1 files changed, 54 insertions, 0 deletions
diff --git a/src/Order.purs b/src/Order.purs
new file mode 100644
index 0000000..33c2be9
--- /dev/null
+++ b/src/Order.purs
@@ -0,0 +1,54 @@
+module Order
+  ( Order
+  , OrderKind(..)
+  , OrderDirection(..)
+  , init
+  , select
+  ) where
+
+import Prelude (class Eq, (==))
+import Data.Generic (class Generic, gEq)
+
+type Order =
+  { kind :: OrderKind
+  , direction :: OrderDirection
+  }
+
+data OrderKind =
+  Name
+  | GlycemicIndex
+  | Carbohydrates
+  | GlycemicLoad
+
+derive instance genericOrderKind :: Generic OrderKind
+
+instance eqOrderKind :: Eq OrderKind where
+  eq = gEq
+
+data OrderDirection =
+  Ascending
+  | Descending
+
+derive instance genericOrderDirection :: Generic OrderDirection
+
+instance eqOrderDirection :: Eq OrderDirection where
+  eq = gEq
+
+init :: Order
+init =
+  { kind: Name
+  , direction: initDirection
+  }
+
+select :: OrderKind -> Order -> Order
+select kind order =
+  if order.kind == kind
+    then order { direction = otherDirection order.direction }
+    else order { kind = kind, direction = initDirection }
+
+otherDirection :: OrderDirection -> OrderDirection
+otherDirection Ascending = Descending
+otherDirection Descending = Ascending
+
+initDirection :: OrderDirection
+initDirection = Ascending