Add part6

intro/part6/src/Article/FeedSources.elm

@@ -0,0 +1,109 @@
+module Article.FeedSources exposing (FeedSources, Source(..), after, before, fromLists, select, selected)
+
+import Article
+import Article.Tag as Tag exposing (Tag)
+import Username exposing (Username)
+import Viewer.Cred as Cred exposing (Cred)
+
+
+
+-- TYPES
+
+
+type FeedSources
+    = FeedSources
+        { before : List Source
+        , selected : Source
+        , after : List Source
+        }
+
+
+type Source
+    = YourFeed Cred
+    | GlobalFeed
+    | TagFeed Tag
+    | FavoritedFeed Username
+    | AuthorFeed Username
+
+
+
+-- BUILDING
+
+
+fromLists : Source -> List Source -> FeedSources
+fromLists selectedSource afterSources =
+    FeedSources
+        { before = []
+        , selected = selectedSource
+        , after = afterSources
+        }
+
+
+
+-- SELECTING
+
+
+select : Source -> FeedSources -> FeedSources
+select selectedSource (FeedSources sources) =
+    let
+        ( newBefore, newAfter ) =
+            (sources.before ++ (sources.selected :: sources.after))
+                -- By design, tags can only be included if they're selected.
+                |> List.filter isNotTag
+                |> splitOn (\source -> source == selectedSource)
+    in
+    FeedSources
+        { before = List.reverse newBefore
+        , selected = selectedSource
+        , after = List.reverse newAfter
+        }
+
+
+splitOn : (Source -> Bool) -> List Source -> ( List Source, List Source )
+splitOn isSelected sources =
+    let
+        ( _, newBefore, newAfter ) =
+            List.foldl (splitOnHelp isSelected) ( False, [], [] ) sources
+    in
+    ( newBefore, newAfter )
+
+
+splitOnHelp : (Source -> Bool) -> Source -> ( Bool, List Source, List Source ) -> ( Bool, List Source, List Source )
+splitOnHelp isSelected source ( foundSelected, beforeSelected, afterSelected ) =
+    if isSelected source then
+        ( True, beforeSelected, afterSelected )
+
+    else if foundSelected then
+        ( foundSelected, beforeSelected, source :: afterSelected )
+
+    else
+        ( foundSelected, source :: beforeSelected, afterSelected )
+
+
+isNotTag : Source -> Bool
+isNotTag currentSource =
+    case currentSource of
+        TagFeed _ ->
+            False
+
+        _ ->
+            True
+
+
+
+-- INFO
+
+
+selected : FeedSources -> Source
+selected (FeedSources record) =
+    record.selected
+
+
+before : FeedSources -> List Source
+before (FeedSources record) =
+    record.before
+
+
+after : FeedSources -> List Source
+after (FeedSources record) =
+    record.after