Priority.hs

-- | This module provides the type for the priority of a task.
module Taskwarrior.Priority (parseMay, Priority) where

import qualified Data.Aeson                    as Aeson
import           Data.Aeson.Types               ( Parser, typeMismatch )


-- | A task can have the priorities high, medium, low or none, which is modeled via a Maybe Priority.
data Priority = High | Medium | Low
        deriving (Eq, Show, Read, Enum, Ord, Bounded)

instance Aeson.ToJSON Priority where
   toJSON = \case
      High -> "H"
      Medium -> "M"
      Low -> "L"

-- | Parses a JSON string to a Maybe Priority, fails on anything else.
parseMay :: Aeson.Value -> Parser (Maybe Priority)
parseMay val = Aeson.withText "Priority" (\case
  "H" -> pure $ Just High
  "M" -> pure $ Just Medium
  "L" -> pure $ Just Low
  "" -> pure Nothing
  _ -> typeMismatch "Priority" val) val