{-# 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"