{- Copyright 2017 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU AGPL version 3 or higher.
 -}

module PrevActivity where

import Types
import Crypto

import Control.Concurrent.STM

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

type RecentActivity = STM (SigVerifier, [Hash])

-- | Restore the hashes to a message received.
-- This needs a RecentActivity cache, and it tries hashes from that cache
-- to find the one that was used when the message was sent, at which 
-- point the message's signature will verify.
restoreHashes :: RecentActivity -> MissingHashes AnyMessage -> STM AnyMessage
restoreHashes ra (MissingHashes msg) = case msg of
	User (ActivityMessage act) ->
		User . ActivityMessage <$> find act
	Developer (ActivityMessage act) ->
		Developer . ActivityMessage <$> find act
	User (ControlMessage {}) -> return msg
	Developer (ControlMessage {}) -> return msg

  where
	find act = do
		(sigverifier, l) <- ra
		let l' = Nothing : map Just l
		let ll = do
			ah <- l'
			eh <- l'
			return $ act
				{ prevActivity = ah
				, prevEntered = eh
				}
		go act sigverifier ll
	go act _ [] = return act
	go act sigverifier (l:ls) = do
		if verifySigned sigverifier l
			then return l
			else go act sigverifier ls