Re-add part3

advanced/part3/src/Viewer/Cred.elm

@@ -0,0 +1,85 @@
+module Viewer.Cred exposing (Cred, addHeader, addHeaderIfAvailable, decoder, encodeToken, username)
+
+{-| The authentication credentials for the Viewer (that is, the currently logged-in user.)
+
+This includes:
+
+  - The cred's Username
+  - The cred's authentication token
+
+By design, there is no way to access the token directly as a String.
+It can be encoded for persistence, and it can be added to a header
+to a HttpBuilder for a request, but that's it.
+
+This token should never be rendered to the end user, and with this API, it
+can't be!
+
+-}
+
+import HttpBuilder exposing (RequestBuilder, withHeader)
+import Json.Decode as Decode exposing (Decoder)
+import Json.Decode.Pipeline exposing (required)
+import Json.Encode as Encode exposing (Value)
+import Username exposing (Username)
+
+
+{-| The authentication token for the currently logged-in user.
+
+The token records the username associated with this token, which you can ask it for.
+
+By design, there is no way to access the token directly as a String. You can encode it for persistence, and you can add it to a header to a HttpBuilder for a request, but that's it.
+
+-}
+
+
+
+-- TYPES
+
+
+type Cred
+    = Cred Username String
+
+
+
+-- INFO
+
+
+username : Cred -> Username
+username (Cred val _) =
+    val
+
+
+
+-- SERIALIZATION
+
+
+decoder : Decoder Cred
+decoder =
+    Decode.succeed Cred
+        |> required "username" Username.decoder
+        |> required "token" Decode.string
+
+
+
+-- TRANSFORM
+
+
+encodeToken : Cred -> Value
+encodeToken (Cred _ str) =
+    Encode.string str
+
+
+addHeader : Cred -> RequestBuilder a -> RequestBuilder a
+addHeader (Cred _ str) builder =
+    builder
+        |> withHeader "authorization" ("Token " ++ str)
+
+
+addHeaderIfAvailable : Maybe Cred -> RequestBuilder a -> RequestBuilder a
+addHeaderIfAvailable maybeCred builder =
+    case maybeCred of
+        Just cred ->
+            addHeader cred builder
+
+        Nothing ->
+            builder