module PrevActivity where

import Types
import Crypto

import Control.Concurrent.STM

-- | Remove the prevActivity from a message. Doing this before sending
-- it over the wire saves transmitting that data, without weakening
-- security at all.
removePrevActivityHash :: AnyMessage -> AnyMessage
removePrevActivityHash msg = case msg of
	User (ActivityMessage a) -> User (go a)
	Developer (ActivityMessage a) -> Developer (go a)
	_ -> msg
  where
	go a = ActivityMessage $ a { prevActivity = Nothing }

type RecentActivity = STM (SigVerifier, [Hash])

noRecentActivity :: RecentActivity
noRecentActivity = return (mempty, [])

-- | Restore the prevActivity to a message received without one.
-- This needs a RecentActivity cache, and it tries hashes from that cache
-- as the prevActivity until it finds one that makes the message's
-- signature verify.
restorePrevActivityHash :: RecentActivity -> AnyMessage -> STM AnyMessage
restorePrevActivityHash ra msg = case msg of
	User (ActivityMessage act) -> 
		User . ActivityMessage <$> (go act =<< ra)
	Developer (ActivityMessage act) ->
		Developer . ActivityMessage <$> (go act =<< ra)
	User (ControlMessage {}) -> return msg
	Developer (ControlMessage {}) -> return msg

  where
	go act (_, []) = return act
	go act (sigverifier, (h:hs)) = do
		let act' = act { prevActivity = Just h }
		if verifySigned sigverifier act'
			then return act'
			else go act (sigverifier, hs)