Omni/Id.hs


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{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE NoImplicitPrelude #-}

-- Integer-based identifier.
module Omni.Id
  ( Id (..),
    mk,
    untag,
  )
where

import Alpha
import Data.Aeson (FromJSON (..), ToJSON (..))
import Data.Binary (Binary)
import Data.Data (Data)
import Servant (FromHttpApiData (..), ToHttpApiData (..))

newtype Id entity = Id Int
  deriving (Eq, Ord, Show, Generic, Typeable, Data)

mk :: proxy entity -> Int -> Id entity
mk _ = Id

untag :: Id entity -> Int
untag (Id i) = i

instance Hashable (Id entity)

instance Binary (Id entity)

instance Enum (Id entity) where
  toEnum = mk (Proxy :: Proxy entity)
  fromEnum = untag

instance NFData (Id entity) where
  rnf (Id s) = rnf s

instance FromJSON (Id entity) where
  parseJSON = fmap Id <. parseJSON

instance ToJSON (Id entity) where
  toJSON = toJSON <. untag

-- this is just provided to satisfy Monoid, no reason to actually use it
instance Semigroup (Id entity) where
  a <> b = mk (Proxy :: Proxy entity) <| untag a + untag b

instance Monoid (Id entity) where
  mempty = mk (Proxy :: Proxy entity) 0

instance FromHttpApiData (Id entity) where
  parseUrlPiece p = mk (Proxy :: Proxy entity) </ parseUrlPiece p

instance ToHttpApiData (Id entity) where
  toUrlPiece p = untag p |> tshow