module Issue.TypedValue
  ( Type (..),
    cast,
    castDef,
  )
where

import Data.Maybe (fromMaybe)
import Data.Text (Text)
import Data.Text qualified as T
import Data.Time.Calendar (Day)
import Text.Read (readMaybe)

data Type a where
  Date :: Type Day
  Int :: Type Int
  String :: Type Text

cast :: (forall a. Ord a => a -> a -> b) -> (Text -> Text -> Maybe b)
cast eq x y
  | Just x' <- castTo Date x, Just y' <- castTo Date y = Just (eq x' y')
  | Just _ <- castTo Date x, Nothing <- castTo Date y = Nothing
  | Just x' <- castTo Int x, Just y' <- castTo Int y = Just (eq x' y')
  | Just _ <- castTo Int x, Nothing <- castTo Int y = Nothing
  | otherwise = Just (eq x y)

castDef :: b -> (forall a. Ord a => a -> a -> b) -> (Text -> Text -> b)
castDef def eq x y = fromMaybe def (cast eq x y)

castTo :: Type a -> Text -> Maybe a
castTo Date = readMaybe . T.unpack
castTo Int = readMaybe . T.unpack
castTo String = Just