add interested api endpoint

src/Interested.hs

@@ -0,0 +1,19 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Interested (register) where
+
+import Data.Text qualified as T
+import Data.UUID qualified as UUID
+import Data.UUID.V4 qualified as UUID.V4
+
+register :: T.Text -> Maybe T.Text -> IO T.Text
+register event identifier = do
+  cookie_uuid <- case ( case identifier of
+                          Just i -> UUID.fromString (T.unpack i)
+                          Nothing -> Nothing
+                      ) of
+    Just i -> pure i
+    Nothing -> UUID.V4.nextRandom
+  appendFile "test.txt" (T.unpack (T.filter (\c -> c /= '\n' && c /= ',') event) <> "," <> (UUID.toString cookie_uuid) <> "\n")
+
+  pure $ (UUID.toText cookie_uuid)