1 files changed, 35 insertions, 0 deletions

diff --git a/Model/Types.hs b/Model/Types.hs
new file mode 100644
index 0000000..61bebfd
--- /dev/null
+++ b/Model/Types.hs
@@ -0,0 +1,35 @@
+{-# LANGUAGE DeriveGeneric #-}
+
+module Model.Types
+  ( ItemDate(..)
+  , isNever, isUnknown, isKnown
+  ) where
+
+import ClassyPrelude.Yesod
+
+data ItemDate = DateUnknown | DateKnown Day | DateNever
+  deriving (Eq, Ord, Show, Read, Generic)
+
+isNever, isUnknown, isKnown :: ItemDate -> Bool
+isNever DateNever = True
+isNever _ = False
+isUnknown DateUnknown = True
+isUnknown _ = False
+isKnown (DateKnown _) = True
+isKnown _ = False
+
+unknownVerb :: IsString a => a
+unknownVerb = "unknown"
+
+instance ToJSON ItemDate where
+  toJSON DateNever = Null
+  toJSON DateUnknown = String unknownVerb
+  toJSON (DateKnown d) = toJSON d
+instance FromJSON ItemDate where
+  parseJSON Null = pure DateNever
+  parseJSON v@(String inp)
+    | unknownVerb == inp = pure DateUnknown
+    | otherwise = DateKnown <$> parseJSON v
+  parseJSON v = DateKnown <$> parseJSON v
+
+derivePersistFieldJSON "ItemDate"