Support for multiproject builds with nix

- Closes #28

backend/src/Servant/XML.hs

@@ -0,0 +1,44 @@
+{-# Language OverloadedStrings #-}
+{-# Language FlexibleInstances #-}
+{-# Language MultiParamTypeClasses #-}
+{-# Language TypeApplications #-}
+module Servant.XML
+  ( ToNode(..)
+  , XML
+  , OPDS
+  , Text.Hamlet.XML.xml
+  , iso8601 )
+  where
+
+import Text.XML
+import ClassyPrelude
+import Text.Hamlet.XML
+import Servant
+import Network.HTTP.Media.MediaType
+
+data XML
+
+data OPDS
+
+instance (ToNode a) => MimeRender XML a where
+  mimeRender _ a =
+    let [NodeElement root] = toNode a
+    in renderLBS def (Document (Prologue [] Nothing []) root [])
+
+instance (ToNode a) => MimeRender OPDS a where
+  mimeRender _ a = mimeRender (Proxy @XML) a
+
+instance Accept XML where
+  contentType _ = "application" // "xml" /: ("charset", "utf-8")
+
+instance Accept OPDS where
+  contentType _ = "application" // "atom+xml" /: ("charset", "utf-8") /: ("profile", "opds-catalog")
+
+iso8601 :: UTCTime -> Text
+iso8601 = pack . formatTime defaultTimeLocale "%Y-%m-%dT%H:%M:%SZ"
+
+class ToNode a where
+  toNode :: a -> [Node]
+
+instance (ToNode a) => ToNode [a] where
+  toNode = concatMap toNode