "1")
+        , ("b", Nothing)
+        ]
+      }
+    withVal    = simpleUrl { params = [("b", Nothing)] }
+    withoutVal = simpleUrl { params = [("a", Just "1")] }
+
 simpleTxt :: T.Text
 simpleTxt = "http://example.com/"