{-# LANGUAGE DeriveGeneric, FlexibleInstances #-}

module Types (
	module Types,
	Val(..)
) where

import Val

import GHC.Generics (Generic)
import Data.Aeson

-- | Things that the developer sees.
data Seen = Seen
	{ seenData :: Val
	}
	deriving (Show, Generic)

instance ToJSON Seen
instance FromJSON Seen

-- | Things that the developer enters.
data Entered = Entered
	{ enteredData :: Val
	, echoData :: Val
	-- ^ Data that is expected to be Seen, but has not been received
	-- at the time this was entered.
	}
	deriving (Show, Generic)

instance ToJSON Entered
instance FromJSON Entered

-- | An activity (either Entered or Seen) with a pointer
-- to the Activity before this one.
--
-- The Signature is over both the data in the activity, and its pointer.
data Activity a = Activity
	{ activity :: a
	, prevActivity :: (Maybe HashPointer)
	, signature :: Signature
	}
	deriving (Show, Generic)

instance ToJSON (Activity Seen)
instance FromJSON (Activity Seen)
instance ToJSON (Activity Entered)
instance FromJSON (Activity Entered)

newtype Signature = Signature Val
	deriving (Show, Generic)

instance ToJSON Signature
instance FromJSON Signature

-- | A hash pointer to something that hashes to this value.
data HashPointer = HashPointer
	{ hashMethod :: HashMethod
	, hashValue :: Val
	}
	deriving (Show, Generic, Eq)

instance ToJSON HashPointer
instance FromJSON HashPointer

-- | We use SHA256. (SHA3 is included to future proof, and because it
-- improves the generated JSON.)
data HashMethod = SHA256 | SHA3
	deriving (Show, Generic, Eq)

instance ToJSON HashMethod
instance FromJSON HashMethod