Base64 encoded UUIDs safe for URLs (YouTube style)

Base64UUID.hs

import Data.Char (chr, ord)
import Data.Text (Text)
import qualified Data.Text as Text
import qualified Data.Text.Encoding as Text
import qualified Data.ByteString.Lazy as BL
import qualified Data.ByteString.Base64 as Base64
import qualified Data.UUID as UUID

-- | Base64 encoded UUID (YouTube style for safe usage in URLs).
newtype Base64UUID = Base64UUID UUID deriving (Show, Eq)

toText :: Base64UUID -> Text
toText = escape (Text.dropEnd 2 (Text.decodeUtf8 (Base64.encode (BL.toStrict (UUID.toByteString uuid)))))
  where
    escape = Text.replace "+" "-" . Text.replace "/" "_"

fromText :: Text -> Maybe Base64UUID
fromText t = do
  let bs64 = Text.encodeUtf8 (unescape t <> "==")
  case Base64.decode bs64 of
    Left _ -> Nothing
    Right bs -> Base64UUID <$> UUID.fromByteString (BL.fromStrict bs)
  where
    unescape = Text.replace "-" "+" . Text.replace "_" "/"